It is possible to trigger a use-after-free by:
* attaching an fentry probe to __sock_release() and the probe calling the
bpf_get_socket_cookie() helper
* running traceroute -I 1.1.1.1 on a freshly booted VM
A KASAN enabled kernel will log something like below (decoded):
[ 78.328507][ T299] ==================================================================
[ 78.329018][ T299] BUG: KASAN: slab-use-after-free in __sock_gen_cookie (./arch/x86/include/asm/atomic64_64.h:15 ./include/linux/atomic/atomic-arch-fallback.h:2583 ./include/linux/atomic/atomic-instrumented.h:1611 net/core/sock_diag.c:29)
[ 78.329366][ T299] Read of size 8 at addr ffff888007110dd8 by task traceroute/299
[ 78.329366][ T299]
[ 78.329366][ T299] CPU: 2 PID: 299 Comm: traceroute Tainted: G E 6.10.0-rc2+ #2
[ 78.329366][ T299] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
[ 78.329366][ T299] Call Trace:
[ 78.329366][ T299] <TASK>
[ 78.329366][ T299] dump_stack_lvl (lib/dump_stack.c:117 (discriminator 1))
[ 78.329366][ T299] print_report (mm/kasan/report.c:378 mm/kasan/report.c:488)
[ 78.329366][ T299] ? __sock_gen_cookie (./arch/x86/include/asm/atomic64_64.h:15 ./include/linux/atomic/atomic-arch-fallback.h:2583 ./include/linux/atomic/atomic-instrumented.h:1611 net/core/sock_diag.c:29)
[ 78.329366][ T299] kasan_report (mm/kasan/report.c:603)
[ 78.329366][ T299] ? __sock_gen_cookie (./arch/x86/include/asm/atomic64_64.h:15 ./include/linux/atomic/atomic-arch-fallback.h:2583 ./include/linux/atomic/atomic-instrumented.h:1611 net/core/sock_diag.c:29)
[ 78.329366][ T299] kasan_check_range (mm/kasan/generic.c:183 mm/kasan/generic.c:189)
[ 78.329366][ T299] __sock_gen_cookie (./arch/x86/include/asm/atomic64_64.h:15 ./include/linux/atomic/atomic-arch-fallback.h:2583 ./include/linux/atomic/atomic-instrumented.h:1611 net/core/sock_diag.c:29)
[ 78.329366][ T299] bpf_get_socket_ptr_cookie (./arch/x86/include/asm/preempt.h:94 ./include/linux/sock_diag.h:42 net/core/filter.c:5094 net/core/filter.c:5092)
[ 78.329366][ T299] bpf_prog_875642cf11f1d139___sock_release+0x6e/0x8e
[ 78.329366][ T299] bpf_trampoline_6442506592+0x47/0xaf
[ 78.329366][ T299] __sock_release (net/socket.c:652)
[ 78.329366][ T299] __sock_create (net/socket.c:1601)
[ 78.329366][ T299] ? srso_return_thunk (arch/x86/lib/retpoline.S:224)
[ 78.329366][ T299] __sys_socket (net/socket.c:1660 net/socket.c:1644 net/socket.c:1706)
[ 78.329366][ T299] ? __pfx___sys_socket (net/socket.c:1702)
[ 78.329366][ T299] ? srso_return_thunk (arch/x86/lib/retpoline.S:224)
[ 78.329366][ T299] ? up_read (./arch/x86/include/asm/atomic64_64.h:79 ./include/linux/atomic/atomic-arch-fallback.h:2749 ./include/linux/atomic/atomic-long.h:184 ./include/linux/atomic/atomic-instrumented.h:3317 kernel/locking/rwsem.c:1347 kernel/locking/rwsem.c:1622)
[ 78.329366][ T299] ? srso_return_thunk (arch/x86/lib/retpoline.S:224)
[ 78.329366][ T299] ? do_user_addr_fault (arch/x86/mm/fault.c:1419)
[ 78.329366][ T299] __x64_sys_socket (net/socket.c:1718)
[ 78.329366][ T299] ? srso_return_thunk (arch/x86/lib/retpoline.S:224)
[ 78.329366][ T299] do_syscall_64 (arch/x86/entry/common.c:52 arch/x86/entry/common.c:83)
[ 78.329366][ T299] entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130)
[ 78.329366][ T299] RIP: 0033:0x7f4022818ca7
[ 78.329366][ T299] Code: 73 01 c3 48 8b 0d 59 71 0c 00 f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 b8 29 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 29 71 0c 00 f7 d8 64 89 01 48
All code
========
0: 73 01 jae 0x3
2: c3 ret
3: 48 8b 0d 59 71 0c 00 mov 0xc7159(%rip),%rcx # 0xc7163
a: f7 d8 neg %eax
c: 64 89 01 mov %eax,%fs:(%rcx)
f: 48 83 c8 ff or $0xffffffffffffffff,%rax
13: c3 ret
14: 66 2e 0f 1f 84 00 00 cs nopw 0x0(%rax,%rax,1)
1b: 00 00 00
1e: 0f 1f 44 00 00 nopl 0x0(%rax,%rax,1)
23: b8 29 00 00 00 mov $0x29,%eax
28: 0f 05 syscall
2a:* 48 3d 01 f0 ff ff cmp $0xfffffffffffff001,%rax <-- trapping instruction
30: 73 01 jae 0x33
32: c3 ret
33: 48 8b 0d 29 71 0c 00 mov 0xc7129(%rip),%rcx # 0xc7163
3a: f7 d8 neg %eax
3c: 64 89 01 mov %eax,%fs:(%rcx)
3f: 48 rex.W
Code starting with the faulting instruction
===========================================
0: 48 3d 01 f0 ff ff cmp $0xfffffffffffff001,%rax
6: 73 01 jae 0x9
8: c3 ret
9: 48 8b 0d 29 71 0c 00 mov 0xc7129(%rip),%rcx # 0xc7139
10: f7 d8 neg %eax
12: 64 89 01 mov %eax,%fs:(%rcx)
15: 48 rex.W
[ 78.329366][ T299] RSP: 002b:00007ffd57e63db8 EFLAGS: 00000246 ORIG_RAX: 0000000000000029
[ 78.329366][ T299] RAX: ffffffffffffffda RBX: 0000000000000001 RCX: 00007f4022818ca7
