[syzbot ci] Re: net: devmem: improve cpu cost of RX token management

[syzbot ci <syzbot+ci4cf7c6dde1c8793c@syzkaller.appspotmail.com>]

syzbot ci has tested the following series

[v1] net: devmem: improve cpu cost of RX token management
https://lore.kernel.org/all/20250902-scratch-bobbyeshleman-devmem-tcp-token-upstream-v1-0-d946169b5550@meta.com
* [PATCH net-next 1/2] net: devmem: rename tx_vec to vec in dmabuf binding
* [PATCH net-next 2/2] net: devmem: use niov array for token management

and found the following issue:
general protection fault in sock_devmem_dontneed

Full report is available here:
https://ci.syzbot.org/series/c0dc7223-4222-461c-b04b-b6f0004c7509

***

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:      864ecc4a6dade82d3f70eab43dad0e277aa6fc78
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/6c521908-0a73-48bc-a0fd-2576cf868361/config
C repro:   https://ci.syzbot.org/findings/9374f388-d643-42ea-831b-872eb5000b3c/c_repro
syz repro: https://ci.syzbot.org/findings/9374f388-d643-42ea-831b-872eb5000b3c/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: 0 UID: 0 PID: 5993 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+0x3fd/0x960 net/core/sock.c:1112
Code: 8b 44 24 40 44 8b 28 44 03 6c 24 14 48 8b 44 24 20 42 80 3c 20 00 74 08 4c 89 ff e8 4d eb c9 f8 4d 8b 3f 4c 89 f8 48 c1 e8 03 <42> 80 3c 20 00 74 08 4c 89 ff e8 34 eb c9 f8 4d 8b 3f 4c 89 f8 48
RSP: 0018:ffffc90001c4fac0 EFLAGS: 00010246
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 1ffff11004ddcfe0
RDX: ffff88801f6a8000 RSI: 0000000000000400 RDI: 0000000000000000
RBP: ffffc90001c4fc50 R08: ffffc90001c4fbdf R09: 0000000000000000
R10: ffffc90001c4fb60 R11: fffff52000389f7c R12: dffffc0000000000
R13: 00000000ffffffff R14: 0000000000000000 R15: 0000000000000000
FS:  000055558634d500(0000) GS:ffff8880b8614000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b30e63fff CR3: 0000000026b68000 CR4: 00000000000006f0
Call Trace:
 <TASK>
 sk_setsockopt+0x682/0x2dc0 net/core/sock.c:1302
 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: 0033:0x7fea2bb8ebe9
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:00007ffc81c63348 EFLAGS: 00000246 ORIG_RAX: 0000000000000036
RAX: ffffffffffffffda RBX: 00007fea2bdc5fa0 RCX: 00007fea2bb8ebe9
RDX: 0000000000000050 RSI: 0000000000000001 RDI: 0000000000000003
RBP: 00007fea2bc11e19 R08: 0000000000000048 R09: 0000000000000000
R10: 0000200000000100 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fea2bdc5fa0 R14: 00007fea2bdc5fa0 R15: 0000000000000005
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:sock_devmem_dontneed+0x3fd/0x960 net/core/sock.c:1112
Code: 8b 44 24 40 44 8b 28 44 03 6c 24 14 48 8b 44 24 20 42 80 3c 20 00 74 08 4c 89 ff e8 4d eb c9 f8 4d 8b 3f 4c 89 f8 48 c1 e8 03 <42> 80 3c 20 00 74 08 4c 89 ff e8 34 eb c9 f8 4d 8b 3f 4c 89 f8 48
RSP: 0018:ffffc90001c4fac0 EFLAGS: 00010246
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 1ffff11004ddcfe0
RDX: ffff88801f6a8000 RSI: 0000000000000400 RDI: 0000000000000000
RBP: ffffc90001c4fc50 R08: ffffc90001c4fbdf R09: 0000000000000000
R10: ffffc90001c4fb60 R11: fffff52000389f7c R12: dffffc0000000000
R13: 00000000ffffffff R14: 0000000000000000 R15: 0000000000000000
FS:  000055558634d500(0000) GS:ffff8880b8614000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b30e63fff CR3: 0000000026b68000 CR4: 00000000000006f0
----------------
Code disassembly (best guess):
   0:	8b 44 24 40          	mov    0x40(%rsp),%eax
   4:	44 8b 28             	mov    (%rax),%r13d
   7:	44 03 6c 24 14       	add    0x14(%rsp),%r13d
   c:	48 8b 44 24 20       	mov    0x20(%rsp),%rax
  11:	42 80 3c 20 00       	cmpb   $0x0,(%rax,%r12,1)
  16:	74 08                	je     0x20
  18:	4c 89 ff             	mov    %r15,%rdi
  1b:	e8 4d eb c9 f8       	call   0xf8c9eb6d
  20:	4d 8b 3f             	mov    (%r15),%r15
  23:	4c 89 f8             	mov    %r15,%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 ff             	mov    %r15,%rdi
  34:	e8 34 eb c9 f8       	call   0xf8c9eb6d
  39:	4d 8b 3f             	mov    (%r15),%r15
  3c:	4c 89 f8             	mov    %r15,%rax
  3f:	48                   	rex.W


***

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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