CVE-2022-50432

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

kernfs: fix use-after-free in __kernfs_remove

Syzkaller managed to trigger concurrent calls to

kernfs_remove_by_name_ns() for the same file resulting in

a KASAN detected use-after-free. The race occurs when the root

node is freed during kernfs_drain().

To prevent this acquire an additional reference for the root

of the tree that is removed before calling __kernfs_remove().

Found by syzkaller with the following reproducer (slab_nomerge is

required):

syz_mount_image$ext4(0x0, &(0x7f0000000100)='./file0\x00', 0x100000, 0x0, 0x0, 0x0, 0x0)

r0 = openat(0xffffffffffffff9c, &(0x7f0000000080)='/proc/self/exe\x00', 0x0, 0x0)

close(r0)

pipe2(&(0x7f0000000140)={0xffffffffffffffff, <r1=>0xffffffffffffffff}, 0x800)

mount$9p_fd(0x0, &(0x7f0000000040)='./file0\x00', &(0x7f00000000c0), 0x408, &(0x7f0000000280)={'trans=fd,', {'rfdno', 0x3d, r0}, 0x2c, {'wfdno', 0x3d, r1}, 0x2c, {[{@cache_loose}, {@mmap}, {@loose}, {@loose}, {@mmap}], [{@mask={'mask', 0x3d, '^MAY_EXEC'}}, {@fsmagic={'fsmagic', 0x3d, 0x10001}}, {@dont_hash}]}})

Sample report:

==================================================================

BUG: KASAN: use-after-free in kernfs_type include/linux/kernfs.h:335 [inline]

BUG: KASAN: use-after-free in kernfs_leftmost_descendant fs/kernfs/dir.c:1261 [inline]

BUG: KASAN: use-after-free in __kernfs_remove.part.0+0x843/0x960 fs/kernfs/dir.c:1369

Read of size 2 at addr ffff8880088807f0 by task syz-executor.2/857

CPU: 0 PID: 857 Comm: syz-executor.2 Not tainted 6.0.0-rc3-00363-g7726d4c3e60b #5

Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014

Call Trace:

<TASK>

__dump_stack lib/dump_stack.c:88 [inline]

dump_stack_lvl+0x6e/0x91 lib/dump_stack.c:106

print_address_description mm/kasan/report.c:317 [inline]

print_report.cold+0x5e/0x5e5 mm/kasan/report.c:433

kasan_report+0xa3/0x130 mm/kasan/report.c:495

kernfs_type include/linux/kernfs.h:335 [inline]

kernfs_leftmost_descendant fs/kernfs/dir.c:1261 [inline]

__kernfs_remove.part.0+0x843/0x960 fs/kernfs/dir.c:1369

__kernfs_remove fs/kernfs/dir.c:1356 [inline]

kernfs_remove_by_name_ns+0x108/0x190 fs/kernfs/dir.c:1589

sysfs_slab_add+0x133/0x1e0 mm/slub.c:5943

__kmem_cache_create+0x3e0/0x550 mm/slub.c:4899

create_cache mm/slab_common.c:229 [inline]

kmem_cache_create_usercopy+0x167/0x2a0 mm/slab_common.c:335

p9_client_create+0xd4d/0x1190 net/9p/client.c:993

v9fs_session_init+0x1e6/0x13c0 fs/9p/v9fs.c:408

v9fs_mount+0xb9/0xbd0 fs/9p/vfs_super.c:126

legacy_get_tree+0xf1/0x200 fs/fs_context.c:610

vfs_get_tree+0x85/0x2e0 fs/super.c:1530

do_new_mount fs/namespace.c:3040 [inline]

path_mount+0x675/0x1d00 fs/namespace.c:3370

do_mount fs/namespace.c:3383 [inline]

__do_sys_mount fs/namespace.c:3591 [inline]

__se_sys_mount fs/namespace.c:3568 [inline]

__x64_sys_mount+0x282/0x300 fs/namespace.c:3568

do_syscall_x64 arch/x86/entry/common.c:50 [inline]

do_syscall_64+0x38/0x90 arch/x86/entry/common.c:80

entry_SYSCALL_64_after_hwframe+0x63/0xcd

RIP: 0033:0x7f725f983aed

Code: 02 b8 ff ff ff ff c3 66 0f 1f 44 00 00 f3 0f 1e fa 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 b0 ff ff ff f7 d8 64 89 01 48

RSP: 002b:00007f725f0f7028 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5

RAX: ffffffffffffffda RBX: 00007f725faa3f80 RCX: 00007f725f983aed

RDX: 00000000200000c0 RSI: 0000000020000040 RDI: 0000000000000000

RBP: 00007f725f9f419c R08: 0000000020000280 R09: 0000000000000000

R10: 0000000000000408 R11: 0000000000000246 R12: 0000000000000000

R13: 0000000000000006 R14: 00007f725faa3f80 R15: 00007f725f0d7000

</TASK>

Allocated by task 855:

kasan_save_stack+0x1e/0x40 mm/kasan/common.c:38

kasan_set_track mm/kasan/common.c:45 [inline]

set_alloc_info mm/kasan/common.c:437 [inline]

__kasan_slab_alloc+0x66/0x80 mm/kasan/common.c:470

kasan_slab_alloc include/linux/kasan.h:224 [inline]

slab_post_alloc_hook mm/slab.h:7

---truncated---