[ 78.329366][ T299] RDX: 0000000000000001 RSI: 0000000000000002 RDI: 0000000000000002
[ 78.329366][ T299] RBP: 0000000000000002 R08: 0000000000000000 R09: 0000564be3dc8ec0
[ 78.329366][ T299] R10: 0c41e8ba3f6107df R11: 0000000000000246 R12: 0000564bbab801e0
[ 78.329366][ T299] R13: 0000000000000000 R14: 0000564bbab7db18 R15: 00007f4022934020
[ 78.329366][ T299] </TASK>
[ 78.329366][ T299]
[ 78.329366][ T299] Allocated by task 299 on cpu 2 at 78.328492s:
[ 78.329366][ T299] kasan_save_stack (mm/kasan/common.c:48)
[ 78.329366][ T299] kasan_save_track (mm/kasan/common.c:68)
[ 78.329366][ T299] __kasan_slab_alloc (mm/kasan/common.c:312 mm/kasan/common.c:338)
[ 78.329366][ T299] kmem_cache_alloc_noprof (mm/slub.c:3941 mm/slub.c:4000 mm/slub.c:4007)
[ 78.329366][ T299] sk_prot_alloc (net/core/sock.c:2075)
[ 78.329366][ T299] sk_alloc (net/core/sock.c:2134)
[ 78.329366][ T299] inet_create (net/ipv4/af_inet.c:327 net/ipv4/af_inet.c:252)
[ 78.329366][ T299] __sock_create (net/socket.c:1572)
[ 78.329366][ T299] __sys_socket (net/socket.c:1660 net/socket.c:1644 net/socket.c:1706)
[ 78.329366][ T299] __x64_sys_socket (net/socket.c:1718)
[ 78.329366][ T299] do_syscall_64 (arch/x86/entry/common.c:52 arch/x86/entry/common.c:83)
[ 78.329366][ T299] entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130)
[ 78.329366][ T299]
[ 78.329366][ T299] Freed by task 299 on cpu 2 at 78.328502s:
[ 78.329366][ T299] kasan_save_stack (mm/kasan/common.c:48)
[ 78.329366][ T299] kasan_save_track (mm/kasan/common.c:68)
[ 78.329366][ T299] kasan_save_free_info (mm/kasan/generic.c:582)
[ 78.329366][ T299] poison_slab_object (mm/kasan/common.c:242)
[ 78.329366][ T299] __kasan_slab_free (mm/kasan/common.c:256)
[ 78.329366][ T299] kmem_cache_free (mm/slub.c:4437 mm/slub.c:4511)
[ 78.329366][ T299] __sk_destruct (net/core/sock.c:2117 net/core/sock.c:2208)
[ 78.329366][ T299] inet_create (net/ipv4/af_inet.c:397 net/ipv4/af_inet.c:252)
[ 78.329366][ T299] __sock_create (net/socket.c:1572)
[ 78.329366][ T299] __sys_socket (net/socket.c:1660 net/socket.c:1644 net/socket.c:1706)
[ 78.329366][ T299] __x64_sys_socket (net/socket.c:1718)
[ 78.329366][ T299] do_syscall_64 (arch/x86/entry/common.c:52 arch/x86/entry/common.c:83)
[ 78.329366][ T299] entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130)
[ 78.329366][ T299]
[ 78.329366][ T299] The buggy address belongs to the object at ffff888007110d80
[ 78.329366][ T299] which belongs to the cache PING of size 976
[ 78.329366][ T299] The buggy address is located 88 bytes inside of
[ 78.329366][ T299] freed 976-byte region [ffff888007110d80, ffff888007111150)
[ 78.329366][ T299]
[ 78.329366][ T299] The buggy address belongs to the physical page:
[ 78.329366][ T299] page: refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x7110
[ 78.329366][ T299] head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
[ 78.329366][ T299] flags: 0x1ffff800000040(head|node=0|zone=1|lastcpupid=0x1ffff)
[ 78.329366][ T299] page_type: 0xffffefff(slab)
[ 78.329366][ T299] raw: 001ffff800000040 ffff888002f328c0 dead000000000122 0000000000000000
[ 78.329366][ T299] raw: 0000000000000000 00000000801c001c 00000001ffffefff 0000000000000000
[ 78.329366][ T299] head: 001ffff800000040 ffff888002f328c0 dead000000000122 0000000000000000
[ 78.329366][ T299] head: 0000000000000000 00000000801c001c 00000001ffffefff 0000000000000000
[ 78.329366][ T299] head: 001ffff800000003 ffffea00001c4401 ffffffffffffffff 0000000000000000
[ 78.329366][ T299] head: 0000000000000008 0000000000000000 00000000ffffffff 0000000000000000
[ 78.329366][ T299] page dumped because: kasan: bad access detected
[ 78.329366][ T299]
[ 78.329366][ T299] Memory state around the buggy address:
[ 78.329366][ T299] ffff888007110c80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
[ 78.329366][ T299] ffff888007110d00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
[ 78.329366][ T299] >ffff888007110d80: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
[ 78.329366][ T299] ^
[ 78.329366][ T299] ffff888007110e00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
[ 78.329366][ T299] ffff888007110e80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
[ 78.329366][ T299] ==================================================================
[ 78.366431][ T299] Disabling lock debugging due to kernel taint
Fix this by ensuring the error path of inet_create()/inet6_create do not leave
a dangling sk pointer after sk was released.
