Re: [PATCH] udf: Fix a slab-out-of-bounds write bug in udf_find_entry()

[Jan Kara <jack@suse.cz>]

On Wed 09-11-22 01:35:42, Peng Zhang wrote:
> From: ZhangPeng <zhangpeng362@huawei.com>
> 
> Syzbot reported a slab-out-of-bounds Write bug:
> 
> loop0: detected capacity change from 0 to 2048
> ==================================================================
> BUG: KASAN: slab-out-of-bounds in udf_find_entry+0x8a5/0x14f0
> fs/udf/namei.c:253
> Write of size 105 at addr ffff8880123ff896 by task syz-executor323/3610
> 
> CPU: 0 PID: 3610 Comm: syz-executor323 Not tainted
> 6.1.0-rc2-syzkaller-00105-gb229b6ca5abb #0
> Hardware name: Google Compute Engine/Google Compute Engine, BIOS
> Google 10/11/2022
> Call Trace:
>  <TASK>
>  __dump_stack lib/dump_stack.c:88 [inline]
>  dump_stack_lvl+0x1b1/0x28e lib/dump_stack.c:106
>  print_address_description+0x74/0x340 mm/kasan/report.c:284
>  print_report+0x107/0x1f0 mm/kasan/report.c:395
>  kasan_report+0xcd/0x100 mm/kasan/report.c:495
>  kasan_check_range+0x2a7/0x2e0 mm/kasan/generic.c:189
>  memcpy+0x3c/0x60 mm/kasan/shadow.c:66
>  udf_find_entry+0x8a5/0x14f0 fs/udf/namei.c:253
>  udf_lookup+0xef/0x340 fs/udf/namei.c:309
>  lookup_open fs/namei.c:3391 [inline]
>  open_last_lookups fs/namei.c:3481 [inline]
>  path_openat+0x10e6/0x2df0 fs/namei.c:3710
>  do_filp_open+0x264/0x4f0 fs/namei.c:3740
>  do_sys_openat2+0x124/0x4e0 fs/open.c:1310
>  do_sys_open fs/open.c:1326 [inline]
>  __do_sys_creat fs/open.c:1402 [inline]
>  __se_sys_creat fs/open.c:1396 [inline]
>  __x64_sys_creat+0x11f/0x160 fs/open.c:1396
>  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>  do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80
>  entry_SYSCALL_64_after_hwframe+0x63/0xcd
> RIP: 0033:0x7ffab0d164d9
> Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 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 c0 ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007ffe1a7e6bb8 EFLAGS: 00000246 ORIG_RAX: 0000000000000055
> RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007ffab0d164d9
> RDX: 00007ffab0d164d9 RSI: 0000000000000000 RDI: 0000000020000180
> RBP: 00007ffab0cd5a10 R08: 0000000000000000 R09: 0000000000000000
> R10: 00005555573552c0 R11: 0000000000000246 R12: 00007ffab0cd5aa0
> R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
>  </TASK>
> 
> Allocated by task 3610:
>  kasan_save_stack mm/kasan/common.c:45 [inline]
>  kasan_set_track+0x3d/0x60 mm/kasan/common.c:52
>  ____kasan_kmalloc mm/kasan/common.c:371 [inline]
>  __kasan_kmalloc+0x97/0xb0 mm/kasan/common.c:380
>  kmalloc include/linux/slab.h:576 [inline]
>  udf_find_entry+0x7b6/0x14f0 fs/udf/namei.c:243
>  udf_lookup+0xef/0x340 fs/udf/namei.c:309
>  lookup_open fs/namei.c:3391 [inline]
>  open_last_lookups fs/namei.c:3481 [inline]
>  path_openat+0x10e6/0x2df0 fs/namei.c:3710
>  do_filp_open+0x264/0x4f0 fs/namei.c:3740
>  do_sys_openat2+0x124/0x4e0 fs/open.c:1310
>  do_sys_open fs/open.c:1326 [inline]
>  __do_sys_creat fs/open.c:1402 [inline]
>  __se_sys_creat fs/open.c:1396 [inline]
>  __x64_sys_creat+0x11f/0x160 fs/open.c:1396
>  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>  do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80
>  entry_SYSCALL_64_after_hwframe+0x63/0xcd
> 
> The buggy address belongs to the object at ffff8880123ff800
>  which belongs to the cache kmalloc-256 of size 256
> The buggy address is located 150 bytes inside of
>  256-byte region [ffff8880123ff800, ffff8880123ff900)
> 
> The buggy address belongs to the physical page:
> page:ffffea000048ff80 refcount:1 mapcount:0 mapping:0000000000000000
> index:0x0 pfn:0x123fe
> head:ffffea000048ff80 order:1 compound_mapcount:0 compound_pincount:0
> flags: 0xfff00000010200(slab|head|node=0|zone=1|lastcpupid=0x7ff)
> raw: 00fff00000010200 ffffea00004b8500 dead000000000003 ffff888012041b40
> raw: 0000000000000000 0000000080100010 00000001ffffffff 0000000000000000
> page dumped because: kasan: bad access detected
> page_owner tracks the page as allocated
> page last allocated via order 0, migratetype Unmovable, gfp_mask 0x0(),
> pid 1, tgid 1 (swapper/0), ts 1841222404, free_ts 0
>  create_dummy_stack mm/page_owner.c:67 [inline]
>  register_early_stack+0x77/0xd0 mm/page_owner.c:83
>  init_page_owner+0x3a/0x731 mm/page_owner.c:93
>  kernel_init_freeable+0x41c/0x5d5 init/main.c:1629
>  kernel_init+0x19/0x2b0 init/main.c:1519
> page_owner free stack trace missing
> 
> Memory state around the buggy address:
>  ffff8880123ff780: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>  ffff8880123ff800: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> >ffff8880123ff880: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 06
>                                                                 ^
>  ffff8880123ff900: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>  ffff8880123ff980: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> ==================================================================
> 
> Fix this by changing the memory size allocated for copy_name from
> UDF_NAME_LEN(254) to UDF_NAME_LEN_CS0(255), because the total length
> (lfi) of subsequent memcpy can be up to 255.
> 
> Reported-by: syzbot+69c9fdccc6dd08961d34@syzkaller.appspotmail.com
> Fixes: 066b9cded00b ("udf: Use separate buffer for copying split names")
> Signed-off-by: ZhangPeng <zhangpeng362@huawei.com>

Ah, good catch! Thanks for the fix! I've added it to my tree and will push
it to Linus tomorrow.

								Honza


> ---
>  fs/udf/namei.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/udf/namei.c b/fs/udf/namei.c
> index fb4c30e05245..ae7bc13a5298 100644
> --- a/fs/udf/namei.c
> +++ b/fs/udf/namei.c
> @@ -240,7 +240,7 @@ static struct fileIdentDesc *udf_find_entry(struct inode *dir,
>  						      poffset - lfi);
>  			else {
>  				if (!copy_name) {
> -					copy_name = kmalloc(UDF_NAME_LEN,
> +					copy_name = kmalloc(UDF_NAME_LEN_CS0,
>  							    GFP_NOFS);
>  					if (!copy_name) {
>  						fi = ERR_PTR(-ENOMEM);
> -- 
> 2.25.1
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR