KMSAN (KernelMemorySanitizer, a new error detection tool) reports use of
uninitialized memory in packet_bind_spkt():
==================================================================
BUG: KMSAN: use of unitialized memory
CPU: 0 PID: 1074 Comm: packet Not tainted 4.8.0-rc6+ #1891
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs
01/01/2011
0000000000000000 ffff88006b6dfc08 ffffffff82559ae8 ffff88006b6dfb48
ffffffff818a7c91 ffffffff85b9c870 0000000000000092 ffffffff85b9c550
0000000000000000 0000000000000092 00000000ec400911 0000000000000002
Call Trace:
[< inline >] __dump_stack lib/dump_stack.c:15
[<ffffffff82559ae8>] dump_stack+0x238/0x290 lib/dump_stack.c:51
[<ffffffff818a6626>] kmsan_report+0x276/0x2e0 mm/kmsan/kmsan.c:1003
[<ffffffff818a783b>] __msan_warning+0x5b/0xb0
mm/kmsan/kmsan_instr.c:424
[< inline >] strlen lib/string.c:484
[<ffffffff8259b58d>] strlcpy+0x9d/0x200 lib/string.c:144
[<ffffffff84b2eca4>] packet_bind_spkt+0x144/0x230
net/packet/af_packet.c:3132
[<ffffffff84242e4d>] SYSC_bind+0x40d/0x5f0 net/socket.c:1370
[<ffffffff84242a22>] SyS_bind+0x82/0xa0 net/socket.c:1356
[<ffffffff8515991b>] entry_SYSCALL_64_fastpath+0x13/0x8f
arch/x86/entry/entry_64.o:?
chained origin: 00000000eba00911
[<ffffffff810bb787>] save_stack_trace+0x27/0x50
arch/x86/kernel/stacktrace.c:67
[< inline >] kmsan_save_stack_with_flags mm/kmsan/kmsan.c:322
[< inline >] kmsan_save_stack mm/kmsan/kmsan.c:334
[<ffffffff818a59f8>] kmsan_internal_chain_origin+0x118/0x1e0
mm/kmsan/kmsan.c:527
[<ffffffff818a7773>] __msan_set_alloca_origin4+0xc3/0x130
mm/kmsan/kmsan_instr.c:380
[<ffffffff84242b69>] SYSC_bind+0x129/0x5f0 net/socket.c:1356
[<ffffffff84242a22>] SyS_bind+0x82/0xa0 net/socket.c:1356
[<ffffffff8515991b>] entry_SYSCALL_64_fastpath+0x13/0x8f
arch/x86/entry/entry_64.o:?
origin description: ----address@SYSC_bind (origin=00000000eb400911)
==================================================================
(the line numbers are relative to 4.8-rc6, but the bug persists
upstream)
, when I run the following program as root:
=====================================
#include <string.h>
#include <sys/socket.h>
#include <netpacket/packet.h>
#include <net/ethernet.h>
int main() {
struct sockaddr addr;
memset(&addr, 0xff, sizeof(addr));
addr.sa_family = AF_PACKET;
int fd = socket(PF_PACKET, SOCK_PACKET, htons(ETH_P_ALL));
bind(fd, &addr, sizeof(addr));
return 0;
}
=====================================
This happens because addr.sa_data copied from the userspace is not
zero-terminated, and copying it with strlcpy() in packet_bind_spkt()
results in calling strlen() on the kernel copy of that non-terminated
buffer.
Signed-off-by: Alexander Potapenko <[email protected]>
---
Changes since v3:
- addressed comments by Eric Dumazet (avoid using constants,
use memcpy() instead of strncpy())
---
net/packet/af_packet.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 2bd0d1949312..a0dbe7ca8f72 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -3103,7 +3103,7 @@ static int packet_bind_spkt(struct socket *sock, struct sockaddr *uaddr,
int addr_len)
{
struct sock *sk = sock->sk;
- char name[15];
+ char name[sizeof(uaddr->sa_data) + 1];
/*
* Check legality
@@ -3111,7 +3111,11 @@ static int packet_bind_spkt(struct socket *sock, struct sockaddr *uaddr,
if (addr_len != sizeof(struct sockaddr))
return -EINVAL;
- strlcpy(name, uaddr->sa_data, sizeof(name));
+ /* uaddr->sa_data comes from the userspace, it's not guaranteed to be
+ * zero-terminated.
+ */
+ memcpy(name, uaddr->sa_data, sizeof(uaddr->sa_data));
+ name[sizeof(uaddr->sa_data)] = 0;
return packet_do_bind(sk, name, 0, pkt_sk(sk)->num);
}
--
2.11.0.483.g087da7b7c-goog
On Wed, 2017-03-01 at 12:57 +0100, Alexander Potapenko wrote:
> KMSAN (KernelMemorySanitizer, a new error detection tool) reports use of
> uninitialized memory in packet_bind_spkt():
...
> Signed-off-by: Alexander Potapenko <[email protected]>
> ---
> Changes since v3:
> - addressed comments by Eric Dumazet (avoid using constants,
> use memcpy() instead of strncpy())
> ---
Acked-by: Eric Dumazet <[email protected]>
On Wed, Mar 1, 2017 at 3:57 AM, Alexander Potapenko <[email protected]> wrote:
> This happens because addr.sa_data copied from the userspace is not
> zero-terminated, and copying it with strlcpy() in packet_bind_spkt()
> results in calling strlen() on the kernel copy of that non-terminated
> buffer.
Very similar to
commit b301f2538759933cf9ff1f7c4f968da72e3f0757
Author: Pablo Neira Ayuso <[email protected]>
Date: Thu Mar 24 21:29:53 2016 +0100
netfilter: x_tables: enforce nul-terminated table name from
getsockopt GET_ENTRIES
From: Alexander Potapenko <[email protected]>
Date: Wed, 1 Mar 2017 12:57:20 +0100
> KMSAN (KernelMemorySanitizer, a new error detection tool) reports use of
> uninitialized memory in packet_bind_spkt():
...
> This happens because addr.sa_data copied from the userspace is not
> zero-terminated, and copying it with strlcpy() in packet_bind_spkt()
> results in calling strlen() on the kernel copy of that non-terminated
> buffer.
>
> Signed-off-by: Alexander Potapenko <[email protected]>
> ---
> Changes since v3:
> - addressed comments by Eric Dumazet (avoid using constants,
> use memcpy() instead of strncpy())
Applied and queued up for -stable.