Message-ID: <20190627110654.GA13946@infradead.org>
Date:   Thu, 27 Jun 2019 04:06:54 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     syzbot <syzbot+b75afdbe271a0d7ac4f6@...kaller.appspotmail.com>
Cc:     darrick.wong@...cle.com, linux-kernel@...r.kernel.org,
        linux-xfs@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: Re: KASAN: use-after-free Read in xlog_alloc_log

It seems like this is the xlog_alloc_log error path.  We didn't
really change anything in the circular ioclogs queue handling, so
maybe thish has been there before, but xfs_buf wasn't wired up to
kasan to catch it?

Either way I suspect the right thing to do is to replace the list
with an array based lookup.  I'll look into that, maybe a reproducer
appears until then.

On Wed, Jun 26, 2019 at 11:50:06PM -0700, syzbot wrote:
> Hello,
> 
> syzbot found the following crash on:
> 
> HEAD commit:    1dd45f17 Add linux-next specific files for 20190626
> git tree:       linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=172479e9a00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=c1222640552e42a5
> dashboard link: https://syzkaller.appspot.com/bug?extid=b75afdbe271a0d7ac4f6
> compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
> 
> Unfortunately, I don't have any reproducer for this crash yet.
> 
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+b75afdbe271a0d7ac4f6@...kaller.appspotmail.com
> 
> XFS (loop5): Mounting V4 Filesystem
> ==================================================================
> BUG: KASAN: use-after-free in xlog_alloc_log+0x1266/0x1380
> fs/xfs/xfs_log.c:1478
> Read of size 8 at addr ffff8880693e2990 by task syz-executor.5/12241
> 
> CPU: 1 PID: 12241 Comm: syz-executor.5 Not tainted 5.2.0-rc6-next-20190626
> #23
> 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+0x172/0x1f0 lib/dump_stack.c:113
>  print_address_description.cold+0xd4/0x306 mm/kasan/report.c:351
>  __kasan_report.cold+0x1b/0x36 mm/kasan/report.c:482
>  kasan_report+0x12/0x17 mm/kasan/common.c:614
>  __asan_report_load8_noabort+0x14/0x20 mm/kasan/generic_report.c:132
>  xlog_alloc_log+0x1266/0x1380 fs/xfs/xfs_log.c:1478
>  xfs_log_mount+0xdc/0x780 fs/xfs/xfs_log.c:580
>  xfs_mountfs+0xdb9/0x1be0 fs/xfs/xfs_mount.c:815
>  xfs_fs_fill_super+0xca6/0x16c0 fs/xfs/xfs_super.c:1740
>  mount_bdev+0x304/0x3c0 fs/super.c:1346
>  xfs_fs_mount+0x35/0x40 fs/xfs/xfs_super.c:1814
>  legacy_get_tree+0x108/0x220 fs/fs_context.c:661
>  vfs_get_tree+0x8e/0x390 fs/super.c:1476
>  do_new_mount fs/namespace.c:2791 [inline]
>  do_mount+0x138c/0x1c00 fs/namespace.c:3111
>  ksys_mount+0xdb/0x150 fs/namespace.c:3320
>  __do_sys_mount fs/namespace.c:3334 [inline]
>  __se_sys_mount fs/namespace.c:3331 [inline]
>  __x64_sys_mount+0xbe/0x150 fs/namespace.c:3331
>  do_syscall_64+0xfd/0x6a0 arch/x86/entry/common.c:301
>  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> RIP: 0033:0x45bf6a
> Code: b8 a6 00 00 00 0f 05 48 3d 01 f0 ff ff 0f 83 9d 8d fb ff c3 66 2e 0f
> 1f 84 00 00 00 00 00 66 90 49 89 ca b8 a5 00 00 00 0f 05 <48> 3d 01 f0 ff ff
> 0f 83 7a 8d fb ff c3 66 0f 1f 84 00 00 00 00 00
> RSP: 002b:00007fac99605a88 EFLAGS: 00000206 ORIG_RAX: 00000000000000a5
> RAX: ffffffffffffffda RBX: 00007fac99605b40 RCX: 000000000045bf6a
> RDX: 00007fac99605ae0 RSI: 0000000020000000 RDI: 00007fac99605b00
> RBP: 0000000000000001 R08: 00007fac99605b40 R09: 00007fac99605ae0
> R10: 0000000000000000 R11: 0000000000000206 R12: 0000000000000004
> R13: 00000000004c858e R14: 00000000004df0e0 R15: 00000000ffffffff
> 
> Allocated by task 12241:
>  save_stack+0x23/0x90 mm/kasan/common.c:71
>  set_track mm/kasan/common.c:79 [inline]
>  __kasan_kmalloc mm/kasan/common.c:489 [inline]