Fixes: 086c653f5862 ("sock: struct proto hash function may error")
Fixes: 610236587600 ("bpf: Add new cgroup attach type to enable sock modifications")
Cc: [email protected]
Signed-off-by: Ignat Korchagin <[email protected]>
---
net/ipv4/af_inet.c | 3 +++
net/ipv6/af_inet6.c | 3 +++
2 files changed, 6 insertions(+)
diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
index b24d74616637..db53701db29e 100644
--- a/net/ipv4/af_inet.c
+++ b/net/ipv4/af_inet.c
@@ -378,6 +378,7 @@ static int inet_create(struct net *net, struct socket *sock, int protocol,
err = sk->sk_prot->hash(sk);
if (err) {
sk_common_release(sk);
+ sock->sk = NULL;
goto out;
}
}
@@ -386,6 +387,7 @@ static int inet_create(struct net *net, struct socket *sock, int protocol,
err = sk->sk_prot->init(sk);
if (err) {
sk_common_release(sk);
+ sock->sk = NULL;
goto out;
}
}
@@ -394,6 +396,7 @@ static int inet_create(struct net *net, struct socket *sock, int protocol,
err = BPF_CGROUP_RUN_PROG_INET_SOCK(sk);
if (err) {
sk_common_release(sk);
+ sock->sk = NULL;
goto out;
}
}
diff --git a/net/ipv6/af_inet6.c b/net/ipv6/af_inet6.c
index 8041dc181bd4..6d5ebb2af928 100644
--- a/net/ipv6/af_inet6.c
+++ b/net/ipv6/af_inet6.c
@@ -254,6 +254,7 @@ static int inet6_create(struct net *net, struct socket *sock, int protocol,
err = sk->sk_prot->hash(sk);
if (err) {
sk_common_release(sk);
+ sock->sk = NULL;
goto out;
}
}
@@ -261,6 +262,7 @@ static int inet6_create(struct net *net, struct socket *sock, int protocol,
err = sk->sk_prot->init(sk);
if (err) {
sk_common_release(sk);
+ sock->sk = NULL;
goto out;
}
}
@@ -269,6 +271,7 @@ static int inet6_create(struct net *net, struct socket *sock, int protocol,
err = BPF_CGROUP_RUN_PROG_INET_SOCK(sk);
if (err) {
sk_common_release(sk);
+ sock->sk = NULL;
goto out;
}
}
--
2.39.2
From: Ignat Korchagin <[email protected]>
Date: Tue, 11 Jun 2024 19:47:16 +0100
> It is possible to trigger a use-after-free by:
> * attaching an fentry probe to __sock_release() and the probe calling the
> bpf_get_socket_cookie() helper
> * running traceroute -I 1.1.1.1 on a freshly booted VM
>
> A KASAN enabled kernel will log something like below (decoded):
> [ 78.328507][ T299] ==================================================================
> [ 78.329018][ T299] BUG: KASAN: slab-use-after-free in __sock_gen_cookie (./arch/x86/include/asm/atomic64_64.h:15 ./include/linux/atomic/atomic-arch-fallback.h:2583 ./include/linux/atomic/atomic-instrumented.h:1611 net/core/sock_diag.c:29)
> [ 78.329366][ T299] Read of size 8 at addr ffff888007110dd8 by task traceroute/299
> [ 78.329366][ T299]
> [ 78.329366][ T299] CPU: 2 PID: 299 Comm: traceroute Tainted: G E 6.10.0-rc2+ #2
> [ 78.329366][ T299] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
> [ 78.329366][ T299] Call Trace:
> [ 78.329366][ T299] <TASK>
> [ 78.329366][ T299] dump_stack_lvl (lib/dump_stack.c:117 (discriminator 1))
> [ 78.329366][ T299] print_report (mm/kasan/report.c:378 mm/kasan/report.c:488)
> [ 78.329366][ T299] ? __sock_gen_cookie (./arch/x86/include/asm/atomic64_64.h:15 ./include/linux/atomic/atomic-arch-fallback.h:2583 ./include/linux/atomic/atomic-instrumented.h:1611 net/core/sock_diag.c:29)
> [ 78.329366][ T299] kasan_report (mm/kasan/report.c:603)
> [ 78.329366][ T299] ? __sock_gen_cookie (./arch/x86/include/asm/atomic64_64.h:15 ./include/linux/atomic/atomic-arch-fallback.h:2583 ./include/linux/atomic/atomic-instrumented.h:1611 net/core/sock_diag.c:29)
> [ 78.329366][ T299] kasan_check_range (mm/kasan/generic.c:183 mm/kasan/generic.c:189)
> [ 78.329366][ T299] __sock_gen_cookie (./arch/x86/include/asm/atomic64_64.h:15 ./include/linux/atomic/atomic-arch-fallback.h:2583 ./include/linux/atomic/atomic-instrumented.h:1611 net/core/sock_diag.c:29)
> [ 78.329366][ T299] bpf_get_socket_ptr_cookie (./arch/x86/include/asm/preempt.h:94 ./include/linux/sock_diag.h:42 net/core/filter.c:5094 net/core/filter.c:5092)
> [ 78.329366][ T299] bpf_prog_875642cf11f1d139___sock_release+0x6e/0x8e
> [ 78.329366][ T299] bpf_trampoline_6442506592+0x47/0xaf
> [ 78.329366][ T299] __sock_release (net/socket.c:652)
> [ 78.329366][ T299] __sock_create (net/socket.c:1601)
> [ 78.329366][ T299] ? srso_return_thunk (arch/x86/lib/retpoline.S:224)
> [ 78.329366][ T299] __sys_socket (net/socket.c:1660 net/socket.c:1644 net/socket.c:1706)
> [ 78.329366][ T299] ? __pfx___sys_socket (net/socket.c:1702)
> [ 78.329366][ T299] ? srso_return_thunk (arch/x86/lib/retpoline.S:224)
> [ 78.329366][ T299] ? up_read (./arch/x86/include/asm/atomic64_64.h:79 ./include/linux/atomic/atomic-arch-fallback.h:2749 ./include/linux/atomic/atomic-long.h:184 ./include/linux/atomic/atomic-instrumented.h:3317 kernel/locking/rwsem.c:1347 kernel/locking/rwsem.c:1622)
> [ 78.329366][ T299] ? srso_return_thunk (arch/x86/lib/retpoline.S:224)
> [ 78.329366][ T299] ? do_user_addr_fault (arch/x86/mm/fault.c:1419)
> [ 78.329366][ T299] __x64_sys_socket (net/socket.c:1718)
> [ 78.329366][ T299] ? srso_return_thunk (arch/x86/lib/retpoline.S:224)
> [ 78.329366][ T299] do_syscall_64 (arch/x86/entry/common.c:52 arch/x86/entry/common.c:83)
> [ 78.329366][ T299] entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130)
> [ 78.329366][ T299] RIP: 0033:0x7f4022818ca7
> [ 78.329366][ T299] Code: 73 01 c3 48 8b 0d 59 71 0c 00 f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 b8 29 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 29 71 0c 00 f7 d8 64 89 01 48
> All code
> ========
> 0: 73 01 jae 0x3
> 2: c3 ret
> 3: 48 8b 0d 59 71 0c 00 mov 0xc7159(%rip),%rcx # 0xc7163
> a: f7 d8 neg %eax
