Good afternoon,
After recently receiving a bug report from Syzbot [0] which was raised
specifically against the Android v5.10 kernel, I spent some time
trying to get to the crux. Firstly I reproduced the issue on the
reported kernel, then did the same using the latest release kernel
v5.16.
The full kernel trace can be seen below at [1].
I managed to seemingly bisect the issue down to commit:
60263d5889e6d ("iomap: fall back to buffered writes for invalidation failures")
Although it appears to be the belief of the Filesystem community that
this is likely not the cause of the issue and should therefore not be
reverted.
It took quite some time, but I managed to strip down the reported
kernel config (which was very large) down to x86_defconfig plus only a
few additional config symbols. Most of which are platform (qemu in
this case) config options the other is KASAN, required to successfully
reproduce this:
CONFIG_HYPERVISOR_GUEST=y
CONFIG_PARAVIRT=y
CONFIG_PARAVIRT_DEBUG=y
CONFIG_PARAVIRT_SPINLOCKS=y
CONFIG_KASAN=y
The (most likely non-optimised) qemu command currently being used is:
qemu-system-x86_64 -smp 8 -m 16G -enable-kvm -cpu max,migratable=off -no-reboot \
-kernel ${BUILDDIR}/arch/x86/boot/bzImage -nographic \
-hda ${IMAGEDIR}/wheezy-auto-repro.img \
-chardev stdio,id=char0,mux=on,logfile=serial.out,signal=off \
-serial chardev:char0 -mon chardev=char0 \
-append "root=/dev/sda rw console=ttyS0"
Darrick seems to suggest that:
"The BUG report came from page_buffers failing to find any buffer heads
attached to the page."
If the reproducer, also massively stripped down from the original
report, would be of any use to you, it can be found further down at
[2].
I don't how true this is, but it is my current belief that user-space
should not be able to force the kernel to BUG. This seems to be a
temporary DoS issue. So although not a critically serious security
problem involved memory leakage or data corruption, it could
potentially cause a nuisance if not rectified.
Any well meaning help with this would be gratefully received.
Kind regards,
Lee
[0] https://syzkaller.appspot.com/bug?extid=41c966bf0729a530bd8d
[1]
[ 15.200920] Page cache invalidation failure on direct I/O. Possible data corruption due to collision with buffered I/O!
[ 15.215877] File: /syzkaller.IsS3Yc/0/bus PID: 1497 Comm: repro
[ 16.718970] Page cache invalidation failure on direct I/O. Possible data corruption due to collision with buffered I/O!
[ 16.734250] File: /syzkaller.IsS3Yc/5/bus PID: 1512 Comm: repro
[ 17.013871] Page cache invalidation failure on direct I/O. Possible data corruption due to collision with buffered I/O!
[ 17.028193] File: /syzkaller.IsS3Yc/6/bus PID: 1515 Comm: repro
[ 17.320498] Page cache invalidation failure on direct I/O. Possible data corruption due to collision with buffered I/O!
[ 17.336115] File: /syzkaller.IsS3Yc/7/bus PID: 1518 Comm: repro
[ 17.617921] Page cache invalidation failure on direct I/O. Possible data corruption due to collision with buffered I/O!
[ 17.633063] File: /syzkaller.IsS3Yc/8/bus PID: 1521 Comm: repro
[ 18.527260] Page cache invalidation failure on direct I/O. Possible data corruption due to collision with buffered I/O!
[ 18.544236] File: /syzkaller.IsS3Yc/11/bus PID: 1530 Comm: repro
[ 18.810347] Page cache invalidation failure on direct I/O. Possible data corruption due to collision with buffered I/O!
[ 18.824721] File: /syzkaller.IsS3Yc/12/bus PID: 1533 Comm: repro
[ 19.099315] Page cache invalidation failure on direct I/O. Possible data corruption due to collision with buffered I/O!
[ 19.114151] File: /syzkaller.IsS3Yc/13/bus PID: 1536 Comm: repro
[ 19.403882] Page cache invalidation failure on direct I/O. Possible data corruption due to collision with buffered I/O!
[ 19.418467] File: /syzkaller.IsS3Yc/14/bus PID: 1539 Comm: repro
[ 19.703934] Page cache invalidation failure on direct I/O. Possible data corruption due to collision with buffered I/O!
