Re: KASAN: use-after-free Read in xlog_alloc_log (2)

Brian Foster
2019-12-03T13:48:52Z

On Fri, Nov 29, 2019 at 11:19:08PM -0800, syzbot wrote:
> Hello,
>
> syzbot found the following crash on:
>
> HEAD commit: 81b6b964 Merge branch 'master' of git://git.kernel.org/pub..
> git tree: upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=13b27696e00000
> kernel config: https://syzkaller.appspot.com/x/.config?x=773597fe8d7cb41a
> dashboard link: https://syzkaller.appspot.com/bug?extid=c732f8644185de340492
> compiler: gcc (GCC) 9.0.0 20181231 (experimental)
>
> Unfortunately, I don't have any reproducer for this crash yet.
>

It looks like the out_free_iclog: error path in xlog_alloc_log() doesn't
handle the case of a fully initialized iclog list. It uses an iclog !=
NULL check to terminate the freeing loop, and that might never occur if
we failed after the linked list was set up. I've confirmed with a simple
error injection test and will send a patch..

Brian

> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+c732f8644185de340492@syzkaller.appspotmail.com
>
> ==================================================================
> BUG: KASAN: use-after-free in xlog_alloc_log+0x1398/0x14b0
> fs/xfs/xfs_log.c:1495
> Read of size 8 at addr ffff888068139890 by task syz-executor.3/32544
>
> CPU: 0 PID: 32544 Comm: syz-executor.3 Not tainted 5.4.0-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+0x197/0x210 lib/dump_stack.c:118
> print_address_description.constprop.0.cold+0xd4/0x30b mm/kasan/report.c:374
> __kasan_report.cold+0x1b/0x41 mm/kasan/report.c:506
> kasan_report+0x12/0x20 mm/kasan/common.c:634
> __asan_report_load8_noabort+0x14/0x20 mm/kasan/generic_report.c:132
> xlog_alloc_log+0x1398/0x14b0 fs/xfs/xfs_log.c:1495
> xfs_log_mount+0xdc/0x780 fs/xfs/xfs_log.c:599
> xfs_mountfs+0xdb9/0x1be0 fs/xfs/xfs_mount.c:811
> xfs_fs_fill_super+0xd24/0x1750 fs/xfs/xfs_super.c:1732
> mount_bdev+0x304/0x3c0 fs/super.c:1415
> xfs_fs_mount+0x35/0x40 fs/xfs/xfs_super.c:1806
> legacy_get_tree+0x108/0x220 fs/fs_context.c:647
> vfs_get_tree+0x8e/0x300 fs/super.c:1545
> do_new_mount fs/namespace.c:2822 [inline]
> do_mount+0x135a/0x1b50 fs/namespace.c:3142
> ksys_mount+0xdb/0x150 fs/namespace.c:3351
> __do_sys_mount fs/namespace.c:3365 [inline]
> __se_sys_mount fs/namespace.c:3362 [inline]
> __x64_sys_mount+0xbe/0x150 fs/namespace.c:3362
> do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
> entry_SYSCALL_64_after_hwframe+0x49/0xbe
> RIP: 0033:0x45d0ca
> Code: b8 a6 00 00 00 0f 05 48 3d 01 f0 ff ff 0f 83 4d 8c 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 2a 8c fb ff c3 66 0f 1f 84 00 00 00 00 00
> RSP: 002b:00007f525b430a88 EFLAGS: 00000206 ORIG_RAX: 00000000000000a5
> RAX: ffffffffffffffda RBX: 00007f525b430b40 RCX: 000000000045d0ca
> RDX: 00007f525b430ae0 RSI: 0000000020000100 RDI: 00007f525b430b00
> RBP: 0000000000000001 R08: 00007f525b430b40 R09: 00007f525b430ae0
> R10: 0000000000000000 R11: 0000000000000206 R12: 0000000000000004
> R13: 00000000004ca258 R14: 00000000004e2870 R15: 00000000ffffffff
>
> Allocated by task 32544:
> save_stack+0x23/0x90 mm/kasan/common.c:69
> set_track mm/kasan/common.c:77 [inline]
> __kasan_kmalloc mm/kasan/common.c:510 [inline]