> c: 64 89 01 mov %eax,%fs:(%rcx)
> f: 48 83 c8 ff or $0xffffffffffffffff,%rax
> 13: c3 ret
> 14: 66 2e 0f 1f 84 00 00 cs nopw 0x0(%rax,%rax,1)
> 1b: 00 00 00
> 1e: 0f 1f 44 00 00 nopl 0x0(%rax,%rax,1)
> 23: b8 29 00 00 00 mov $0x29,%eax
> 28: 0f 05 syscall
> 2a:* 48 3d 01 f0 ff ff cmp $0xfffffffffffff001,%rax <-- trapping instruction
> 30: 73 01 jae 0x33
> 32: c3 ret
> 33: 48 8b 0d 29 71 0c 00 mov 0xc7129(%rip),%rcx # 0xc7163
> 3a: f7 d8 neg %eax
> 3c: 64 89 01 mov %eax,%fs:(%rcx)
> 3f: 48 rex.W
>
> Code starting with the faulting instruction
> ===========================================
> 0: 48 3d 01 f0 ff ff cmp $0xfffffffffffff001,%rax
> 6: 73 01 jae 0x9
> 8: c3 ret
> 9: 48 8b 0d 29 71 0c 00 mov 0xc7129(%rip),%rcx # 0xc7139
> 10: f7 d8 neg %eax
> 12: 64 89 01 mov %eax,%fs:(%rcx)
> 15: 48 rex.W
> [ 78.329366][ T299] RSP: 002b:00007ffd57e63db8 EFLAGS: 00000246 ORIG_RAX: 0000000000000029
> [ 78.329366][ T299] RAX: ffffffffffffffda RBX: 0000000000000001 RCX: 00007f4022818ca7
> [ 78.329366][ T299] RDX: 0000000000000001 RSI: 0000000000000002 RDI: 0000000000000002
> [ 78.329366][ T299] RBP: 0000000000000002 R08: 0000000000000000 R09: 0000564be3dc8ec0
> [ 78.329366][ T299] R10: 0c41e8ba3f6107df R11: 0000000000000246 R12: 0000564bbab801e0
> [ 78.329366][ T299] R13: 0000000000000000 R14: 0000564bbab7db18 R15: 00007f4022934020
> [ 78.329366][ T299] </TASK>
> [ 78.329366][ T299]
> [ 78.329366][ T299] Allocated by task 299 on cpu 2 at 78.328492s:
> [ 78.329366][ T299] kasan_save_stack (mm/kasan/common.c:48)
> [ 78.329366][ T299] kasan_save_track (mm/kasan/common.c:68)
> [ 78.329366][ T299] __kasan_slab_alloc (mm/kasan/common.c:312 mm/kasan/common.c:338)
> [ 78.329366][ T299] kmem_cache_alloc_noprof (mm/slub.c:3941 mm/slub.c:4000 mm/slub.c:4007)
> [ 78.329366][ T299] sk_prot_alloc (net/core/sock.c:2075)
> [ 78.329366][ T299] sk_alloc (net/core/sock.c:2134)
> [ 78.329366][ T299] inet_create (net/ipv4/af_inet.c:327 net/ipv4/af_inet.c:252)
> [ 78.329366][ T299] __sock_create (net/socket.c:1572)
> [ 78.329366][ T299] __sys_socket (net/socket.c:1660 net/socket.c:1644 net/socket.c:1706)
> [ 78.329366][ T299] __x64_sys_socket (net/socket.c:1718)
> [ 78.329366][ T299] do_syscall_64 (arch/x86/entry/common.c:52 arch/x86/entry/common.c:83)
> [ 78.329366][ T299] entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130)
> [ 78.329366][ T299]
> [ 78.329366][ T299] Freed by task 299 on cpu 2 at 78.328502s:
> [ 78.329366][ T299] kasan_save_stack (mm/kasan/common.c:48)
> [ 78.329366][ T299] kasan_save_track (mm/kasan/common.c:68)
> [ 78.329366][ T299] kasan_save_free_info (mm/kasan/generic.c:582)
> [ 78.329366][ T299] poison_slab_object (mm/kasan/common.c:242)
> [ 78.329366][ T299] __kasan_slab_free (mm/kasan/common.c:256)
> [ 78.329366][ T299] kmem_cache_free (mm/slub.c:4437 mm/slub.c:4511)
> [ 78.329366][ T299] __sk_destruct (net/core/sock.c:2117 net/core/sock.c:2208)
> [ 78.329366][ T299] inet_create (net/ipv4/af_inet.c:397 net/ipv4/af_inet.c:252)
> [ 78.329366][ T299] __sock_create (net/socket.c:1572)
> [ 78.329366][ T299] __sys_socket (net/socket.c:1660 net/socket.c:1644 net/socket.c:1706)
> [ 78.329366][ T299] __x64_sys_socket (net/socket.c:1718)
> [ 78.329366][ T299] do_syscall_64 (arch/x86/entry/common.c:52 arch/x86/entry/common.c:83)
> [ 78.329366][ T299] entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130)
> [ 78.329366][ T299]
> [ 78.329366][ T299] The buggy address belongs to the object at ffff888007110d80
> [ 78.329366][ T299] which belongs to the cache PING of size 976
> [ 78.329366][ T299] The buggy address is located 88 bytes inside of
> [ 78.329366][ T299] freed 976-byte region [ffff888007110d80, ffff888007111150)
> [ 78.329366][ T299]
> [ 78.329366][ T299] The buggy address belongs to the physical page:
> [ 78.329366][ T299] page: refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x7110
> [ 78.329366][ T299] head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
> [ 78.329366][ T299] flags: 0x1ffff800000040(head|node=0|zone=1|lastcpupid=0x1ffff)
> [ 78.329366][ T299] page_type: 0xffffefff(slab)
> [ 78.329366][ T299] raw: 001ffff800000040 ffff888002f328c0 dead000000000122 0000000000000000
> [ 78.329366][ T299] raw: 0000000000000000 00000000801c001c 00000001ffffefff 0000000000000000
> [ 78.329366][ T299] head: 001ffff800000040 ffff888002f328c0 dead000000000122 0000000000000000
> [ 78.329366][ T299] head: 0000000000000000 00000000801c001c 00000001ffffefff 0000000000000000
> [ 78.329366][ T299] head: 001ffff800000003 ffffea00001c4401 ffffffffffffffff 0000000000000000
> [ 78.329366][ T299] head: 0000000000000008 0000000000000000 00000000ffffffff 0000000000000000
> [ 78.329366][ T299] page dumped because: kasan: bad access detected
> [ 78.329366][ T299]
> [ 78.329366][ T299] Memory state around the buggy address:
> [ 78.329366][ T299] ffff888007110c80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> [ 78.329366][ T299] ffff888007110d00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> [ 78.329366][ T299] >ffff888007110d80: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> [ 78.329366][ T299] ^
> [ 78.329366][ T299] ffff888007110e00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> [ 78.329366][ T299] ffff888007110e80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> [ 78.329366][ T299] ==================================================================
> [ 78.366431][ T299] Disabling lock debugging due to kernel taint
>
> Fix this by ensuring the error path of inet_create()/inet6_create do not leave
> a dangling sk pointer after sk was released.
