KASAN: slab-out-of-bounds Read in vsscanf

Fri Mar 27 01:20:14 UTC 2020

Hello,

syzbot found the following crash on:

HEAD commit:    1b649e0b Merge git://git.kernel.org/pub/scm/linux/kernel/g..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=11044405e00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=4ac76c43beddbd9
dashboard link: https://syzkaller.appspot.com/bug?extid=bfdd4a2f07be52351350
compiler:       clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=13819303e00000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=13eaed4be00000

Bisection is inconclusive: the bug happens on the oldest tested release.

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=150e6ac5e00000
final crash:    https://syzkaller.appspot.com/x/report.txt?x=170e6ac5e00000
console output: https://syzkaller.appspot.com/x/log.txt?x=130e6ac5e00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+bfdd4a2f07be52351350 at syzkaller.appspotmail.com

==================================================================
BUG: KASAN: slab-out-of-bounds in vsscanf+0x2666/0x2ef0 lib/vsprintf.c:3275
Read of size 1 at addr ffff888093622f42 by task syz-executor055/7117

CPU: 1 PID: 7117 Comm: syz-executor055 Not tainted 5.6.0-rc7-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x1e9/0x30e lib/dump_stack.c:118
 print_address_description+0x74/0x5c0 mm/kasan/report.c:374
 __kasan_report+0x14b/0x1c0 mm/kasan/report.c:506
 kasan_report+0x25/0x50 mm/kasan/common.c:641
 vsscanf+0x2666/0x2ef0 lib/vsprintf.c:3275
 sscanf+0x6c/0x90 lib/vsprintf.c:3481
 smk_set_cipso+0x1ac/0x6a0 security/smack/smackfs.c:881
 __vfs_write+0xa7/0x710 fs/read_write.c:494
 vfs_write+0x271/0x570 fs/read_write.c:558
 ksys_write+0x115/0x220 fs/read_write.c:611
 do_syscall_64+0xf3/0x1b0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x4401b9
Code: 18 89 d0 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 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 0f 83 fb 13 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ffd20456888 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00000000004002c8 RCX: 00000000004401b9
RDX: 0000000000000001 RSI: 00000000200005c0 RDI: 0000000000000003
RBP: 00000000006ca018 R08: 00000000004002c8 R09: 00000000004002c8
R10: 00000000004002c8 R11: 0000000000000246 R12: 0000000000401a40
R13: 0000000000401ad0 R14: 0000000000000000 R15: 0000000000000000

Allocated by task 7117:
 save_stack mm/kasan/common.c:72 [inline]
 set_track mm/kasan/common.c:80 [inline]
 __kasan_kmalloc+0x118/0x1c0 mm/kasan/common.c:515
 __do_kmalloc mm/slab.c:3656 [inline]
 __kmalloc_track_caller+0x249/0x320 mm/slab.c:3671
 memdup_user_nul+0x26/0xf0 mm/util.c:259
 smk_set_cipso+0xff/0x6a0 security/smack/smackfs.c:859
 __vfs_write+0xa7/0x710 fs/read_write.c:494
 vfs_write+0x271/0x570 fs/read_write.c:558
 ksys_write+0x115/0x220 fs/read_write.c:611
 do_syscall_64+0xf3/0x1b0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 1:
 save_stack mm/kasan/common.c:72 [inline]
 set_track mm/kasan/common.c:80 [inline]
 kasan_set_free_info mm/kasan/common.c:337 [inline]
 __kasan_slab_free+0x12e/0x1e0 mm/kasan/common.c:476
 __cache_free mm/slab.c:3426 [inline]
 kfree+0x10a/0x220 mm/slab.c:3757
 tomoyo_path_perm+0x59b/0x740 security/tomoyo/file.c:842
 security_inode_getattr+0xc0/0x140 security/security.c:1254
 vfs_getattr+0x27/0x6e0 fs/stat.c:117
 vfs_statx fs/stat.c:201 [inline]
 vfs_lstat include/linux/fs.h:3277 [inline]
 __do_sys_newlstat fs/stat.c:364 [inline]
 __se_sys_newlstat+0x85/0x140 fs/stat.c:358
 do_syscall_64+0xf3/0x1b0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff888093622f40
 which belongs to the cache kmalloc-32 of size 32
The buggy address is located 2 bytes inside of
 32-byte region [ffff888093622f40, ffff888093622f60)
The buggy address belongs to the page:
page:ffffea00024d8880 refcount:1 mapcount:0 mapping:ffff8880aa4001c0 index:0xffff888093622fc1
flags: 0xfffe0000000200(slab)
raw: 00fffe0000000200 ffffea000271b988 ffffea00028ae488 ffff8880aa4001c0
raw: ffff888093622fc1 ffff888093622000 0000000100000039 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff888093622e00: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
 ffff888093622e80: fb fb fb fb fc fc fc fc 00 00 01 fc fc fc fc fc
>ffff888093622f00: fb fb fb fb fc fc fc fc 02 fc fc fc fc fc fc fc
                                           ^
 ffff888093622f80: fb fb fb fb fc fc fc fc fc fc fc fc fc fc fc fc
 ffff888093623000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
==================================================================

---
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