> __kasan_kmalloc.constprop.0+0xcf/0xe0 mm/kasan/common.c:483
> kasan_kmalloc+0x9/0x10 mm/kasan/common.c:524
> __do_kmalloc mm/slab.c:3655 [inline]
> __kmalloc+0x163/0x770 mm/slab.c:3664
> kmalloc include/linux/slab.h:561 [inline]
> kmem_alloc+0x15b/0x4d0 fs/xfs/kmem.c:21
> kmem_zalloc fs/xfs/kmem.h:68 [inline]
> xlog_alloc_log+0xcce/0x14b0 fs/xfs/xfs_log.c:1437
> xfs_log_mount+0xdc/0x780 fs/xfs/xfs_log.c:599
> xfs_mountfs+0xdb9/0x1be0 fs/xfs/xfs_mount.c:811
> xfs_fs_fill_super+0xd24/0x1750 fs/xfs/xfs_super.c:1732
> mount_bdev+0x304/0x3c0 fs/super.c:1415
> xfs_fs_mount+0x35/0x40 fs/xfs/xfs_super.c:1806
> legacy_get_tree+0x108/0x220 fs/fs_context.c:647
> vfs_get_tree+0x8e/0x300 fs/super.c:1545
> do_new_mount fs/namespace.c:2822 [inline]
> do_mount+0x135a/0x1b50 fs/namespace.c:3142
> ksys_mount+0xdb/0x150 fs/namespace.c:3351
> __do_sys_mount fs/namespace.c:3365 [inline]
> __se_sys_mount fs/namespace.c:3362 [inline]
> __x64_sys_mount+0xbe/0x150 fs/namespace.c:3362
> do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
> entry_SYSCALL_64_after_hwframe+0x49/0xbe
>
> Freed by task 32544:
> save_stack+0x23/0x90 mm/kasan/common.c:69
> set_track mm/kasan/common.c:77 [inline]
> kasan_set_free_info mm/kasan/common.c:332 [inline]
> __kasan_slab_free+0x102/0x150 mm/kasan/common.c:471
> kasan_slab_free+0xe/0x10 mm/kasan/common.c:480
> __cache_free mm/slab.c:3425 [inline]
> kfree+0x10a/0x2c0 mm/slab.c:3756
> kvfree+0x61/0x70 mm/util.c:593
> kmem_free fs/xfs/kmem.h:61 [inline]
> xlog_alloc_log+0xeb5/0x14b0 fs/xfs/xfs_log.c:1497
> xfs_log_mount+0xdc/0x780 fs/xfs/xfs_log.c:599
> xfs_mountfs+0xdb9/0x1be0 fs/xfs/xfs_mount.c:811
> xfs_fs_fill_super+0xd24/0x1750 fs/xfs/xfs_super.c:1732
> mount_bdev+0x304/0x3c0 fs/super.c:1415
> xfs_fs_mount+0x35/0x40 fs/xfs/xfs_super.c:1806
> legacy_get_tree+0x108/0x220 fs/fs_context.c:647
> vfs_get_tree+0x8e/0x300 fs/super.c:1545
> do_new_mount fs/namespace.c:2822 [inline]
> do_mount+0x135a/0x1b50 fs/namespace.c:3142
> ksys_mount+0xdb/0x150 fs/namespace.c:3351
> __do_sys_mount fs/namespace.c:3365 [inline]
> __se_sys_mount fs/namespace.c:3362 [inline]
> __x64_sys_mount+0xbe/0x150 fs/namespace.c:3362
> do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
> entry_SYSCALL_64_after_hwframe+0x49/0xbe
>
> The buggy address belongs to the object at ffff888068139800
> which belongs to the cache kmalloc-1k of size 1024
> The buggy address is located 144 bytes inside of
> 1024-byte region [ffff888068139800, ffff888068139c00)
> The buggy address belongs to the page:
> page:ffffea0001a04e40 refcount:1 mapcount:0 mapping:ffff8880aa400c40
> index:0x0
> raw: 00fffe0000000200 ffffea0002728148 ffffea00015604c8 ffff8880aa400c40
> raw: 0000000000000000 ffff888068139000 0000000100000002 0000000000000000
> page dumped because: kasan: bad access detected
>
> Memory state around the buggy address:
> ffff888068139780: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> ffff888068139800: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> > ffff888068139880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ^
> ffff888068139900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ffff888068139980: 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@googlegroups.com.
>
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>