>
> Fixes: 086c653f5862 ("sock: struct proto hash function may error")
I think this tag is wrong as bpf_get_socket_cookie() does not exist at
that time.
> Fixes: 610236587600 ("bpf: Add new cgroup attach type to enable sock modifications")
> Cc: [email protected]
> Signed-off-by: Ignat Korchagin <[email protected]>
> ---
> net/ipv4/af_inet.c | 3 +++
> net/ipv6/af_inet6.c | 3 +++
> 2 files changed, 6 insertions(+)
>
> diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
> index b24d74616637..db53701db29e 100644
> --- a/net/ipv4/af_inet.c
> +++ b/net/ipv4/af_inet.c
> @@ -378,6 +378,7 @@ static int inet_create(struct net *net, struct socket *sock, int protocol,
> err = sk->sk_prot->hash(sk);
> if (err) {
> sk_common_release(sk);
> + sock->sk = NULL;
> goto out;
> }
> }
You can add a new label and call sk_common_release() and set
NULL to sock->sk there, then reuse it for other two places.
Same for IPv6.
And curious if bpf_get_socket_cookie() can be called any socket
family to trigger the splat. e.g. ieee802154_create() seems to
have the same bug.
If so, how about clearing sock->sk in sk_common_release() ?
---8<---
diff --git a/net/core/sock.c b/net/core/sock.c
index 8629f9aecf91..bbc94954d9bf 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -3754,6 +3754,9 @@ void sk_common_release(struct sock *sk)
* until the last reference will be released.
*/
+ if (sk->sk_socket)
+ sk->sk_socket->sk = NULL;
+
sock_orphan(sk);
xfrm_sk_free_policy(sk);
---8<---
On Tue, Jun 11, 2024 at 5:55 PM Kuniyuki Iwashima <[email protected]> wrote:
>
> From: Ignat Korchagin <[email protected]>
> Date: Tue, 11 Jun 2024 19:47:16 +0100
> > It is possible to trigger a use-after-free by:
> > * attaching an fentry probe to __sock_release() and the probe calling the
> > bpf_get_socket_cookie() helper
> > * running traceroute -I 1.1.1.1 on a freshly booted VM
> >
> > A KASAN enabled kernel will log something like below (decoded):
> > [ 78.328507][ T299] ==================================================================
> > [ 78.329018][ T299] BUG: KASAN: slab-use-after-free in __sock_gen_cookie (./arch/x86/include/asm/atomic64_64.h:15 ./include/linux/atomic/atomic-arch-fallback.h:2583 ./include/linux/atomic/atomic-instrumented.h:1611 net/core/sock_diag.c:29)
> > [ 78.329366][ T299] Read of size 8 at addr ffff888007110dd8 by task traceroute/299
> > [ 78.329366][ T299]
> > [ 78.329366][ T299] CPU: 2 PID: 299 Comm: traceroute Tainted: G E 6.10.0-rc2+ #2
> > [ 78.329366][ T299] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
> > [ 78.329366][ T299] Call Trace:
> > [ 78.329366][ T299] <TASK>
> > [ 78.329366][ T299] dump_stack_lvl (lib/dump_stack.c:117 (discriminator 1))
> > [ 78.329366][ T299] print_report (mm/kasan/report.c:378 mm/kasan/report.c:488)
> > [ 78.329366][ T299] ? __sock_gen_cookie (./arch/x86/include/asm/atomic64_64.h:15 ./include/linux/atomic/atomic-arch-fallback.h:2583 ./include/linux/atomic/atomic-instrumented.h:1611 net/core/sock_diag.c:29)
> > [ 78.329366][ T299] kasan_report (mm/kasan/report.c:603)
> > [ 78.329366][ T299] ? __sock_gen_cookie (./arch/x86/include/asm/atomic64_64.h:15 ./include/linux/atomic/atomic-arch-fallback.h:2583 ./include/linux/atomic/atomic-instrumented.h:1611 net/core/sock_diag.c:29)
> > [ 78.329366][ T299] kasan_check_range (mm/kasan/generic.c:183 mm/kasan/generic.c:189)
> > [ 78.329366][ T299] __sock_gen_cookie (./arch/x86/include/asm/atomic64_64.h:15 ./include/linux/atomic/atomic-arch-fallback.h:2583 ./include/linux/atomic/atomic-instrumented.h:1611 net/core/sock_diag.c:29)
> > [ 78.329366][ T299] bpf_get_socket_ptr_cookie (./arch/x86/include/asm/preempt.h:94 ./include/linux/sock_diag.h:42 net/core/filter.c:5094 net/core/filter.c:5092)
> > [ 78.329366][ T299] bpf_prog_875642cf11f1d139___sock_release+0x6e/0x8e
> > [ 78.329366][ T299] bpf_trampoline_6442506592+0x47/0xaf
> > [ 78.329366][ T299] __sock_release (net/socket.c:652)
> > [ 78.329366][ T299] __sock_create (net/socket.c:1601)
> > [ 78.329366][ T299] ? srso_return_thunk (arch/x86/lib/retpoline.S:224)
> > [ 78.329366][ T299] __sys_socket (net/socket.c:1660 net/socket.c:1644 net/socket.c:1706)
> > [ 78.329366][ T299] ? __pfx___sys_socket (net/socket.c:1702)
> > [ 78.329366][ T299] ? srso_return_thunk (arch/x86/lib/retpoline.S:224)
> > [ 78.329366][ T299] ? up_read (./arch/x86/include/asm/atomic64_64.h:79 ./include/linux/atomic/atomic-arch-fallback.h:2749 ./include/linux/atomic/atomic-long.h:184 ./include/linux/atomic/atomic-instrumented.h:3317 kernel/locking/rwsem.c:1347 kernel/locking/rwsem.c:1622)
> > [ 78.329366][ T299] ? srso_return_thunk (arch/x86/lib/retpoline.S:224)