[ 19.718400] File: /syzkaller.IsS3Yc/15/bus PID: 1542 Comm: repro
[ 26.533129] ------------[ cut here ]------------
[ 26.540473] WARNING: CPU: 1 PID: 1612 at fs/ext4/inode.c:3576 ext4_set_page_dirty+0xaf/0xc0
[ 26.553171] Modules linked in:
[ 26.557354] CPU: 1 PID: 1612 Comm: repro Not tainted 5.16.0+ #169
[ 26.565238] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014
[ 26.576182] RIP: 0010:ext4_set_page_dirty+0xaf/0xc0
[ 26.583077] Code: 4c 89 ff e8 e3 86 e7 ff 49 f7 07 00 20 00 00 74 19 4c 89 ff 5b 41 5e 41 5f e9 8d 05 f0 ff 48 83 c0 ff 48 89 c3 e9 76 ff ff ff <0f> 0b eb e3 48 83 c0 ff 48 89 c3 eb 9e 0f 0b eb b8 55 48 89 e5 41
[ 26.607402] RSP: 0018:ffff88810f4ffa10 EFLAGS: 00010246
[ 26.614646] RAX: ffffea00043bc687 RBX: ffffea00043bc680 RCX: ffffffff9913f86d
[ 26.625115] RDX: 0000000000000000 RSI: dffffc0000000000 RDI: ffffea00043bc680
[ 26.635137] RBP: 0000000000000400 R08: dffffc0000000000 R09: fffff940008778d1
[ 26.644923] R10: fffff940008778d1 R11: 0000000000000000 R12: ffff88810e14c000
[ 26.654807] R13: ffffea00043bc680 R14: ffffea00043bc688 R15: ffffea00043bc680
[ 26.664812] FS: 00007f27c16d6640(0000) GS:ffff8883ef440000(0000) knlGS:0000000000000000
[ 26.676238] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 26.684212] CR2: 000000000049b3a8 CR3: 000000010f7a6005 CR4: 0000000000370ee0
[ 26.693896] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 26.703778] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 26.714238] Call Trace:
[ 26.717987] <TASK>
[ 26.721105] folio_mark_dirty+0x72/0xa0
[ 26.726455] set_page_dirty_lock+0x4a/0x70
[ 26.732426] unpin_user_pages_dirty_lock+0x101/0x1d0
[ 26.739369] process_vm_rw_single_vec+0x2f4/0x3c0
[ 26.745707] ? process_vm_rw+0x4d0/0x4d0
[ 26.751454] ? mm_access+0xe1/0x120
[ 26.756495] process_vm_rw+0x2fd/0x4d0
[ 26.762431] ? __ia32_sys_process_vm_writev+0x80/0x80
[ 26.769780] ? preempt_count_sub+0xf/0xc0
[ 26.775021] ? folio_add_lru+0xea/0x110
[ 26.780260] ? preempt_count_sub+0xf/0xc0
[ 26.786062] ? _raw_spin_unlock+0x2e/0x50
[ 26.791676] ? __handle_mm_fault+0x14a7/0x1970
[ 26.797550] ? handle_mm_fault+0x1d0/0x1d0
[ 26.802981] ? up_read+0x6f/0x180
[ 26.807430] ? down_read_trylock+0x13f/0x190
[ 26.813252] ? down_write_trylock+0x130/0x130
[ 26.818935] ? handle_mm_fault+0x160/0x1d0
[ 26.824454] ? do_kern_addr_fault+0x130/0x130
[ 26.830695] __x64_sys_process_vm_writev+0x71/0x80
[ 26.837270] do_syscall_64+0x43/0x90
[ 26.842134] entry_SYSCALL_64_after_hwframe+0x44/0xae
[ 26.848994] RIP: 0033:0x44c849
[ 26.853311] Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 c1 14 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
[ 26.877911] RSP: 002b:00007f27c16d6168 EFLAGS: 00000216 ORIG_RAX: 0000000000000137
[ 26.887953] RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 000000000044c849
[ 26.897571] RDX: 0000000000000001 RSI: 0000000020c22000 RDI: 0000000000000076
[ 26.907068] RBP: 00007f27c16d61a0 R08: 0000000000000001 R09: 0000000000000000
[ 26.916433] R10: 0000000020c22fa0 R11: 0000000000000216 R12: 00007ffd3062431e
[ 26.927113] R13: 00007ffd3062431f R14: 0000000000000000 R15: 00007f27c16d6640
[ 26.936755] </TASK>
[ 26.939785] ---[ end trace 42b5bb79157828eb ]---
[ 27.160243] ------------[ cut here ]------------
[ 27.166572] kernel BUG at fs/ext4/inode.c:2620!
[ 27.173362] invalid opcode: 0000 [#1] PREEMPT SMP KASAN PTI
[ 27.180459] CPU: 1 PID: 1616 Comm: repro Tainted: G W 5.16.0+ #169
[ 27.190304] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014
[ 27.201112] RIP: 0010:mpage_prepare_extent_to_map+0x573/0x580
[ 27.208692] Code: 08 14 00 00 00 00 65 48 8b 04 25 28 00 00 00 48 3b 84 24 40 01 00 00 75 15 89 d8 48 8d 65 d8 5b 41 5c 41 5d 41 5e 41 5f 5d c3 <0f> 0b 0f 0b e8 04 39 15 01 0f 1f 40 00 55 48 89 e5 41 57 41 56 41
[ 27.232612] RSP: 0018:ffff88810f7e6b60 EFLAGS: 00010246
[ 27.239348] RAX: ffffea00043b4fc7 RBX: 0000000000000067 RCX: ffffffff9913ea61
[ 27.248720] RDX: 0000000000000000 RSI: dffffc0000000000 RDI: ffffea00043b4fc0
[ 27.257899] RBP: ffff88810f7e6cf0 R08: dffffc0000000000 R09: fffff940008769f9
[ 27.266846] R10: fffff940008769f9 R11: 0000000000000000 R12: 0000000000000000
[ 27.276050] R13: ffff88810f7e6be0 R14: ffffea00043b4fc0 R15: ffff88810f7e6f58
[ 27.285119] FS: 00007f27c16d6640(0000) GS:ffff8883ef440000(0000) knlGS:0000000000000000
[ 27.295466] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 27.302935] CR2: 0000000020002002 CR3: 000000010cb70006 CR4: 0000000000370ee0
[ 27.312837] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 27.322697] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 27.332451] Call Trace:
[ 27.336060] <TASK>
[ 27.339164] ? ext4_iomap_swap_activate+0x10/0x10
[ 27.346171] ? preempt_count_sub+0xf/0xc0
[ 27.352456] ? page_writeback_cpu_online+0x1f0/0x1f0
[ 27.359598] ? ext4_init_io_end+0x18/0x90
[ 27.365427] ? kmem_cache_alloc+0xf2/0x200
[ 27.371638] ext4_writepages+0x823/0x1c50
[ 27.377047] ? kernel_text_address+0xa8/0xc0
[ 27.382587] ? unwind_get_return_address+0x25/0x40
[ 27.388649] ? __rcu_read_unlock+0x8d/0x320
[ 27.394134] ? __rcu_read_lock+0x20/0x20
[ 27.399094] ? preempt_count_sub+0xf/0xc0
[ 27.404220] ? ext4_readpage+0x110/0x110
[ 27.409494] ? stack_trace_save+0x120/0x120
[ 27.414838] ? __is_insn_slot_addr+0x58/0x60
[ 27.420186] ? kernel_text_address+0xa8/0xc0
[ 27.425531] ? __kernel_text_address+0x9/0x40
[ 27.431355] ? unwind_get_return_address+0x25/0x40
[ 27.437415] ? stack_trace_save+0xdb/0x120
[ 27.442722] ? stack_trace_snprint+0xc0/0xc0
[ 27.448310] do_writepages+0x20b/0x3a0
[ 27.453245] ? __kasan_slab_alloc+0x43/0xb0
[ 27.458532] ? filter_irq_stacks+0x3d/0x80
[ 27.463792] ? __writepage+0xb0/0xb0
[ 27.468366] ? __iomap_dio_rw+0x1c2/0xec0
[ 27.473579] ? iomap_dio_rw+0x5/0x30
[ 27.478152] ? ext4_file_write_iter+0x8a8/0xde0
[ 27.484091] ? do_iter_readv_writev+0x2ce/0x360
[ 27.490002] ? do_iter_write+0x109/0x370
[ 27.495400] ? iter_file_splice_write+0x4b6/0x770
[ 27.501658] ? direct_splice_actor+0x7b/0x90
[ 27.507225] ? splice_direct_to_actor+0x309/0x570
[ 27.513487] ? do_splice_direct+0x172/0x230
[ 27.519352] ? do_sendfile+0x567/0x960
[ 27.524605] ? __x64_sys_sendfile64+0x104/0x150
[ 27.531035] ? do_syscall_64+0x43/0x90
[ 27.536259] ? entry_SYSCALL_64_after_hwframe+0x44/0xae
[ 27.543606] ? do_syscall_64+0x43/0x90
[ 27.548942] ? entry_SYSCALL_64_after_hwframe+0x44/0xae
[ 27.556281] ? _raw_spin_lock+0x120/0x120
[ 27.561984] ? __ext4_handle_dirty_metadata+0x22d/0x510
[ 27.569186] filemap_write_and_wait_range+0x200/0x230
[ 27.576185] ? filemap_range_needs_writeback+0x400/0x400
[ 27.583632] ? ext4_mark_iloc_dirty+0x66c/0x6b0
[ 27.589986] ? kmem_cache_alloc_trace+0xe7/0x230
[ 27.596373] ? __iomap_dio_rw+0x1c2/0xec0
[ 27.601967] __iomap_dio_rw+0x525/0xec0
[ 27.609616] ? jbd2_journal_stop+0x481/0x5b0
[ 27.615606] ? iomap_dio_complete+0x2a0/0x2a0
[ 27.622054] ? generic_update_time+0xde/0x130
[ 27.628225] ? __mnt_drop_write_file+0xd/0x60
[ 27.634306] ? file_update_time+0x1cd/0x210
[ 27.640161] ? kernel_text_address+0xa8/0xc0
[ 27.646114] ? file_remove_privs+0x2b0/0x2b0
[ 27.652278] iomap_dio_rw+0x5/0x30
[ 27.657149] ext4_file_write_iter+0x8a8/0xde0
[ 27.663323] ? ext4_file_read_iter+0x1e0/0x1e0
[ 27.669800] ? ____kasan_kmalloc+0xd1/0xf0
[ 27.675676] ? direct_splice_actor+0x7b/0x90
[ 27.681778] ? splice_direct_to_actor+0x309/0x570
[ 27.688357] ? do_splice_direct+0x172/0x230
[ 27.694256] ? do_sendfile+0x567/0x960
[ 27.699605] ? __x64_sys_sendfile64+0x104/0x150
[ 27.706129] ? entry_SYSCALL_64_after_hwframe+0x44/0xae
[ 27.713462] do_iter_readv_writev+0x2ce/0x360
[ 27.719894] ? generic_file_rw_checks+0xd0/0xd0
[ 27.726446] ? memcpy+0x3c/0x60
[ 27.731234] ? security_file_permission+0x47/0x270
[ 27.738026] do_iter_write+0x109/0x370
[ 27.743417] iter_file_splice_write+0x4b6/0x770
[ 27.749824] ? splice_from_pipe+0x170/0x170
[ 27.755630] ? generic_file_splice_read+0x2d0/0x380
[ 27.765041] ? splice_shrink_spd+0x40/0x40
[ 27.770668] ? is_mmconf_reserved+0x240/0x240
[ 27.776487] ? kcalloc+0x1b/0x20
