Re: [syzbot] [fs?] [mm?] stack segment fault in folio_wait_writeback

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On Sun, 13 Oct 2024 at 13:01, syzbot
<syzbot+8cb2efaaad483f65f56c@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
>
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit:    7234e2ea0edd Merge tag 'scsi-fixes' of git://git.kernel.or..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=157a085f980000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=7cd9e7e4a8a0a15b
> dashboard link: https://syzkaller.appspot.com/bug?extid=8cb2efaaad483f65f56c
> compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=146c7fd0580000
>
> Downloadable assets:
> disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/7feb34a89c2a/non_bootable_disk-7234e2ea.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/aa111520a0b7/vmlinux-7234e2ea.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/07889fadba3b/bzImage-7234e2ea.xz
> mounted in repro #1: https://storage.googleapis.com/syzbot-assets/178fe4a5f5e7/mount_1.gz
> mounted in repro #2: https://storage.googleapis.com/syzbot-assets/7847e1862894/mount_2.gz
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+8cb2efaaad483f65f56c@xxxxxxxxxxxxxxxxxxxxxxxxx
>
> loop0: detected capacity change from 0 to 256
> exFAT-fs (loop0): failed to load upcase table (idx : 0x00010000, chksum : 0xcc9b7de9, utbl_chksum : 0xe619d30d)
> Oops: stack segment: 0000 [#1] PREEMPT SMP KASAN NOPTI
> CPU: 0 UID: 0 PID: 5340 Comm: syz.0.50 Not tainted 6.12.0-rc2-syzkaller-00305-g7234e2ea0edd #0
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
> RIP: 0010:PageTail include/linux/page-flags.h:281 [inline]
> RIP: 0010:const_folio_flags include/linux/page-flags.h:309 [inline]
> RIP: 0010:folio_test_writeback include/linux/page-flags.h:555 [inline]
> RIP: 0010:folio_wait_writeback+0x2f/0x1e0 mm/page-writeback.c:3187
> Code: 41 57 41 56 41 55 41 54 53 48 83 ec 18 48 89 fb 49 bd 00 00 00 00 00 fc ff df e8 ac 7e c4 ff 4c 8d 73 08 4c 89 f5 48 c1 ed 03 <42> 80 7c 2d 00 00 74 08 4c 89 f7 e8 11 2f 2e 00 4d 8b 3e 4c 89 fe
> RSP: 0018:ffffc900025a7190 EFLAGS: 00010202
> RAX: ffffffff81d068a4 RBX: 0000000000000000 RCX: ffff888000c3c880
> RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000000
> RBP: 0000000000000001 R08: ffffffff81cc460e R09: 1ffffd4000003328
> R10: dffffc0000000000 R11: fffff94000003329 R12: dffffc0000000000
> R13: dffffc0000000000 R14: 0000000000000008 R15: 0000000000000001
> FS:  00007f7a897816c0(0000) GS:ffff88801fc00000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007f7a88a75c60 CR3: 000000003f406000 CR4: 0000000000352ef0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  <TASK>
>  __filemap_fdatawait_range+0x17c/0x2b0 mm/filemap.c:533
>  file_write_and_wait_range+0x1e3/0x280 mm/filemap.c:792
>  __generic_file_fsync+0x6f/0x1a0 fs/libfs.c:1528
>  exfat_file_fsync+0xf9/0x1d0 fs/exfat/file.c:524
>  exfat_file_write_iter+0x312/0x3f0 fs/exfat/file.c:608
>  iter_file_splice_write+0xbfa/0x1510 fs/splice.c:743
>  do_splice_from fs/splice.c:941 [inline]
>  direct_splice_actor+0x11b/0x220 fs/splice.c:1164
>  splice_direct_to_actor+0x586/0xc80 fs/splice.c:1108
>  do_splice_direct_actor fs/splice.c:1207 [inline]
>  do_splice_direct+0x289/0x3e0 fs/splice.c:1233
>  do_sendfile+0x561/0xe10 fs/read_write.c:1388
>  __do_sys_sendfile64 fs/read_write.c:1455 [inline]
>  __se_sys_sendfile64+0x17c/0x1e0 fs/read_write.c:1441
>  do_syscall_x64 arch/x86/entry/common.c:52 [inline]
>  do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7f7a8897dff9
> Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007f7a89781038 EFLAGS: 00000246 ORIG_RAX: 0000000000000028
> RAX: ffffffffffffffda RBX: 00007f7a88b35f80 RCX: 00007f7a8897dff9
> RDX: 0000000000000000 RSI: 0000000000000005 RDI: 0000000000000004
> RBP: 00007f7a889f0296 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000100001 R11: 0000000000000246 R12: 0000000000000000
> R13: 0000000000000000 R14: 00007f7a88b35f80 R15: 00007fffbdf78608
>  </TASK>
> Modules linked in:
> ---[ end trace 0000000000000000 ]---
> RIP: 0010:PageTail include/linux/page-flags.h:281 [inline]
> RIP: 0010:const_folio_flags include/linux/page-flags.h:309 [inline]
> RIP: 0010:folio_test_writeback include/linux/page-flags.h:555 [inline]
> RIP: 0010:folio_wait_writeback+0x2f/0x1e0 mm/page-writeback.c:3187
> Code: 41 57 41 56 41 55 41 54 53 48 83 ec 18 48 89 fb 49 bd 00 00 00 00 00 fc ff df e8 ac 7e c4 ff 4c 8d 73 08 4c 89 f5 48 c1 ed 03 <42> 80 7c 2d 00 00 74 08 4c 89 f7 e8 11 2f 2e 00 4d 8b 3e 4c 89 fe
> RSP: 0018:ffffc900025a7190 EFLAGS: 00010202
> RAX: ffffffff81d068a4 RBX: 0000000000000000 RCX: ffff888000c3c880
> RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000000
> RBP: 0000000000000001 R08: ffffffff81cc460e R09: 1ffffd4000003328
> R10: dffffc0000000000 R11: fffff94000003329 R12: dffffc0000000000
> R13: dffffc0000000000 R14: 0000000000000008 R15: 0000000000000001
> FS:  00007f7a897816c0(0000) GS:ffff88801fc00000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007f7a8975ff98 CR3: 000000003f406000 CR4: 0000000000352ef0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> ----------------
> Code disassembly (best guess):
>    0:   41 57                   push   %r15
>    2:   41 56                   push   %r14
>    4:   41 55                   push   %r13
>    6:   41 54                   push   %r12
>    8:   53                      push   %rbx
>    9:   48 83 ec 18             sub    $0x18,%rsp
>    d:   48 89 fb                mov    %rdi,%rbx
>   10:   49 bd 00 00 00 00 00    movabs $0xdffffc0000000000,%r13
>   17:   fc ff df
>   1a:   e8 ac 7e c4 ff          call   0xffc47ecb
>   1f:   4c 8d 73 08             lea    0x8(%rbx),%r14
>   23:   4c 89 f5                mov    %r14,%rbp
>   26:   48 c1 ed 03             shr    $0x3,%rbp
> * 2a:   42 80 7c 2d 00 00       cmpb   $0x0,0x0(%rbp,%r13,1) <-- trapping instruction

+tracing maintainers

Not sure how this instruction can cause stack segment violation.
The reproducer does something with raw tracepoints:
https://syzkaller.appspot.com/text?tag=ReproSyz&x=146c7fd0580000

Can raw tracepoints legally arbitrary corrupt kernel state?
If yes, is there some safe subset at least?


>   30:   74 08                   je     0x3a
>   32:   4c 89 f7                mov    %r14,%rdi
>   35:   e8 11 2f 2e 00          call   0x2e2f4b
>   3a:   4d 8b 3e                mov    (%r14),%r15
>   3d:   4c 89 fe                mov    %r15,%rsi
>
>
> ---
> 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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>
> If the report is already addressed, let syzbot know by replying with:
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>
> If you want syzbot to run the reproducer, reply with:
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>
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> (See the list of subsystem names on the web dashboard)
>
> If the report is a duplicate of another one, reply with:
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>
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> #syz undup




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