> > [ 78.329366][ T299] ? do_user_addr_fault (arch/x86/mm/fault.c:1419)
> > [ 78.329366][ T299] __x64_sys_socket (net/socket.c:1718)
> > [ 78.329366][ T299] ? srso_return_thunk (arch/x86/lib/retpoline.S:224)
> > [ 78.329366][ T299] do_syscall_64 (arch/x86/entry/common.c:52 arch/x86/entry/common.c:83)
> > [ 78.329366][ T299] entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130)
> > [ 78.329366][ T299] RIP: 0033:0x7f4022818ca7
> > [ 78.329366][ T299] Code: 73 01 c3 48 8b 0d 59 71 0c 00 f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 b8 29 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 29 71 0c 00 f7 d8 64 89 01 48
> > All code
> > ========
> > 0: 73 01 jae 0x3
> > 2: c3 ret
> > 3: 48 8b 0d 59 71 0c 00 mov 0xc7159(%rip),%rcx # 0xc7163
> > a: f7 d8 neg %eax
> > c: 64 89 01 mov %eax,%fs:(%rcx)
> > f: 48 83 c8 ff or $0xffffffffffffffff,%rax
> > 13: c3 ret
> > 14: 66 2e 0f 1f 84 00 00 cs nopw 0x0(%rax,%rax,1)
> > 1b: 00 00 00
> > 1e: 0f 1f 44 00 00 nopl 0x0(%rax,%rax,1)
> > 23: b8 29 00 00 00 mov $0x29,%eax
> > 28: 0f 05 syscall
> > 2a:* 48 3d 01 f0 ff ff cmp $0xfffffffffffff001,%rax <-- trapping instruction
> > 30: 73 01 jae 0x33
> > 32: c3 ret
> > 33: 48 8b 0d 29 71 0c 00 mov 0xc7129(%rip),%rcx # 0xc7163
> > 3a: f7 d8 neg %eax
> > 3c: 64 89 01 mov %eax,%fs:(%rcx)
> > 3f: 48 rex.W
> >
> > Code starting with the faulting instruction
> > ===========================================
> > 0: 48 3d 01 f0 ff ff cmp $0xfffffffffffff001,%rax
> > 6: 73 01 jae 0x9
> > 8: c3 ret
> > 9: 48 8b 0d 29 71 0c 00 mov 0xc7129(%rip),%rcx # 0xc7139
> > 10: f7 d8 neg %eax
> > 12: 64 89 01 mov %eax,%fs:(%rcx)
> > 15: 48 rex.W
> > [ 78.329366][ T299] RSP: 002b:00007ffd57e63db8 EFLAGS: 00000246 ORIG_RAX: 0000000000000029
> > [ 78.329366][ T299] RAX: ffffffffffffffda RBX: 0000000000000001 RCX: 00007f4022818ca7
> > [ 78.329366][ T299] RDX: 0000000000000001 RSI: 0000000000000002 RDI: 0000000000000002
> > [ 78.329366][ T299] RBP: 0000000000000002 R08: 0000000000000000 R09: 0000564be3dc8ec0
> > [ 78.329366][ T299] R10: 0c41e8ba3f6107df R11: 0000000000000246 R12: 0000564bbab801e0
> > [ 78.329366][ T299] R13: 0000000000000000 R14: 0000564bbab7db18 R15: 00007f4022934020
> > [ 78.329366][ T299] </TASK>
> > [ 78.329366][ T299]
> > [ 78.329366][ T299] Allocated by task 299 on cpu 2 at 78.328492s:
> > [ 78.329366][ T299] kasan_save_stack (mm/kasan/common.c:48)
> > [ 78.329366][ T299] kasan_save_track (mm/kasan/common.c:68)
> > [ 78.329366][ T299] __kasan_slab_alloc (mm/kasan/common.c:312 mm/kasan/common.c:338)
> > [ 78.329366][ T299] kmem_cache_alloc_noprof (mm/slub.c:3941 mm/slub.c:4000 mm/slub.c:4007)
> > [ 78.329366][ T299] sk_prot_alloc (net/core/sock.c:2075)
> > [ 78.329366][ T299] sk_alloc (net/core/sock.c:2134)
> > [ 78.329366][ T299] inet_create (net/ipv4/af_inet.c:327 net/ipv4/af_inet.c:252)
> > [ 78.329366][ T299] __sock_create (net/socket.c:1572)
> > [ 78.329366][ T299] __sys_socket (net/socket.c:1660 net/socket.c:1644 net/socket.c:1706)
> > [ 78.329366][ T299] __x64_sys_socket (net/socket.c:1718)
> > [ 78.329366][ T299] do_syscall_64 (arch/x86/entry/common.c:52 arch/x86/entry/common.c:83)
> > [ 78.329366][ T299] entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130)
> > [ 78.329366][ T299]
> > [ 78.329366][ T299] Freed by task 299 on cpu 2 at 78.328502s:
> > [ 78.329366][ T299] kasan_save_stack (mm/kasan/common.c:48)
> > [ 78.329366][ T299] kasan_save_track (mm/kasan/common.c:68)
> > [ 78.329366][ T299] kasan_save_free_info (mm/kasan/generic.c:582)
> > [ 78.329366][ T299] poison_slab_object (mm/kasan/common.c:242)
> > [ 78.329366][ T299] __kasan_slab_free (mm/kasan/common.c:256)
> > [ 78.329366][ T299] kmem_cache_free (mm/slub.c:4437 mm/slub.c:4511)
> > [ 78.329366][ T299] __sk_destruct (net/core/sock.c:2117 net/core/sock.c:2208)
> > [ 78.329366][ T299] inet_create (net/ipv4/af_inet.c:397 net/ipv4/af_inet.c:252)
> > [ 78.329366][ T299] __sock_create (net/socket.c:1572)
> > [ 78.329366][ T299] __sys_socket (net/socket.c:1660 net/socket.c:1644 net/socket.c:1706)
> > [ 78.329366][ T299] __x64_sys_socket (net/socket.c:1718)
> > [ 78.329366][ T299] do_syscall_64 (arch/x86/entry/common.c:52 arch/x86/entry/common.c:83)
> > [ 78.329366][ T299] entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130)
> > [ 78.329366][ T299]
> > [ 78.329366][ T299] The buggy address belongs to the object at ffff888007110d80
> > [ 78.329366][ T299] which belongs to the cache PING of size 976
> > [ 78.329366][ T299] The buggy address is located 88 bytes inside of
> > [ 78.329366][ T299] freed 976-byte region [ffff888007110d80, ffff888007111150)