[ 27.780737] ? splice_from_pipe+0x170/0x170
[ 27.786278] direct_splice_actor+0x7b/0x90
[ 27.791885] splice_direct_to_actor+0x309/0x570
[ 27.797680] ? do_splice_direct+0x230/0x230
[ 27.803067] ? pipe_to_sendpage+0x1b0/0x1b0
[ 27.808395] ? security_file_permission+0x47/0x270
[ 27.814761] do_splice_direct+0x172/0x230
[ 27.819842] ? splice_direct_to_actor+0x570/0x570
[ 27.825936] ? security_file_permission+0x47/0x270
[ 27.832354] do_sendfile+0x567/0x960
[ 27.837426] ? do_pwritev+0x3d0/0x3d0
[ 27.842258] ? __se_sys_futex+0x1b1/0x2c0
[ 27.847619] ? restore_fpregs_from_fpstate+0xc4/0x190
[ 27.854277] __x64_sys_sendfile64+0x104/0x150
[ 27.859919] ? __ia32_sys_sendfile+0x170/0x170
[ 27.865622] ? switch_fpu_return+0x97/0x120
[ 27.871204] do_syscall_64+0x43/0x90
[ 27.875661] entry_SYSCALL_64_after_hwframe+0x44/0xae
[ 27.882673] RIP: 0033:0x44c849
[ 27.887077] Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 c1 14 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
[ 27.911882] RSP: 002b:00007f27c16d6178 EFLAGS: 00000203 ORIG_RAX: 0000000000000028
[ 27.921306] RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 000000000044c849
[ 27.930587] RDX: 0000000000000000 RSI: 0000000000000004 RDI: 0000000000000003
[ 27.939877] RBP: 00007f27c16d61a0 R08: 0000000000000000 R09: 0000000000000000
[ 27.949975] R10: 0000000080000005 R11: 0000000000000203 R12: 00007ffd3062431e
[ 27.959298] R13: 00007ffd3062431f R14: 0000000000000000 R15: 00007f27c16d6640
[ 27.968616] </TASK>
[ 27.971668] Modules linked in:
[ 27.975922] ---[ end trace 42b5bb79157828ec ]---
[ 27.982710] RIP: 0010:mpage_prepare_extent_to_map+0x573/0x580
[ 27.990558] Code: 08 14 00 00 00 00 65 48 8b 04 25 28 00 00 00 48 3b 84 24 40 01 00 00 75 15 89 d8 48 8d 65 d8 5b 41 5c 41 5d 41 5e 41 5f 5d c3 <0f> 0b 0f 0b e8 04 39 15 01 0f 1f 40 00 55 48 89 e5 41 57 41 56 41
[ 28.015009] RSP: 0018:ffff88810f7e6b60 EFLAGS: 00010246
[ 28.021763] RAX: ffffea00043b4fc7 RBX: 0000000000000067 RCX: ffffffff9913ea61
[ 28.031325] RDX: 0000000000000000 RSI: dffffc0000000000 RDI: ffffea00043b4fc0
[ 28.040622] RBP: ffff88810f7e6cf0 R08: dffffc0000000000 R09: fffff940008769f9
[ 28.050140] R10: fffff940008769f9 R11: 0000000000000000 R12: 0000000000000000
[ 28.059313] R13: ffff88810f7e6be0 R14: ffffea00043b4fc0 R15: ffff88810f7e6f58
[ 28.068502] FS: 00007f27c16d6640(0000) GS:ffff8883ef440000(0000) knlGS:0000000000000000
[ 28.079454] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 28.087279] CR2: 0000000020002002 CR3: 000000010cb70006 CR4: 0000000000370ee0
[ 28.096763] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 28.105974] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[2]
// https://syzkaller.appspot.com/bug?id=906354c4596539d9561ee6cb6d8c54cda38fc3c2
// autogenerated by syzkaller (https://github.com/google/syzkaller)
#define _GNU_SOURCE
#include <arpa/inet.h>
#include <dirent.h>
#include <endian.h>
#include <errno.h>
#include <fcntl.h>
#include <net/if.h>
#include <net/if_arp.h>
#include <netinet/in.h>
#include <pthread.h>
#include <sched.h>
#include <signal.h>
#include <stdarg.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/ioctl.h>
#include <sys/mount.h>
#include <sys/prctl.h>
#include <sys/resource.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/syscall.h>
#include <sys/time.h>
#include <sys/types.h>
#include <sys/uio.h>
#include <sys/wait.h>
#include <time.h>
#include <unistd.h>
#include <linux/capability.h>
#include <linux/futex.h>
#include <linux/genetlink.h>
#include <linux/if_addr.h>
#include <linux/if_ether.h>
#include <linux/if_link.h>
#include <linux/if_tun.h>
#include <linux/in6.h>
#include <linux/ip.h>
#include <linux/neighbour.h>
#include <linux/net.h>
#include <linux/netlink.h>
#include <linux/rtnetlink.h>
#include <linux/tcp.h>
#include <linux/veth.h>
static void sleep_ms(uint64_t ms)
{
usleep(ms * 1000);
}
static uint64_t current_time_ms(void)
{
struct timespec ts;
if (clock_gettime(CLOCK_MONOTONIC, &ts))
exit(1);
return (uint64_t)ts.tv_sec * 1000 + (uint64_t)ts.tv_nsec / 1000000;
