Re: general protection fault in ext4_writepages

From: Ritesh Harjani
Date: Mon Nov 11 2019 - 00:12:51 EST

Hello Ted,

This issue seems to be coming via fault injection failure in slab
allocation. This should be fixed via below patch on your latest ext4
branch.

https://marc.info/?l=linux-ext4&m=804&w=2

Please let me know if anything else is needed.

-ritesh

On 11/11/19 5:14 AM, syzbot wrote:
Hello,

syzbot found the following crash on:

HEAD commit:ÂÂÂ dcd34bd2 Add linux-next specific files for 20191106
git tree:ÂÂÂÂÂÂ linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=11a0a4fce00000
kernel config:Â https://syzkaller.appspot.com/x/.config?x=742545dcdea21726
dashboard link: https://syzkaller.appspot.com/bug?extid=9567fda428fba259deba
compiler:ÂÂÂÂÂÂ gcc (GCC) 9.0.0 20181231 (experimental)
syz repro:ÂÂÂÂÂ https://syzkaller.appspot.com/x/repro.syz?x=1645c42ce00000
C reproducer:ÂÂ https://syzkaller.appspot.com/x/repro.c?x=1108a23ae00000

The bug was bisected to:

commit c8cc88163f40df39e50cda63ac361631864b453e
Author: Ritesh Harjani <riteshh@xxxxxxxxxxxxx>
Date:ÂÂ Wed Oct 16 07:37:10 2019 +0000

ÂÂÂ ext4: Add support for blocksize < pagesize in dioread_nolock

bisection log:Â https://syzkaller.appspot.com/x/bisect.txt?x=1044c6b4e00000
final crash:ÂÂÂ https://syzkaller.appspot.com/x/report.txt?x=1244c6b4e00000
console output: https://syzkaller.appspot.com/x/log.txt?x=1444c6b4e00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+9567fda428fba259deba@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: c8cc88163f40 ("ext4: Add support for blocksize < pagesize in dioread_nolock")

RDX: 0000000000000000 RSI: 0000000100000003 RDI: 0000000000000003
RBP: 0000000000000004 R08: 0000000000000001 R09: 00007fffd7a50033
R10: 0000000028120001 R11: 0000000000000246 R12: 0000000000401ef0
R13: 0000000000401f80 R14: 0000000000000000 R15: 0000000000000000
kasan: CONFIG_KASAN_INLINE enabled
kasan: GPF could be caused by NULL-ptr deref or user memory access
general protection fault: 0000 [#1] PREEMPT SMP KASAN
CPU: 0 PID: 8639 Comm: syz-executor031 Not tainted 5.4.0-rc6-next-20191106 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:mpage_map_and_submit_extent fs/ext4/inode.c:2557 [inline]
RIP: 0010:ext4_writepages+0x17b4/0x2e80 fs/ext4/inode.c:2911
Code: ff ff e8 1f cf b0 ff 48 8b 85 30 fe ff ff 48 8b 8d 00 fe ff ff 48 8d 78 10 48 89 fa 48 c1 ea 03 0f b6 89 c2 00 00 00 48 d3 e3 <42> 80 3c 2a 00 0f 85 03 16 00 00 48 89 58 10 48 c7 c0 08 ad c4 89
RSP: 0018:ffff88808bf77890 EFLAGS: 00010206
RAX: fffffffffffffff4 RBX: 00000000007ff000 RCX: 000000000000000c
RDX: 0000000000000000 RSI: ffffffff820534cd RDI: 0000000000000004
RBP: ffff88808bf77ac0 R08: 0000000000000000 R09: ffffed1015d06b7d
R10: ffffed1015d06b7c R11: ffff8880ae835be3 R12: 0000000000000000
R13: dffffc0000000000 R14: 00000000000007ff R15: ffff888086499488
FS:Â 0000000001162880(0000) GS:ffff8880ae800000(0000) knlGS:0000000000000000
CS:Â 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 000000009366b000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
Â? 0xffffffff81000000
Âdo_writepages+0xfa/0x2a0 mm/page-writeback.c:2344
Â__filemap_fdatawrite_range+0x2bc/0x3b0 mm/filemap.c:421
Âfilemap_write_and_wait_range mm/filemap.c:681 [inline]
Âfilemap_write_and_wait_range+0xfc/0x1d0 mm/filemap.c:675
Âext4_punch_hole+0x27d/0x1320 fs/ext4/inode.c:4314
Âext4_fallocate+0x419/0x2470 fs/ext4/extents.c:4889
Âvfs_fallocate+0x4aa/0xa50 fs/open.c:309
Âksys_fallocate+0x58/0xa0 fs/open.c:332
Â__do_sys_fallocate fs/open.c:340 [inline]
Â__se_sys_fallocate fs/open.c:338 [inline]
Â__x64_sys_fallocate+0x97/0xf0 fs/open.c:338
Âdo_syscall_64+0xfa/0x760 arch/x86/entry/common.c:290
Âentry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x440609
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 5b 14 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fffd7a50c58 EFLAGS: 00000246 ORIG_RAX: 000000000000011d
RAX: ffffffffffffffda RBX: 00007fffd7a50c60 RCX: 0000000000440609
RDX: 0000000000000000 RSI: 0000000100000003 RDI: 0000000000000003
RBP: 0000000000000004 R08: 0000000000000001 R09: 00007fffd7a50033
R10: 0000000028120001 R11: 0000000000000246 R12: 0000000000401ef0
R13: 0000000000401f80 R14: 0000000000000000 R15: 0000000000000000
Modules linked in:
---[ end trace 0ee46d2ea32148f5 ]---
RIP: 0010:mpage_map_and_submit_extent fs/ext4/inode.c:2557 [inline]
RIP: 0010:ext4_writepages+0x17b4/0x2e80 fs/ext4/inode.c:2911
Code: ff ff e8 1f cf b0 ff 48 8b 85 30 fe ff ff 48 8b 8d 00 fe ff ff 48 8d 78 10 48 89 fa 48 c1 ea 03 0f b6 89 c2 00 00 00 48 d3 e3 <42> 80 3c 2a 00 0f 85 03 16 00 00 48 89 58 10 48 c7 c0 08 ad c4 89
RSP: 0018:ffff88808bf77890 EFLAGS: 00010206
RAX: fffffffffffffff4 RBX: 00000000007ff000 RCX: 000000000000000c
RDX: 0000000000000000 RSI: ffffffff820534cd RDI: 0000000000000004
RBP: ffff88808bf77ac0 R08: 0000000000000000 R09: ffffed1015d06b7d
R10: ffffed1015d06b7c R11: ffff8880ae835be3 R12: 0000000000000000
R13: dffffc0000000000 R14: 00000000000007ff R15: ffff888086499488
FS:Â 0000000001162880(0000) GS:ffff8880ae800000(0000) knlGS:0000000000000000
CS:Â 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 000000009366b000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400


---
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