> > [ 78.329366][ T299]
> > [ 78.329366][ T299] The buggy address belongs to the physical page:
> > [ 78.329366][ T299] page: refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x7110
> > [ 78.329366][ T299] head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
> > [ 78.329366][ T299] flags: 0x1ffff800000040(head|node=0|zone=1|lastcpupid=0x1ffff)
> > [ 78.329366][ T299] page_type: 0xffffefff(slab)
> > [ 78.329366][ T299] raw: 001ffff800000040 ffff888002f328c0 dead000000000122 0000000000000000
> > [ 78.329366][ T299] raw: 0000000000000000 00000000801c001c 00000001ffffefff 0000000000000000
> > [ 78.329366][ T299] head: 001ffff800000040 ffff888002f328c0 dead000000000122 0000000000000000
> > [ 78.329366][ T299] head: 0000000000000000 00000000801c001c 00000001ffffefff 0000000000000000
> > [ 78.329366][ T299] head: 001ffff800000003 ffffea00001c4401 ffffffffffffffff 0000000000000000
> > [ 78.329366][ T299] head: 0000000000000008 0000000000000000 00000000ffffffff 0000000000000000
> > [ 78.329366][ T299] page dumped because: kasan: bad access detected
> > [ 78.329366][ T299]
> > [ 78.329366][ T299] Memory state around the buggy address:
> > [ 78.329366][ T299] ffff888007110c80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> > [ 78.329366][ T299] ffff888007110d00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> > [ 78.329366][ T299] >ffff888007110d80: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> > [ 78.329366][ T299] ^
> > [ 78.329366][ T299] ffff888007110e00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> > [ 78.329366][ T299] ffff888007110e80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> > [ 78.329366][ T299] ==================================================================
> > [ 78.366431][ T299] Disabling lock debugging due to kernel taint
> >
> > Fix this by ensuring the error path of inet_create()/inet6_create do not leave
> > a dangling sk pointer after sk was released.
> >
> > Fixes: 086c653f5862 ("sock: struct proto hash function may error")
>
> I think this tag is wrong as bpf_get_socket_cookie() does not exist at
> that time.
OK - will probably replace the tag with the commit that added it.
>
> > Fixes: 610236587600 ("bpf: Add new cgroup attach type to enable sock modifications")
> > Cc: [email protected]
> > Signed-off-by: Ignat Korchagin <[email protected]>
> > ---
> > net/ipv4/af_inet.c | 3 +++
> > net/ipv6/af_inet6.c | 3 +++
> > 2 files changed, 6 insertions(+)
> >
> > diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
> > index b24d74616637..db53701db29e 100644
> > --- a/net/ipv4/af_inet.c
> > +++ b/net/ipv4/af_inet.c
> > @@ -378,6 +378,7 @@ static int inet_create(struct net *net, struct socket *sock, int protocol,
> > err = sk->sk_prot->hash(sk);
> > if (err) {
> > sk_common_release(sk);
> > + sock->sk = NULL;
> > goto out;
> > }
> > }
>
> You can add a new label and call sk_common_release() and set
> NULL to sock->sk there, then reuse it for other two places.
>
> Same for IPv6.
OK
> And curious if bpf_get_socket_cookie() can be called any socket
> family to trigger the splat. e.g. ieee802154_create() seems to
> have the same bug.
Just judging from the code - yes, indeed.
> If so, how about clearing sock->sk in sk_common_release() ?
This was my first thought, but I was a bit put off by the fact that
sk_common_release() is called from many places and the sk object
itself is reference counted. So not every call to sk_common_release()
seems to actually free the sk object. Secondly, I was put off by this
comment (which I don't fully understand TBH) [1]
On the other hand - in inet/inet6_create() we definitely know that the
object would be freed, because we just created that.
But if someone more familiar with the code confirms it is
better/possible to do in sk_common_release(), I'm happy to adjust and
it would be cleaner indeed.
> ---8<---
> diff --git a/net/core/sock.c b/net/core/sock.c
> index 8629f9aecf91..bbc94954d9bf 100644
> --- a/net/core/sock.c
> +++ b/net/core/sock.c
> @@ -3754,6 +3754,9 @@ void sk_common_release(struct sock *sk)
> * until the last reference will be released.
> */
>
> + if (sk->sk_socket)
> + sk->sk_socket->sk = NULL;
> +
> sock_orphan(sk);
>
> xfrm_sk_free_policy(sk);
> ---8<---
[1]: https://elixir.bootlin.com/linux/v6.10-rc3/source/include/net/sock.h#L1985
From: Ignat Korchagin <[email protected]>
Date: Wed, 12 Jun 2024 14:22:36 -0400
> > And curious if bpf_get_socket_cookie() can be called any socket
> > family to trigger the splat. e.g. ieee802154_create() seems to
> > have the same bug.
>
> Just judging from the code - yes, indeed.