}
static void use_temporary_dir(void)
{
char tmpdir_template[] = "./syzkaller.XXXXXX";
char* tmpdir = mkdtemp(tmpdir_template);
if (!tmpdir)
exit(1);
if (chmod(tmpdir, 0777))
exit(1);
if (chdir(tmpdir))
exit(1);
}
static void thread_start(void* (*fn)(void*), void* arg)
{
pthread_t th;
pthread_attr_t attr;
pthread_attr_init(&attr);
pthread_attr_setstacksize(&attr, 128 << 10);
int i = 0;
for (; i < 100; i++) {
if (pthread_create(&th, &attr, fn, arg) == 0) {
pthread_attr_destroy(&attr);
return;
}
if (errno == EAGAIN) {
usleep(50);
continue;
}
break;
}
exit(1);
}
typedef struct {
int state;
} event_t;
static void event_init(event_t* ev)
{
ev->state = 0;
}
static void event_reset(event_t* ev)
{
ev->state = 0;
}
static void event_set(event_t* ev)
{
if (ev->state)
exit(1);
__atomic_store_n(&ev->state, 1, __ATOMIC_RELEASE);
syscall(SYS_futex, &ev->state, FUTEX_WAKE | FUTEX_PRIVATE_FLAG, 1000000);
}
static void event_wait(event_t* ev)
{
while (!__atomic_load_n(&ev->state, __ATOMIC_ACQUIRE))
syscall(SYS_futex, &ev->state, FUTEX_WAIT | FUTEX_PRIVATE_FLAG, 0, 0);
}
static int event_isset(event_t* ev)
{
return __atomic_load_n(&ev->state, __ATOMIC_ACQUIRE);
}
static int event_timedwait(event_t* ev, uint64_t timeout)
{
uint64_t start = current_time_ms();
uint64_t now = start;
for (;;) {
uint64_t remain = timeout - (now - start);
struct timespec ts;
ts.tv_sec = remain / 1000;
ts.tv_nsec = (remain % 1000) * 1000 * 1000;
syscall(SYS_futex, &ev->state, FUTEX_WAIT | FUTEX_PRIVATE_FLAG, 0, &ts);
if (__atomic_load_n(&ev->state, __ATOMIC_ACQUIRE))
return 1;
now = current_time_ms();
if (now - start > timeout)
return 0;
}
}
#define IFLA_IPVLAN_FLAGS 2
#define IPVLAN_MODE_L3S 2
#undef IPVLAN_F_VEPA
#define IPVLAN_F_VEPA 2
#define TUN_IFACE "syz_tun"
#define LOCAL_MAC 0xaaaaaaaaaaaa
#define REMOTE_MAC 0xaaaaaaaaaabb
#define LOCAL_IPV4 "172.20.20.170"
#define REMOTE_IPV4 "172.20.20.187"
#define LOCAL_IPV6 "fe80::aa"
#define REMOTE_IPV6 "fe80::bb"
#define IFF_NAPI 0x0010
#define DEVLINK_FAMILY_NAME "devlink"
#define DEVLINK_CMD_PORT_GET 5
#define DEVLINK_ATTR_BUS_NAME 1
#define DEVLINK_ATTR_DEV_NAME 2
#define DEVLINK_ATTR_NETDEV_NAME 7
#define DEV_IPV4 "172.20.20.%d"
#define DEV_IPV6 "fe80::%02x"
#define DEV_MAC 0x00aaaaaaaaaa
#define WG_GENL_NAME "wireguard"
enum wg_cmd {
WG_CMD_GET_DEVICE,
WG_CMD_SET_DEVICE,
};
enum wgdevice_attribute {
WGDEVICE_A_UNSPEC,
WGDEVICE_A_IFINDEX,
WGDEVICE_A_IFNAME,
WGDEVICE_A_PRIVATE_KEY,
WGDEVICE_A_PUBLIC_KEY,
WGDEVICE_A_FLAGS,
WGDEVICE_A_LISTEN_PORT,
WGDEVICE_A_FWMARK,
WGDEVICE_A_PEERS,
};
enum wgpeer_attribute {
WGPEER_A_UNSPEC,
WGPEER_A_PUBLIC_KEY,
WGPEER_A_PRESHARED_KEY,
WGPEER_A_FLAGS,
WGPEER_A_ENDPOINT,
WGPEER_A_PERSISTENT_KEEPALIVE_INTERVAL,
WGPEER_A_LAST_HANDSHAKE_TIME,
WGPEER_A_RX_BYTES,
WGPEER_A_TX_BYTES,
WGPEER_A_ALLOWEDIPS,
WGPEER_A_PROTOCOL_VERSION,
};
enum wgallowedip_attribute {
WGALLOWEDIP_A_UNSPEC,
WGALLOWEDIP_A_FAMILY,
WGALLOWEDIP_A_IPADDR,
WGALLOWEDIP_A_CIDR_MASK,
};
#define MAX_FDS 30
#define XT_TABLE_SIZE 1536
#define XT_MAX_ENTRIES 10
struct xt_counters {
uint64_t pcnt, bcnt;
};
struct ipt_getinfo {
char name[32];
unsigned int valid_hooks;
unsigned int hook_entry[5];
unsigned int underflow[5];
unsigned int num_entries;
unsigned int size;
};
struct ipt_get_entries {
char name[32];
unsigned int size;
uint64_t entrytable[XT_TABLE_SIZE / sizeof(uint64_t)];
};
struct ipt_replace {
char name[32];
unsigned int valid_hooks;
unsigned int num_entries;
unsigned int size;
unsigned int hook_entry[5];
unsigned int underflow[5];
unsigned int num_counters;
struct xt_counters* counters;
uint64_t entrytable[XT_TABLE_SIZE / sizeof(uint64_t)];
};
struct ipt_table_desc {
const char* name;
struct ipt_getinfo info;
struct ipt_replace replace;
};
#define IPT_BASE_CTL 64
#define IPT_SO_SET_REPLACE (IPT_BASE_CTL)
#define IPT_SO_GET_INFO (IPT_BASE_CTL)
#define IPT_SO_GET_ENTRIES (IPT_BASE_CTL + 1)
struct arpt_getinfo {
char name[32];
unsigned int valid_hooks;
unsigned int hook_entry[3];
unsigned int underflow[3];
unsigned int num_entries;
unsigned int size;
};
struct arpt_get_entries {
char name[32];
unsigned int size;
uint64_t entrytable[XT_TABLE_SIZE / sizeof(uint64_t)];
};
struct arpt_replace {
char name[32];
unsigned int valid_hooks;
unsigned int num_entries;
unsigned int size;
unsigned int hook_entry[3];
unsigned int underflow[3];
unsigned int num_counters;
struct xt_counters* counters;
uint64_t entrytable[XT_TABLE_SIZE / sizeof(uint64_t)];
};
#define ARPT_BASE_CTL 96
#define ARPT_SO_SET_REPLACE (ARPT_BASE_CTL)
#define ARPT_SO_GET_INFO (ARPT_BASE_CTL)
#define ARPT_SO_GET_ENTRIES (ARPT_BASE_CTL + 1)
static void loop();
static int wait_for_loop(int pid)
{
if (pid < 0)
exit(1);
int status = 0;
while (waitpid(-1, &status, __WALL) != pid) {
}
return WEXITSTATUS(status);
}
static int do_sandbox_none(void)
{
if (unshare(CLONE_NEWPID)) {
}
int pid = fork();
if (pid != 0)
return wait_for_loop(pid);
if (unshare(CLONE_NEWNET)) {
}
loop();
exit(1);
}
#define FS_IOC_SETFLAGS _IOW('f', 2, long)
static void remove_dir(const char* dir)
{
int iter = 0;
DIR* dp = 0;
retry:
while (umount2(dir, MNT_DETACH | UMOUNT_NOFOLLOW) == 0) {
}
dp = opendir(dir);
if (dp == NULL) {
if (errno == EMFILE) {
exit(1);
}
exit(1);
}
struct dirent* ep = 0;
while ((ep = readdir(dp))) {
if (strcmp(ep->d_name, ".") == 0 || strcmp(ep->d_name, "..") == 0)
continue;
char filename[FILENAME_MAX];
snprintf(filename, sizeof(filename), "%s/%s", dir, ep->d_name);
while (umount2(filename, MNT_DETACH | UMOUNT_NOFOLLOW) == 0) {
}
struct stat st;
if (lstat(filename, &st))
exit(1);
if (S_ISDIR(st.st_mode)) {
remove_dir(filename);
continue;
}
int i;
for (i = 0;; i++) {
if (unlink(filename) == 0)
break;
if (errno == EPERM) {
int fd = open(filename, O_RDONLY);
if (fd != -1) {
long flags = 0;
if (ioctl(fd, FS_IOC_SETFLAGS, &flags) == 0) {
}
close(fd);
continue;
}
}
if (errno == EROFS) {
break;
}
if (errno != EBUSY || i > 100)
exit(1);
if (umount2(filename, MNT_DETACH | UMOUNT_NOFOLLOW))
exit(1);
}
}
closedir(dp);
for (int i = 0;; i++) {
if (rmdir(dir) == 0)
break;
if (i < 100) {
if (errno == EPERM) {
int fd = open(dir, O_RDONLY);
if (fd != -1) {
long flags = 0;
if (ioctl(fd, FS_IOC_SETFLAGS, &flags) == 0) {
}
close(fd);
continue;
}
}
if (errno == EROFS) {
break;
}
if (errno == EBUSY) {
if (umount2(dir, MNT_DETACH | UMOUNT_NOFOLLOW))
exit(1);
continue;
}
if (errno == ENOTEMPTY) {
if (iter < 100) {
iter++;
goto retry;
}
}
}
exit(1);
}
}
static void kill_and_wait(int pid, int* status)
{
kill(-pid, SIGKILL);
kill(pid, SIGKILL);
for (int i = 0; i < 100; i++) {
if (waitpid(-1, status, WNOHANG | __WALL) == pid)
return;
usleep(1000);
}
DIR* dir = opendir("/sys/fs/fuse/connections");
if (dir) {
for (;;) {
struct dirent* ent = readdir(dir);
if (!ent)
break;
if (strcmp(ent->d_name, ".") == 0 || strcmp(ent->d_name, "..") == 0)
continue;
char abort[300];
snprintf(abort, sizeof(abort), "/sys/fs/fuse/connections/%s/abort",
ent->d_name);
int fd = open(abort, O_WRONLY);
if (fd == -1) {
continue;
}
if (write(fd, abort, 1) < 0) {
}
close(fd);
}
closedir(dir);
} else {
}
while (waitpid(-1, status, __WALL) != pid) {
}
}
static void close_fds()
{
for (int fd = 3; fd < MAX_FDS; fd++)
close(fd);
}
struct thread_t {
int created, call;
event_t ready, done;
};
static struct thread_t threads[16];
static void execute_call(int call);
static int running;
static void* thr(void* arg)
{
struct thread_t* th = (struct thread_t*)arg;
for (;;) {
event_wait(&th->ready);
event_reset(&th->ready);
execute_call(th->call);
__atomic_fetch_sub(&running, 1, __ATOMIC_RELAXED);
event_set(&th->done);
}
return 0;
}
static void execute_one(void)
{
int i, call, thread;
for (call = 0; call < 10; call++) {
for (thread = 0; thread < (int)(sizeof(threads) / sizeof(threads[0]));
thread++) {
struct thread_t* th = &threads[thread];
if (!th->created) {
th->created = 1;
event_init(&th->ready);
event_init(&th->done);
event_set(&th->done);
thread_start(thr, th);
}
if (!event_isset(&th->done))
continue;
