The patch titled
Subject: mm: shmem: fix data-race in shmem_getattr()
has been added to the -mm mm-unstable branch. Its filename is
mm-shmem-fix-data-race-in-shmem_getattr.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-shmem-fix-data-race-in-shmem_getattr.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Jeongjun Park <aha310510@xxxxxxxxx>
Subject: mm: shmem: fix data-race in shmem_getattr()
Date: Mon, 9 Sep 2024 21:35:58 +0900
I got the following KCSAN report during syzbot testing:
==================================================================
BUG: KCSAN: data-race in generic_fillattr / inode_set_ctime_current
write to 0xffff888102eb3260 of 4 bytes by task 6565 on cpu 1:
inode_set_ctime_to_ts include/linux/fs.h:1638 [inline]
inode_set_ctime_current+0x169/0x1d0 fs/inode.c:2626
shmem_mknod+0x117/0x180 mm/shmem.c:3443
shmem_create+0x34/0x40 mm/shmem.c:3497
lookup_open fs/namei.c:3578 [inline]
open_last_lookups fs/namei.c:3647 [inline]
path_openat+0xdbc/0x1f00 fs/namei.c:3883
do_filp_open+0xf7/0x200 fs/namei.c:3913
do_sys_openat2+0xab/0x120 fs/open.c:1416
do_sys_open fs/open.c:1431 [inline]
__do_sys_openat fs/open.c:1447 [inline]
__se_sys_openat fs/open.c:1442 [inline]
__x64_sys_openat+0xf3/0x120 fs/open.c:1442
x64_sys_call+0x1025/0x2d60 arch/x86/include/generated/asm/syscalls_64.h:258
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0x54/0x120 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x76/0x7e
read to 0xffff888102eb3260 of 4 bytes by task 3498 on cpu 0:
inode_get_ctime_nsec include/linux/fs.h:1623 [inline]
inode_get_ctime include/linux/fs.h:1629 [inline]
generic_fillattr+0x1dd/0x2f0 fs/stat.c:62
shmem_getattr+0x17b/0x200 mm/shmem.c:1157
vfs_getattr_nosec fs/stat.c:166 [inline]
vfs_getattr+0x19b/0x1e0 fs/stat.c:207
vfs_statx_path fs/stat.c:251 [inline]
vfs_statx+0x134/0x2f0 fs/stat.c:315
vfs_fstatat+0xec/0x110 fs/stat.c:341
__do_sys_newfstatat fs/stat.c:505 [inline]
__se_sys_newfstatat+0x58/0x260 fs/stat.c:499
__x64_sys_newfstatat+0x55/0x70 fs/stat.c:499
x64_sys_call+0x141f/0x2d60 arch/x86/include/generated/asm/syscalls_64.h:263
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0x54/0x120 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x76/0x7e
value changed: 0x2755ae53 -> 0x27ee44d3
Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 3498 Comm: udevd Not tainted 6.11.0-rc6-syzkaller-00326-gd1f2d51b711a-dirty #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/06/2024
==================================================================
Since there is no special protection when shmem_getattr() calls
generic_fillattr(), data-race occurs by functions such as shmem_unlink()
or shmem_mknod(). This can cause unexpected results, so commenting it out
is not enough.
Therefore, when calling generic_fillattr() from shmem_getattr(), it is
appropriate to protect the inode using inode_lock_shared() and
inode_unlock_shared() to prevent data-race.
Link: https://lkml.kernel.org/r/20240909123558.70229-1-aha310510@xxxxxxxxx
Fixes: 44a30220bc0a ("shmem: recalculate file inode when fstat")
Signed-off-by: Jeongjun Park <aha310510@xxxxxxxxx>
Reported-by: syzbot <syzkaller@xxxxxxxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Yu Zhao <yuzhao@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/shmem.c | 2 ++
1 file changed, 2 insertions(+)
--- a/mm/shmem.c~mm-shmem-fix-data-race-in-shmem_getattr
+++ a/mm/shmem.c
@@ -1166,7 +1166,9 @@ static int shmem_getattr(struct mnt_idma
stat->attributes_mask |= (STATX_ATTR_APPEND |
STATX_ATTR_IMMUTABLE |
STATX_ATTR_NODUMP);
+ inode_lock_shared(inode);
generic_fillattr(idmap, request_mask, inode, stat);
+ inode_unlock_shared(inode);
if (shmem_huge_global_enabled(inode, 0, 0, false, NULL, 0))
stat->blksize = HPAGE_PMD_SIZE;
_
Patches currently in -mm which might be from aha310510@xxxxxxxxx are
mm-migrate-annotate-data-race-in-migrate_folio_unmap.patch
mm-percpu-fix-typo-to-pcpu_alloc_noprof-description.patch
mm-shmem-fix-data-race-in-shmem_getattr.patch