>  __kasan_kmalloc.constprop.0+0xcf/0xe0 mm/kasan/common.c:462
>  kasan_kmalloc+0x9/0x10 mm/kasan/common.c:503
>  __do_kmalloc mm/slab.c:3656 [inline]
>  __kmalloc+0x163/0x770 mm/slab.c:3665
>  kmalloc include/linux/slab.h:556 [inline]
>  kmem_alloc+0xd2/0x200 fs/xfs/kmem.c:24
>  kmem_zalloc fs/xfs/kmem.h:73 [inline]
>  xlog_alloc_log+0xbf4/0x1380 fs/xfs/xfs_log.c:1420
>  xfs_log_mount+0xdc/0x780 fs/xfs/xfs_log.c:580
>  xfs_mountfs+0xdb9/0x1be0 fs/xfs/xfs_mount.c:815
>  xfs_fs_fill_super+0xca6/0x16c0 fs/xfs/xfs_super.c:1740
>  mount_bdev+0x304/0x3c0 fs/super.c:1346
>  xfs_fs_mount+0x35/0x40 fs/xfs/xfs_super.c:1814
>  legacy_get_tree+0x108/0x220 fs/fs_context.c:661
>  vfs_get_tree+0x8e/0x390 fs/super.c:1476
>  do_new_mount fs/namespace.c:2791 [inline]
>  do_mount+0x138c/0x1c00 fs/namespace.c:3111
>  ksys_mount+0xdb/0x150 fs/namespace.c:3320
>  __do_sys_mount fs/namespace.c:3334 [inline]
>  __se_sys_mount fs/namespace.c:3331 [inline]
>  __x64_sys_mount+0xbe/0x150 fs/namespace.c:3331
>  do_syscall_64+0xfd/0x6a0 arch/x86/entry/common.c:301
>  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> 
> Freed by task 12241:
>  save_stack+0x23/0x90 mm/kasan/common.c:71
>  set_track mm/kasan/common.c:79 [inline]
>  __kasan_slab_free+0x102/0x150 mm/kasan/common.c:451
>  kasan_slab_free+0xe/0x10 mm/kasan/common.c:459
>  __cache_free mm/slab.c:3426 [inline]
>  kfree+0x10a/0x2c0 mm/slab.c:3757
>  kvfree+0x61/0x70 mm/util.c:488
>  kmem_free fs/xfs/kmem.h:66 [inline]
>  xlog_alloc_log+0xea9/0x1380 fs/xfs/xfs_log.c:1480
>  xfs_log_mount+0xdc/0x780 fs/xfs/xfs_log.c:580
>  xfs_mountfs+0xdb9/0x1be0 fs/xfs/xfs_mount.c:815
>  xfs_fs_fill_super+0xca6/0x16c0 fs/xfs/xfs_super.c:1740
>  mount_bdev+0x304/0x3c0 fs/super.c:1346
>  xfs_fs_mount+0x35/0x40 fs/xfs/xfs_super.c:1814
>  legacy_get_tree+0x108/0x220 fs/fs_context.c:661
>  vfs_get_tree+0x8e/0x390 fs/super.c:1476
>  do_new_mount fs/namespace.c:2791 [inline]
>  do_mount+0x138c/0x1c00 fs/namespace.c:3111
>  ksys_mount+0xdb/0x150 fs/namespace.c:3320
>  __do_sys_mount fs/namespace.c:3334 [inline]
>  __se_sys_mount fs/namespace.c:3331 [inline]
>  __x64_sys_mount+0xbe/0x150 fs/namespace.c:3331
>  do_syscall_64+0xfd/0x6a0 arch/x86/entry/common.c:301
>  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> 
> The buggy address belongs to the object at ffff8880693e2900
>  which belongs to the cache kmalloc-1k of size 1024
> The buggy address is located 144 bytes inside of
>  1024-byte region [ffff8880693e2900, ffff8880693e2d00)
> The buggy address belongs to the page:
> page:ffffea0001a4f880 refcount:1 mapcount:0 mapping:ffff8880aa400c40
> index:0x0 compound_mapcount: 0
> flags: 0x1fffc0000010200(slab|head)
> raw: 01fffc0000010200 ffffea00018ec788 ffffea0002473908 ffff8880aa400c40
> raw: 0000000000000000 ffff8880693e2000 0000000100000007 0000000000000000
> page dumped because: kasan: bad access detected
> 
> Memory state around the buggy address:
>  ffff8880693e2880: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>  ffff8880693e2900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> > ffff8880693e2980: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>                          ^
>  ffff8880693e2a00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>  ffff8880693e2a80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ==================================================================
> 
> 
> ---
> This bug 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@...glegroups.com.
> 
> syzbot will keep track of this bug report. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
---end quoted text---

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