event_reset(&th->done);
th->call = call;
__atomic_fetch_add(&running, 1, __ATOMIC_RELAXED);
event_set(&th->ready);
event_timedwait(&th->done, 50);
break;
}
}
for (i = 0; i < 100 && __atomic_load_n(&running, __ATOMIC_RELAXED); i++)
sleep_ms(1);
close_fds();
}
static void execute_one(void);
#define WAIT_FLAGS __WALL
static void loop(void)
{
int iter = 0;
for (;; iter++) {
char cwdbuf[32];
sprintf(cwdbuf, "./%d", iter);
if (mkdir(cwdbuf, 0777))
exit(1);
int pid = fork();
if (pid < 0)
exit(1);
if (pid == 0) {
if (chdir(cwdbuf))
exit(1);
execute_one();
exit(0);
}
int status = 0;
uint64_t start = current_time_ms();
for (;;) {
if (waitpid(-1, &status, WNOHANG | WAIT_FLAGS) == pid) {
break;
}
sleep_ms(1);
if (current_time_ms() - start < 5000)
continue;
kill_and_wait(pid, &status);
break;
}
remove_dir(cwdbuf);
}
}
uint64_t r[5] = {0xffffffffffffffff, 0xffffffffffffffff, 0xffffffffffffffff,
0xffffffffffffffff, 0x0};
void execute_call(int call)
{
intptr_t res = 0;
switch (call) {
case 0:
memcpy((void*)0x20000080, "./bus\000", 6);
res = syscall(__NR_open, 0x20000080ul, 0x14d842ul, 0ul);
if (res != -1)
r[0] = res;
break;
case 1:
memcpy((void*)0x20000000, "/proc/self/exe\000", 15);
res = syscall(__NR_openat, 0xffffff9c, 0x20000000ul, 0ul, 0ul);
if (res != -1)
r[1] = res;
break;
case 2:
memcpy((void*)0x20002000, "./bus\000", 6);
res = syscall(__NR_open, 0x20002000ul, 0x143042ul, 0ul);
if (res != -1)
r[2] = res;
break;
case 3:
syscall(__NR_ftruncate, r[2], 0x2008002ul);
break;
case 4:
memcpy((void*)0x20000400, "./bus\000", 6);
res = syscall(__NR_open, 0x20000400ul, 0x14103eul, 0ul);
if (res != -1)
r[3] = res;
break;
case 5:
syscall(__NR_mmap, 0x20000000ul, 0x600000ul, 0x7ffffeul, 0x11ul, r[3], 0ul);
break;
case 6:
syscall(__NR_sendfile, r[0], r[1], 0ul, 0x80000005ul);
break;
case 7:
res = syscall(__NR_gettid);
if (res != -1)
r[4] = res;
break;
case 8:
*(uint64_t*)0x20c22000 = 0x2034afa4;
*(uint64_t*)0x20c22008 = 0x1f80;
*(uint64_t*)0x20c22fa0 = 0x20000080;
*(uint64_t*)0x20c22fa8 = 0x2034afa5;
syscall(__NR_process_vm_writev, r[4], 0x20c22000ul, 1ul, 0x20c22fa0ul, 1ul,
0ul);
break;
case 9:
syscall(__NR_sendfile, r[0], r[1], 0ul, 0x80000005ul);
break;
}
}
int main(void)
{
syscall(__NR_mmap, 0x1ffff000ul, 0x1000ul, 0ul, 0x32ul, -1, 0ul);
syscall(__NR_mmap, 0x20000000ul, 0x1000000ul, 7ul, 0x32ul, -1, 0ul);
syscall(__NR_mmap, 0x21000000ul, 0x1000ul, 0ul, 0x32ul, -1, 0ul);
use_temporary_dir();
do_sandbox_none();
return 0;
}
--
Lee Jones [李琼斯]
Principal Technical Lead - Developer Services
Linaro.org │ Open source software for Arm SoCs
Follow Linaro: Facebook | Twitter | Blog
On Thu, Feb 17, 2022 at 10:33:34PM -0800, John Hubbard wrote:
>
> Just a small thing I'll say once, to get it out of my system. No action
> required here, I just want it understood:
>
> Before commit 803e4572d7c5 ("mm/process_vm_access: set FOLL_PIN via
> pin_user_pages_remote()"), you would have written that like this:
>
> "process_vm_writev() is dirtying pages without properly warning the file
> system in advance..."
>
> Because, there were many callers that were doing this:
>
> get_user_pages*()
> ...use the pages...
>
> for_each_page() {
> set_page_dirty*()
> put_page()
> }
Sure, but that's not sufficient when modifying file-backed pages.
Previously, there was only two ways of modifying file-backed pages in
the page cache --- either using the write(2) system call, or when a
mmaped page is modified by the userspace.
In the case of write(2), the file system gets notified before the page
cache is modified by a call to the address operation's write_begin()
call, and after the page cache is modified, the address operation's
write_end() call lets the file system know that the modification is
done. After the write is done, the 30 second writeback timer is
triggered, and in the case of ext4's data=journalling mode, we close
the ext4 micro-transation (and therefore the time between write_begin
and write_end calls needs to be minimal); otherwise this can block
ext4 transactions.
