[syzbot ci] Re: io_uring: add kernel-managed buffer rings

[syzbot ci]

syzbot ci has tested the following series

[v2] io_uring: add kernel-managed buffer rings
https://lore.kernel.org/all/20260218025207.142...@gmail.com
* [PATCH v2 1/9] io_uring/memmap: chunk allocations in io_region_allocate_pages()
* [PATCH v2 2/9] io_uring/kbuf: add support for kernel-managed buffer rings
* [PATCH v2 3/9] io_uring/kbuf: support kernel-managed buffer rings in buffer selection
* [PATCH v2 4/9] io_uring/kbuf: add buffer ring pinning/unpinning
* [PATCH v2 5/9] io_uring/kbuf: return buffer id in buffer selection
* [PATCH v2 6/9] io_uring/kbuf: add recycling for kernel managed buffer rings
* [PATCH v2 7/9] io_uring/kbuf: add io_uring_is_kmbuf_ring()
* [PATCH v2 8/9] io_uring/kbuf: export io_ring_buffer_select()
* [PATCH v2 9/9] io_uring/cmd: set selected buffer index in __io_uring_cmd_done()

and found the following issue:
general protection fault in io_remove_buffers_legacy

Full report is available here:
https://ci.syzbot.org/series/ddeaf464-c69b-4166-b0cf-53c9d51e4820

***

general protection fault in io_remove_buffers_legacy

tree: torvalds
URL: https://kernel.googlesource.com/pub/scm/linux/kernel/git/torvalds/linux
base: 2961f841b025fb234860bac26dfb7fa7cb0fb122
arch: amd64
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
config: https://ci.syzbot.org/builds/ab5ad5aa-2757-4d66-a2c5-391a8417535d/config
C repro: https://ci.syzbot.org/findings/061747e2-36f1-499b-ac34-38cefffbce63/c_repro
syz repro: https://ci.syzbot.org/findings/061747e2-36f1-499b-ac34-38cefffbce63/syz_repro

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: 5967 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
RIP: 0010:__list_del_entry_valid_or_report+0x25/0x190 lib/list_debug.c:49
Code: 90 90 90 90 90 f3 0f 1e fa 41 57 41 56 41 55 41 54 53 48 89 fb 49 bd 00 00 00 00 00 fc ff df 48 83 c7 08 48 89 f8 48 c1 e8 03 <42> 80 3c 28 00 74 05 e8 df 8c 77 fd 4c 8b 7b 08 48 89 d8 48 c1 e8
RSP: 0018:ffffc900040a7b68 EFLAGS: 00010202
RAX: 0000000000000001 RBX: 0000000000000000 RCX: 1ffff11035ee2732
RDX: 1ffff11035ee2730 RSI: 00000000ffffffff RDI: 0000000000000008
RBP: dffffc0000000000 R08: ffff8881af7139b7 R09: 0000000000000000
R10: ffff8881af7139a0 R11: ffffed1035ee2737 R12: ffff8881af713980
R13: dffffc0000000000 R14: 00000000ffffffff R15: 0000000000000000
FS: 0000555560587500(0000) GS:ffff8882a9466000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000001000 CR3: 0000000175cd2000 CR4: 00000000000006f0
Call Trace:
<TASK>
__list_del_entry_valid include/linux/list.h:132 [inline]
__list_del_entry include/linux/list.h:223 [inline]
list_del include/linux/list.h:237 [inline]
io_remove_buffers_legacy+0x139/0x310 io_uring/kbuf.c:533
io_put_bl+0x62/0x120 io_uring/kbuf.c:548
io_register_pbuf_ring+0x6c0/0x7d0 io_uring/kbuf.c:855
__io_uring_register io_uring/register.c:838 [inline]
__do_sys_io_uring_register io_uring/register.c:1024 [inline]
__se_sys_io_uring_register+0xc3e/0x19a0 io_uring/register.c:1001
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f056859bf79
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fffd8dcfaf8 EFLAGS: 00000246 ORIG_RAX: 00000000000001ab
RAX: ffffffffffffffda RBX: 00007f0568815fa0 RCX: 00007f056859bf79
RDX: 0000200000000040 RSI: 0000000000000016 RDI: 0000000000000004
RBP: 00007f05686327e0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f0568815fac R14: 00007f0568815fa0 R15: 00007f0568815fa0
</TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:__list_del_entry_valid_or_report+0x25/0x190 lib/list_debug.c:49
Code: 90 90 90 90 90 f3 0f 1e fa 41 57 41 56 41 55 41 54 53 48 89 fb 49 bd 00 00 00 00 00 fc ff df 48 83 c7 08 48 89 f8 48 c1 e8 03 <42> 80 3c 28 00 74 05 e8 df 8c 77 fd 4c 8b 7b 08 48 89 d8 48 c1 e8
RSP: 0018:ffffc900040a7b68 EFLAGS: 00010202
RAX: 0000000000000001 RBX: 0000000000000000 RCX: 1ffff11035ee2732
RDX: 1ffff11035ee2730 RSI: 00000000ffffffff RDI: 0000000000000008
RBP: dffffc0000000000 R08: ffff8881af7139b7 R09: 0000000000000000
R10: ffff8881af7139a0 R11: ffffed1035ee2737 R12: ffff8881af713980
R13: dffffc0000000000 R14: 00000000ffffffff R15: 0000000000000000
FS: 0000555560587500(0000) GS:ffff8882a9466000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f25f1e17095 CR3: 0000000175cd2000 CR4: 00000000000006f0
----------------
Code disassembly (best guess):
0: 90 nop
1: 90 nop
2: 90 nop
3: 90 nop
4: 90 nop
5: f3 0f 1e fa endbr64
9: 41 57 push %r15
b: 41 56 push %r14
d: 41 55 push %r13
f: 41 54 push %r12
11: 53 push %rbx
12: 48 89 fb mov %rdi,%rbx
15: 49 bd 00 00 00 00 00 movabs $0xdffffc0000000000,%r13
1c: fc ff df
1f: 48 83 c7 08 add $0x8,%rdi
23: 48 89 f8 mov %rdi,%rax
26: 48 c1 e8 03 shr $0x3,%rax
* 2a: 42 80 3c 28 00 cmpb $0x0,(%rax,%r13,1) <-- trapping instruction
2f: 74 05 je 0x36
31: e8 df 8c 77 fd call 0xfd778d15
36: 4c 8b 7b 08 mov 0x8(%rbx),%r15
3a: 48 89 d8 mov %rbx,%rax
3d: 48 rex.W
3e: c1 .byte 0xc1
3f: e8 .byte 0xe8


***

If these findings have caused you to resend the series or submit a
separate fix, please add the following tag to your commit message:
Tested-by: syz...@syzkaller.appspotmail.com

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