Re: KASAN: slab-out-of-bounds Read in squashfs_export_iget

[Marco Elver]

On Thu, 10 Dec 2020 at 11:43, syzbot
<syzbot+04419e3ff19d2970ea28@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
>
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit:    a9e26cb5 Add linux-next specific files for 20201208
> git tree:       linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=1674f80f500000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=e259434a8eaf0206
> dashboard link: https://syzkaller.appspot.com/bug?extid=04419e3ff19d2970ea28
> compiler:       gcc (GCC) 10.1.0-syz 20200507
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=136a6adf500000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=10457ccb500000
>
> The issue was bisected to:
>
> commit 555f63cd88404e122e8d31d0f925e430bd3f32d9
> Author: Alexander Potapenko <glider@xxxxxxxxxx>
> Date:   Fri Dec 4 03:19:29 2020 +0000
>
>     mm, kfence: insert KFENCE hooks for SLUB

This appears to be flaky bisection, and is not due to KFENCE.

It can be reproduced even with CONFIG_KFENCE=n, and also reverting
"mm, kfence: insert KFENCE hooks for SLUB" entirely.

Thanks,
-- Marco

> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=1619bb7f500000
> final oops:     https://syzkaller.appspot.com/x/report.txt?x=1519bb7f500000
> console output: https://syzkaller.appspot.com/x/log.txt?x=1119bb7f500000
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+04419e3ff19d2970ea28@xxxxxxxxxxxxxxxxxxxxxxxxx
> Fixes: 555f63cd8840 ("mm, kfence: insert KFENCE hooks for SLUB")
>
> loop0: detected capacity change from 264192 to 0
> ==================================================================
> BUG: KASAN: slab-out-of-bounds in squashfs_inode_lookup fs/squashfs/export.c:44 [inline]
> BUG: KASAN: slab-out-of-bounds in squashfs_export_iget+0x274/0x2a0 fs/squashfs/export.c:69
> Read of size 8 at addr ffff88801c6f6e08 by task syz-executor839/8488
>
> CPU: 0 PID: 8488 Comm: syz-executor839 Not tainted 5.10.0-rc7-next-20201208-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Call Trace:
>  __dump_stack lib/dump_stack.c:79 [inline]
>  dump_stack+0x107/0x163 lib/dump_stack.c:120
>  print_address_description.constprop.0.cold+0x5b/0x2f8 mm/kasan/report.c:230
>  __kasan_report mm/kasan/report.c:396 [inline]
>  kasan_report.cold+0x79/0xd5 mm/kasan/report.c:413
>  squashfs_inode_lookup fs/squashfs/export.c:44 [inline]
>  squashfs_export_iget+0x274/0x2a0 fs/squashfs/export.c:69
>  squashfs_fh_to_dentry fs/squashfs/export.c:84 [inline]
>  squashfs_fh_to_dentry+0x78/0xb0 fs/squashfs/export.c:77
>  exportfs_decode_fh_raw+0x127/0x7a0 fs/exportfs/expfs.c:436
>  exportfs_decode_fh+0x38/0x90 fs/exportfs/expfs.c:575
>  do_handle_to_path fs/fhandle.c:152 [inline]
>  handle_to_path fs/fhandle.c:207 [inline]
>  do_handle_open+0x2b6/0x7f0 fs/fhandle.c:223
>  do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
>  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> RIP: 0033:0x4443d9
> Code: 8d d7 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 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 5b d7 fb ff c3 66 2e 0f 1f 84 00 00 00 00
> RSP: 002b:00007ffd937fcd78 EFLAGS: 00000246 ORIG_RAX: 0000000000000130
> RAX: ffffffffffffffda RBX: 00000000004002e0 RCX: 00000000004443d9
> RDX: 0000000000000000 RSI: 0000000020000280 RDI: 0000000000000005
> RBP: 00000000006cf018 R08: 00007ffd00000015 R09: 00000000004002e0
> R10: 00007ffd937fcc20 R11: 0000000000000246 R12: 0000000000401fc0
> R13: 0000000000402050 R14: 0000000000000000 R15: 0000000000000000
>
> Allocated by task 6500:
>  kasan_save_stack+0x1b/0x40 mm/kasan/common.c:39
>  kasan_set_track mm/kasan/common.c:47 [inline]
>  set_alloc_info mm/kasan/common.c:405 [inline]
>  ____kasan_kmalloc mm/kasan/common.c:436 [inline]
>  ____kasan_kmalloc.constprop.0+0xa0/0xd0 mm/kasan/common.c:408
>  kmalloc include/linux/slab.h:570 [inline]
>  kzalloc include/linux/slab.h:695 [inline]
>  lsm_cred_alloc security/security.c:534 [inline]
>  security_prepare_creds+0x10e/0x190 security/security.c:1633
>  prepare_creds+0x509/0x730 kernel/cred.c:285
>  access_override_creds fs/open.c:353 [inline]
>  do_faccessat+0x3d7/0x870 fs/open.c:417
>  do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
>  entry_SYSCALL_64_after_hwframe+0x44/0xa9
>
> The buggy address belongs to the object at ffff88801c6f6de8
>  which belongs to the cache kmalloc-8 of size 8
> The buggy address is located 24 bytes to the right of
>  8-byte region [ffff88801c6f6de8, ffff88801c6f6df0)
> The buggy address belongs to the page:
> page:0000000061a643f0 refcount:1 mapcount:0 mapping:0000000000000000 index:0xffff88801c6f6de8 pfn:0x1c6f6
> flags: 0xfff00000000200(slab)
> raw: 00fff00000000200 ffffea0000625500 0000000500000005 ffff888010841c80
> raw: ffff88801c6f6de8 000000008066005d 00000001ffffffff 0000000000000000
> page dumped because: kasan: bad access detected
>
> Memory state around the buggy address:
>  ffff88801c6f6d00: fc fc fc fc fb fc fc fc fc fb fc fc fc fc fb fc
>  ffff88801c6f6d80: fc fc fc fb fc fc fc fc fa fc fc fc fc fb fc fc
> >ffff88801c6f6e00: fc fc 00 fc fc fc fc fa fc fc fc fc fb fc fc fc
>                       ^
>  ffff88801c6f6e80: fc 00 fc fc fc fc fa fc fc fc fc fb fc fc fc fc
>  ffff88801c6f6f00: 00 fc fc fc fc fa fc fc fc fc fb fc fc fc fc fb
> ==================================================================
>
>
> ---
> This report is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@xxxxxxxxxxxxxxxx.
>
> syzbot will keep track of this issue. See:
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> For information about bisection process see: https://goo.gl/tpsmEJ#bisection
> syzbot can test patches for this issue, for details see:
> https://goo.gl/tpsmEJ#testing-patches