In the case of a user page fault, the address operation's
page_mkwrite() is called, and at that point we will allocate any
blocks needed to back memory if necessary (in the case of delayed
allocation, file system space has to get reserved). The problem here
for remote access is that page_mkwrite() can block, and it can
potentially fail (e.g., with ENOSPC or ENOMEM). This is also why we
can't just add the page buffers and do the file system allocation in
set_page_dirty(), since set_page_dirty() isn't allowed to block.
One approach might be to make all of the pages writeable when
pin_user_pages_remote() is called. That that would mean that in the
case of remote access via process_vm_writev or RDMA, all of the blocks
will be allocated early. But that's probably better since at that
point the userspace code is in a position to receive the error when
setting up the RDMA memory, and we don't want to be asking the file
system to do block allocation when incoming data is coming in from
Infiniband or iWARP.
> I see that ext4_warning_inode() has rate limiting, but it doesn't look
> like it's really intended for a per-page rate. It looks like it is
> per-superblock (yes?), so I suspect one instance of this problem, with
> many pages involved, could hit the limit.
>
> Often, WARN_ON_ONCE() is used with per-page assertions. That's not great
> either, but it might be better here. OTOH, I have minimal experience
> with ext4_warning_inode() and maybe it really is just fine with per-page
> failure rates.
With the syzbot reproducer, we're not actually triggering the rate
limiter, since the ext4 warning is only getting hit a bit more than
once every 4 seconds. And I'm guessing that in the real world, people
aren't actually trying to do remote direct access to file-backed
memory, at least not using ext4, since that's an invitation to a
kernel crash, and we would have gotten user complaints. If some user
actually tries to use process_vm_writev for realsies, as opposed to a
random fuzzer or from a malicious program , we do want to warn them
about the potential data loss, so I'd prefer to warn once for each
inode --- but I'm not convinced that it's worth the effort.
Cheers,
- Ted
On Wed, Feb 23, 2022 at 04:44:07PM -0800, John Hubbard wrote:
>
> Actually...I can confirm that real customers really are doing *exactly*
> that! Despite the kernel crashes--because the crashes don't always
> happen unless you have a large (supercomputer-sized) installation. And
> even then it is not always root-caused properly.
Interesting. The syzbot reproducer triggers *reliably* on ext4 using
a 2 CPU qemu kernel running on a laptop, and it doesn't require root,
so it's reasonable that Lee is pushing for a fix --- even if for the
Android O or newer, Seccomp can probably prohibit trap
process_vm_writev(2), but it seems unfortunate if say, someone running
a Docker container could take down the entire host OS.
- Ted
On Wed, Feb 23, 2022 at 10:50:09PM -0500, Theodore Ts'o wrote:
> On Thu, Feb 24, 2022 at 12:48:42PM +1100, Dave Chinner wrote:
> > > Fair enough; on the other hand, we could also view this as making ext4
> > > more robust against buggy code in other subsystems, and while other
> > > file systems may be losing user data if they are actually trying to do
> > > remote memory access to file-backed memory, apparently other file
> > > systems aren't noticing and so they're not crashing.
> >
> > Oh, we've noticed them, no question about that. We've got bug
> > reports going back years for systems being crashed, triggering BUGs
> > and/or corrupting data on both XFS and ext4 filesystems due to users
> > trying to run RDMA applications with file backed pages.
>
> Is this issue causing XFS to crash? I didn't know that.
I have no idea if crashes nowdays - go back a few years before and
search for XFS BUGging out in ->invalidate_page (or was it
->release_page?) because of unexpected dirty pages. I think it could
also trigger BUGs in writeback when ->writepages tripped over a
dirty page without a delayed allocation mapping over the hole...
We were pretty aggressive about telling people reporting such issues
that they get to keep all the borken bits to themselves and to stop
wasting our time with unsolvable problems caused by their
broken-by-design RDMA applications. Hence people have largely
stopped bothering us with random filesystem crashes on systems using
RDMA on file-backed pages...
> I tried the Syzbot reproducer with XFS mounted, and it didn't trigger
> any crashes. I'm sure data was getting corrupted, but I figured I
> should bring ext4 to the XFS level of "at least we're not reliably
> killing the kernel".
Oh, well, good to know XFS didn't die a horrible death immediately.
Thanks for checking, Ted.
> On ext4, an unprivileged process can use process_vm_writev(2) to crash
> the system. I don't know how quickly we can get a fix into mm/gup.c,
> but if some other kernel path tries calling set_page_dirty() on a
> file-backed page without first asking permission from the file system,
> it seems to be nice if the file system doesn't BUG() --- as near as I
> can tell, xfs isn't crashing in this case, but ext4 is.
iomap is probably refusing to map holes for writepage - we've
cleaned up most of the weird edge cases to return errors, so I'm
guessing iomap is just ignoring such pages these days.
Yeah, see iomap_writepage_map():
error = wpc->ops->map_blocks(wpc, inode, pos);
if (error)
break;
if (WARN_ON_ONCE(wpc->iomap.type == IOMAP_INLINE))
continue;
if (wpc->iomap.type == IOMAP_HOLE)
continue;
Yeah, so if writeback maps a hole rather than converts a delalloc
region to IOMAP_MAPPED, it'll just skip over the block/page. IIRC,
they essentially become uncleanable pages, and I think eventually
inode reclaim will just toss them out of memory.
Cheers,
Dave.
--
Dave Chinner
[email protected]