Note: Versions mentioned in the description apply only to the upstream kernel-debug package and not the kernel-debug package as distributed by RHEL. See How to fix? for RHEL:7 relevant fixed versions and status.

In the Linux kernel, the following vulnerability has been resolved:

mm: shmem: fix data-race in shmem_getattr()

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

When calling generic_fillattr(), if you don't hold read lock, data-race will occur in inode member variables, which can cause unexpected behavior.

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.

• https://access.redhat.com/security/cve/CVE-2024-50228
• https://git.kernel.org/stable/c/3d9528484480e8f4979b3a347930ed383be99f89
• https://git.kernel.org/stable/c/7cc30ada84323be19395094d567579536e0d187e
• https://git.kernel.org/stable/c/82cae1e30bd940253593c2d4f16d88343d1358f4
• https://git.kernel.org/stable/c/9fb9703cd43ee20a6de8ccdef991677b7274cec0
• https://git.kernel.org/stable/c/bda1a99a0dd644f31a87d636ac624eeb975cb65a
• https://git.kernel.org/stable/c/d949d1d14fa281ace388b1de978e8f2cd52875cf
• https://git.kernel.org/stable/c/edd1f905050686fdc4cfe233d818469fdf7d5ff8
• https://git.kernel.org/stable/c/ffd56612566bc23877c8f45def2801f3324a222a