[moderation/CI] Re: net: devmem: improve cpu cost of RX token management

[syzbot ci <syzbot+ci6b3b9a0c3f217c63@syzkaller.appspotmail.com>]

syzbot ci has tested the following series

[v2] net: devmem: improve cpu cost of RX token management
https://lore.kernel.org/all/20250911-scratch-bobbyeshleman-devmem-tcp-token-upstream-v2-0-c80d735bd453@meta.com
* [PATCH net-next v2 1/3] net: devmem: rename tx_vec to vec in dmabuf binding
* [PATCH net-next v2 2/3] net: devmem: use niov array for token management
* [PATCH net-next v2 3/3] net: ethtool: prevent user from breaking devmem single-binding rule

and found the following issue:
general protection fault in sock_devmem_dontneed

Full report is available here:
https://ci.syzbot.org/series/40b2252a-f8bb-4cec-bfc1-2ff8a3c55336

***

general protection fault in sock_devmem_dontneed

tree:      net-next
URL:       https://kernel.googlesource.com/pub/scm/linux/kernel/git/netdev/net-next.git
base:      5adf6f2b9972dbb69f4dd11bae52ba251c64ecb7
arch:      amd64
compiler:  Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
config:    https://ci.syzbot.org/builds/2c30c608-f14f-4e6d-9772-cc5e129939fc/config
C repro:   https://ci.syzbot.org/findings/c89c36f8-4666-47d0-bc39-35662a268e4d/c_repro
syz repro: https://ci.syzbot.org/findings/c89c36f8-4666-47d0-bc39-35662a268e4d/syz_repro

Oops: general protection fault, probably for non-canonical address 0xdffffc0000000000: 0000 [#1] SMP KASAN PTI
KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
CPU: 1 UID: 0 PID: 6028 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:sock_devmem_dontneed+0x40b/0x910 net/core/sock.c:1112
Code: 8b 44 24 18 44 8b 20 44 03 64 24 14 48 8b 44 24 68 80 3c 18 00 74 08 4c 89 ef e8 f0 bb c9 f8 4d 8b 7d 00 4c 89 f8 48 c1 e8 03 <80> 3c 18 00 74 08 4c 89 ff e8 d7 bb c9 f8 4d 8b 2f 4c 89 e8 48 c1
RSP: 0018:ffffc90002987ac0 EFLAGS: 00010246
RAX: 0000000000000000 RBX: dffffc0000000000 RCX: 1ffff11020d27e78
RDX: ffff88810a039cc0 RSI: 0000000000000003 RDI: 0000000000000000
RBP: ffffc90002987c50 R08: ffffc90002987bdf R09: 0000000000000000
R10: ffffc90002987b60 R11: fffff52000530f7c R12: 0000000000000006
R13: ffff8881235cb710 R14: 0000000000000000 R15: 0000000000000000
FS:  000055555e866500(0000) GS:ffff8881a3c14000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b31b63fff CR3: 0000000027a20000 CR4: 00000000000006f0
Call Trace:
 <TASK>
 sk_setsockopt+0x682/0x2dc0 net/core/sock.c:1301
 do_sock_setsockopt+0x11b/0x1b0 net/socket.c:2340
 __sys_setsockopt net/socket.c:2369 [inline]
 __do_sys_setsockopt net/socket.c:2375 [inline]
 __se_sys_setsockopt net/socket.c:2372 [inline]
 __x64_sys_setsockopt+0x13f/0x1b0 net/socket.c:2372
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7faf24f8eba9
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:00007ffc3eb96018 EFLAGS: 00000246 ORIG_RAX: 0000000000000036
RAX: ffffffffffffffda RBX: 00007faf251d5fa0 RCX: 00007faf24f8eba9
RDX: 0000000000000050 RSI: 0000000000000001 RDI: 0000000000000003
RBP: 00007faf25011e19 R08: 0000000000000048 R09: 0000000000000000
R10: 0000200000000100 R11: 0000000000000246 R12: 0000000000000000
R13: 00007faf251d5fa0 R14: 00007faf251d5fa0 R15: 0000000000000005
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:sock_devmem_dontneed+0x40b/0x910 net/core/sock.c:1112
Code: 8b 44 24 18 44 8b 20 44 03 64 24 14 48 8b 44 24 68 80 3c 18 00 74 08 4c 89 ef e8 f0 bb c9 f8 4d 8b 7d 00 4c 89 f8 48 c1 e8 03 <80> 3c 18 00 74 08 4c 89 ff e8 d7 bb c9 f8 4d 8b 2f 4c 89 e8 48 c1
RSP: 0018:ffffc90002987ac0 EFLAGS: 00010246
RAX: 0000000000000000 RBX: dffffc0000000000 RCX: 1ffff11020d27e78
RDX: ffff88810a039cc0 RSI: 0000000000000003 RDI: 0000000000000000
RBP: ffffc90002987c50 R08: ffffc90002987bdf R09: 0000000000000000
R10: ffffc90002987b60 R11: fffff52000530f7c R12: 0000000000000006
R13: ffff8881235cb710 R14: 0000000000000000 R15: 0000000000000000
FS:  000055555e866500(0000) GS:ffff8881a3c14000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b31b63fff CR3: 0000000027a20000 CR4: 00000000000006f0
----------------
Code disassembly (best guess):
   0:	8b 44 24 18          	mov    0x18(%rsp),%eax
   4:	44 8b 20             	mov    (%rax),%r12d
   7:	44 03 64 24 14       	add    0x14(%rsp),%r12d
   c:	48 8b 44 24 68       	mov    0x68(%rsp),%rax
  11:	80 3c 18 00          	cmpb   $0x0,(%rax,%rbx,1)
  15:	74 08                	je     0x1f
  17:	4c 89 ef             	mov    %r13,%rdi
  1a:	e8 f0 bb c9 f8       	call   0xf8c9bc0f
  1f:	4d 8b 7d 00          	mov    0x0(%r13),%r15
  23:	4c 89 f8             	mov    %r15,%rax
  26:	48 c1 e8 03          	shr    $0x3,%rax
* 2a:	80 3c 18 00          	cmpb   $0x0,(%rax,%rbx,1) <-- trapping instruction
  2e:	74 08                	je     0x38
  30:	4c 89 ff             	mov    %r15,%rdi
  33:	e8 d7 bb c9 f8       	call   0xf8c9bc0f
  38:	4d 8b 2f             	mov    (%r15),%r13
  3b:	4c 89 e8             	mov    %r13,%rax
  3e:	48                   	rex.W
  3f:	c1                   	.byte 0xc1


***

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: syzbot@syzkaller.appspotmail.com

---
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