[syzbot] [block?] general protection fault in bio_iov_iter_get_pages

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: be5d4872e528 Add linux-next specific files for 20250905
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=17896962580000
kernel config: https://syzkaller.appspot.com/x/.config?x=a726684450a7d788
dashboard link: https://syzkaller.appspot.com/bug?extid=b253ade8e1751d90a7a9
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=10496962580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=14a98962580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/f67121360b62/disk-be5d4872.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/4f666ca2e57f/vmlinux-be5d4872.xz
kernel image: https://storage.googleapis.com/syzbot-assets/e86b794b985e/bzImage-be5d4872.xz

The issue was bisected to:

commit db076b5db550aa34169dceee81d0974c7b2a2482
Author: David Hildenbrand <da...@redhat.com>
Date: Mon Sep 1 15:03:40 2025 +0000

mm/gup: remove record_subpages()

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=15a0b312580000
final oops: https://syzkaller.appspot.com/x/report.txt?x=17a0b312580000
console output: https://syzkaller.appspot.com/x/log.txt?x=13a0b312580000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+b253ad...@syzkaller.appspotmail.com
Fixes: db076b5db550 ("mm/gup: remove record_subpages()")

Oops: general protection fault, probably for non-canonical address 0xdffffc0000000001: 0000 [#1] SMP KASAN PTI
KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f]
CPU: 1 UID: 0 PID: 6063 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
RIP: 0010:_compound_head include/linux/page-flags.h:284 [inline]
RIP: 0010:__bio_iov_iter_get_pages block/bio.c:1258 [inline]
RIP: 0010:bio_iov_iter_get_pages+0x5b2/0x11c0 block/bio.c:1336
Code: 9c 24 20 01 00 00 48 89 d8 48 c1 e8 03 42 80 3c 20 00 74 08 48 89 df e8 0c c9 7c fd 48 8b 1b 4c 8d 73 08 4c 89 f0 48 c1 e8 03 <42> 80 3c 20 00 74 08 4c 89 f7 e8 ef c8 7c fd 4d 8b 3e 4c 89 fe 48
RSP: 0018:ffffc90002f773e0 EFLAGS: 00010202
RAX: 0000000000000001 RBX: 0000000000000000 RCX: ffff88807bfd0000
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: ffffc90002f77590 R08: 0000000000000000 R09: ffffffff84a7d3b5
R10: dffffc0000000000 R11: fffff94000329b51 R12: dffffc0000000000
R13: ffff888078cd0294 R14: 0000000000000008 R15: 00000000000000f0
FS: 0000555567d13500(0000) GS:ffff888125af9000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f9a3134c000 CR3: 0000000074d2a000 CR4: 00000000003526f0
Call Trace:
<TASK>
__blkdev_direct_IO+0x60b/0xee0 block/fops.c:215
blkdev_direct_IO+0x120f/0x1730 block/fops.c:434
blkdev_direct_write+0x7c/0x140 block/fops.c:719
blkdev_write_iter+0x547/0x710 block/fops.c:787
aio_write+0x535/0x7a0 fs/aio.c:1634
__io_submit_one fs/aio.c:-1 [inline]
io_submit_one+0x78b/0x1310 fs/aio.c:2053
__do_sys_io_submit fs/aio.c:2112 [inline]
__se_sys_io_submit+0x185/0x2f0 fs/aio.c:2082
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f9a3058ebe9
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:00007ffdf48caa48 EFLAGS: 00000246 ORIG_RAX: 00000000000000d1
RAX: ffffffffffffffda RBX: 00007f9a307c5fa0 RCX: 00007f9a3058ebe9
RDX: 00002000000000c0 RSI: 00000000000000f3 RDI: 00007f9a3134c000
RBP: 00007f9a30611e19 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f9a307c5fa0 R14: 00007f9a307c5fa0 R15: 0000000000000003
</TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:_compound_head include/linux/page-flags.h:284 [inline]
RIP: 0010:__bio_iov_iter_get_pages block/bio.c:1258 [inline]
RIP: 0010:bio_iov_iter_get_pages+0x5b2/0x11c0 block/bio.c:1336
Code: 9c 24 20 01 00 00 48 89 d8 48 c1 e8 03 42 80 3c 20 00 74 08 48 89 df e8 0c c9 7c fd 48 8b 1b 4c 8d 73 08 4c 89 f0 48 c1 e8 03 <42> 80 3c 20 00 74 08 4c 89 f7 e8 ef c8 7c fd 4d 8b 3e 4c 89 fe 48
RSP: 0018:ffffc90002f773e0 EFLAGS: 00010202
RAX: 0000000000000001 RBX: 0000000000000000 RCX: ffff88807bfd0000
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: ffffc90002f77590 R08: 0000000000000000 R09: ffffffff84a7d3b5
R10: dffffc0000000000 R11: fffff94000329b51 R12: dffffc0000000000
R13: ffff888078cd0294 R14: 0000000000000008 R15: 00000000000000f0
FS: 0000555567d13500(0000) GS:ffff8881259f9000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ffe8453cfd8 CR3: 0000000074d2a000 CR4: 00000000003526f0
----------------
Code disassembly (best guess):
0: 9c pushf
1: 24 20 and $0x20,%al
3: 01 00 add %eax,(%rax)
5: 00 48 89 add %cl,-0x77(%rax)
8: d8 48 c1 fmuls -0x3f(%rax)
b: e8 03 42 80 3c call 0x3c804213
10: 20 00 and %al,(%rax)
12: 74 08 je 0x1c
14: 48 89 df mov %rbx,%rdi
17: e8 0c c9 7c fd call 0xfd7cc928
1c: 48 8b 1b mov (%rbx),%rbx
1f: 4c 8d 73 08 lea 0x8(%rbx),%r14
23: 4c 89 f0 mov %r14,%rax
26: 48 c1 e8 03 shr $0x3,%rax
* 2a: 42 80 3c 20 00 cmpb $0x0,(%rax,%r12,1) <-- trapping instruction
2f: 74 08 je 0x39
31: 4c 89 f7 mov %r14,%rdi
34: e8 ef c8 7c fd call 0xfd7cc928
39: 4d 8b 3e mov (%r14),%r15
3c: 4c 89 fe mov %r15,%rsi
3f: 48 rex.W