>
> > If so, how about clearing sock->sk in sk_common_release() ?
>
> This was my first thought, but I was a bit put off by the fact that
> sk_common_release() is called from many places and the sk object
> itself is reference counted. So not every call to sk_common_release()
> seems to actually free the sk object.
sk_common_release() is called
1. when we fail to create a socket (socket() or accept() syscall)
2. when we release the last refcount of the socket's file descriptor
(basically close() syscall)
The issue only happens at 1. because we clear sock->sk at 2. in
__sock_release() after calling sock->ops->release().
So, we need not take care of these callers of sk_common_release().
- inet_release
- ->close()
- udp_lib_close
- ping_close
- raw_close
- rawv6_close
- l2tp_ip_close
- l2tp_ip6_close
- sctp_close
- ieee802154_sock_release
- ->close()
- raw_close
- dgram_close
- mctp_release
- ->close()
- mctp_sk_close
- pn_socket_release
- ->close()
- pn_sock_close
- pep_sock_close
Then, the rest of the callers are:
- __sock_create
- pf->create()
- inet_create
- inet6_create
- ieee802154_create
- smc_create
- __smc_create
- setsockopt(TCP_ULP)
- smc_ulp_init
- __smc_create
- sctp_accept
- sctp_v4_create_accept_sk
- sctp_v6_create_accept_sk
we need not care about sctp_v[46]_create_accept_sk() because they don't set
sock->sk for the socket; we don't pass sock to sock_init_data(NULL, newsk)
before calling sk_common_release().
__sock_create() path and SMC's ULP path have the same issue, and
sk_common_release() releases the last refcount of struct sock there.
So, I think we can set NULL to sock->sk in sk_common_release().
> Secondly, I was put off by this
> comment (which I don't fully understand TBH) [1]
>
> On the other hand - in inet/inet6_create() we definitely know that the
> object would be freed, because we just created that.
>
> But if someone more familiar with the code confirms it is
> better/possible to do in sk_common_release(), I'm happy to adjust and
> it would be cleaner indeed.
>
> > ---8<---
> > diff --git a/net/core/sock.c b/net/core/sock.c
> > index 8629f9aecf91..bbc94954d9bf 100644
> > --- a/net/core/sock.c
> > +++ b/net/core/sock.c
> > @@ -3754,6 +3754,9 @@ void sk_common_release(struct sock *sk)
> > * until the last reference will be released.
> > */
> >
> > + if (sk->sk_socket)
> > + sk->sk_socket->sk = NULL;
> > +
> > sock_orphan(sk);
> >
> > xfrm_sk_free_policy(sk);
> > ---8<---
>
> [1]: https://elixir.bootlin.com/linux/v6.10-rc3/source/include/net/sock.h#L1985
On Thu, Jun 13, 2024 at 3:41 PM Kuniyuki Iwashima <[email protected]> wrote:
>
> From: Ignat Korchagin <[email protected]>
> Date: Wed, 12 Jun 2024 14:22:36 -0400
> > > And curious if bpf_get_socket_cookie() can be called any socket
> > > family to trigger the splat. e.g. ieee802154_create() seems to
> > > have the same bug.
> >
> > Just judging from the code - yes, indeed.
> >
> > > If so, how about clearing sock->sk in sk_common_release() ?
> >
> > This was my first thought, but I was a bit put off by the fact that
> > sk_common_release() is called from many places and the sk object
> > itself is reference counted. So not every call to sk_common_release()
> > seems to actually free the sk object.
>
> sk_common_release() is called
>
> 1. when we fail to create a socket (socket() or accept() syscall)
> 2. when we release the last refcount of the socket's file descriptor
> (basically close() syscall)
>
> The issue only happens at 1. because we clear sock->sk at 2. in
> __sock_release() after calling sock->ops->release().
>
> So, we need not take care of these callers of sk_common_release().
>
> - inet_release
> - ->close()
> - udp_lib_close
> - ping_close
> - raw_close
> - rawv6_close
> - l2tp_ip_close
> - l2tp_ip6_close
> - sctp_close
> - ieee802154_sock_release
> - ->close()
> - raw_close
> - dgram_close
> - mctp_release
> - ->close()
> - mctp_sk_close
> - pn_socket_release
> - ->close()
> - pn_sock_close
> - pep_sock_close
>
> Then, the rest of the callers are:
>
> - __sock_create
> - pf->create()
> - inet_create
> - inet6_create
> - ieee802154_create
> - smc_create
> - __smc_create
>
> - setsockopt(TCP_ULP)
> - smc_ulp_init
> - __smc_create
>
> - sctp_accept
> - sctp_v4_create_accept_sk
> - sctp_v6_create_accept_sk
>
> we need not care about sctp_v[46]_create_accept_sk() because they don't set
> sock->sk for the socket; we don't pass sock to sock_init_data(NULL, newsk)
> before calling sk_common_release().
>
> __sock_create() path and SMC's ULP path have the same issue, and
> sk_common_release() releases the last refcount of struct sock there.
>
> So, I think we can set NULL to sock->sk in sk_common_release().
Thanks for the explanation. Makes sense. I'll spin up a v2 with this
(and try to test it as well).
>
> > Secondly, I was put off by this
> > comment (which I don't fully understand TBH) [1]
> >
> > On the other hand - in inet/inet6_create() we definitely know that the
> > object would be freed, because we just created that.
> >
> > But if someone more familiar with the code confirms it is
> > better/possible to do in sk_common_release(), I'm happy to adjust and
> > it would be cleaner indeed.
> >
> > > ---8<---
> > > diff --git a/net/core/sock.c b/net/core/sock.c
> > > index 8629f9aecf91..bbc94954d9bf 100644
> > > --- a/net/core/sock.c
> > > +++ b/net/core/sock.c
> > > @@ -3754,6 +3754,9 @@ void sk_common_release(struct sock *sk)
> > > * until the last reference will be released.
> > > */
> > >
> > > + if (sk->sk_socket)
> > > + sk->sk_socket->sk = NULL;
> > > +
> > > sock_orphan(sk);
> > >
> > > xfrm_sk_free_policy(sk);
> > > ---8<---
> >
> > [1]: https://elixir.bootlin.com/linux/v6.10-rc3/source/include/net/sock.h#L1985
>