---
This report is generated by a bot. It may contain errors.
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For information about bisection process see: https://goo.gl/tpsmEJ#bisection

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

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#syz test: git://repo/address.git branch-or-commit-hash
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#syz undup

[Hillf Danton]

> Date: Sun, 07 Sep 2025 00:11:35 -0700 [thread overview]

> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit: be5d4872e528 Add linux-next specific files for 20250905
> git tree: linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=17896962580000
> kernel config: https://syzkaller.appspot.com/x/.config?x=a726684450a7d788
> dashboard link: https://syzkaller.appspot.com/bug?extid=b253ade8e1751d90a7a9
> compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=10496962580000
> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=14a98962580000

#syz test

--- x/mm/gup.c
+++ y/mm/gup.c
@@ -2981,6 +2981,7 @@ static int gup_fast_pmd_leaf(pmd_t orig,
return 0;
}

+ pages += *nr;
*nr += refs;
for (; refs; refs--)
*(pages++) = page++;
@@ -3024,6 +3025,7 @@ static int gup_fast_pud_leaf(pud_t orig,
return 0;
}

+ pages += *nr;
*nr += refs;
for (; refs; refs--)
*(pages++) = page++;
--

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+b253ad...@syzkaller.appspotmail.com
Tested-by: syzbot+b253ad...@syzkaller.appspotmail.com

Tested on:

commit: be5d4872 Add linux-next specific files for 20250905
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=17e2b312580000

kernel config: https://syzkaller.appspot.com/x/.config?x=a726684450a7d788
dashboard link: https://syzkaller.appspot.com/bug?extid=b253ade8e1751d90a7a9
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8

patch: https://syzkaller.appspot.com/x/patch.diff?x=14be8562580000

Note: testing is done by a robot and is best-effort only.