[syzbot] [rds?] general protection fault in rds_tcp_accept_one

[syzbot <syzbot+96046021045ffe6d7709@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    9845cf73f7db Add linux-next specific files for 20260205
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=10ec4a5a580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=ac78ce3b6729749e
dashboard link: https://syzkaller.appspot.com/bug?extid=96046021045ffe6d7709
compiler:       Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=122acb22580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=149fc7fa580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/9f30334a2431/disk-9845cf73.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/0d58741a15a6/vmlinux-9845cf73.xz
kernel image: https://storage.googleapis.com/syzbot-assets/62204da1452c/bzImage-9845cf73.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+96046021045ffe6d7709@syzkaller.appspotmail.com

netdevsim netdevsim1 netdevsim3: set [1, 0] type 2 family 0 port 6081 - 0
Oops: general protection fault, probably for non-canonical address 0xdffffc0000000002: 0000 [#1] SMP KASAN PTI
KASAN: null-ptr-deref in range [0x0000000000000010-0x0000000000000017]
CPU: 1 UID: 0 PID: 3485 Comm: kworker/u8:8 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Workqueue: krdsd rds_tcp_accept_worker
RIP: 0010:rds_tcp_accept_one+0xa5b/0xd70 net/rds/tcp_listen.c:319
Code: 00 00 48 83 c3 18 48 89 d8 48 c1 e8 03 42 80 3c 28 00 74 08 48 89 df e8 63 a9 2f f7 48 8b 1b 48 83 c3 12 49 89 de 49 c1 ee 03 <43> 0f b6 04 2e 84 c0 0f 85 53 02 00 00 44 0f b6 2b bf 08 00 00 00
RSP: 0018:ffffc9000b64f9a0 EFLAGS: 00010202
RAX: 1ffff1100dacb173 RBX: 0000000000000012 RCX: 0000000000000000
RDX: 0000000000000006 RSI: ffffffff8e006fa9 RDI: 00000000ffffffff
RBP: ffffc9000b64fb18 R08: ffffffff903342b7 R09: 1ffffffff2066856
R10: dffffc0000000000 R11: fffffbfff2066857 R12: ffff88803286c000
R13: dffffc0000000000 R14: 0000000000000002 R15: 1ffff920016c9f3c
FS:  0000000000000000(0000) GS:ffff888125115000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f30359456b8 CR3: 00000000320ee000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 rds_tcp_accept_worker+0x1d/0x70 net/rds/tcp.c:524
 process_one_work+0x949/0x1650 kernel/workqueue.c:3279
 process_scheduled_works kernel/workqueue.c:3362 [inline]
 worker_thread+0xb46/0x1140 kernel/workqueue.c:3443
 kthread+0x388/0x470 kernel/kthread.c:467
 ret_from_fork+0x51e/0xb90 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:rds_tcp_accept_one+0xa5b/0xd70 net/rds/tcp_listen.c:319
Code: 00 00 48 83 c3 18 48 89 d8 48 c1 e8 03 42 80 3c 28 00 74 08 48 89 df e8 63 a9 2f f7 48 8b 1b 48 83 c3 12 49 89 de 49 c1 ee 03 <43> 0f b6 04 2e 84 c0 0f 85 53 02 00 00 44 0f b6 2b bf 08 00 00 00
RSP: 0018:ffffc9000b64f9a0 EFLAGS: 00010202
RAX: 1ffff1100dacb173 RBX: 0000000000000012 RCX: 0000000000000000
RDX: 0000000000000006 RSI: ffffffff8e006fa9 RDI: 00000000ffffffff
RBP: ffffc9000b64fb18 R08: ffffffff903342b7 R09: 1ffffffff2066856
R10: dffffc0000000000 R11: fffffbfff2066857 R12: ffff88803286c000
R13: dffffc0000000000 R14: 0000000000000002 R15: 1ffff920016c9f3c
FS:  0000000000000000(0000) GS:ffff888125115000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f303594da08 CR3: 000000000e74c000 CR4: 00000000003526f0
----------------
Code disassembly (best guess):
   0:	00 00                	add    %al,(%rax)
   2:	48 83 c3 18          	add    $0x18,%rbx
   6:	48 89 d8             	mov    %rbx,%rax
   9:	48 c1 e8 03          	shr    $0x3,%rax
   d:	42 80 3c 28 00       	cmpb   $0x0,(%rax,%r13,1)
  12:	74 08                	je     0x1c
  14:	48 89 df             	mov    %rbx,%rdi
  17:	e8 63 a9 2f f7       	call   0xf72fa97f
  1c:	48 8b 1b             	mov    (%rbx),%rbx
  1f:	48 83 c3 12          	add    $0x12,%rbx
  23:	49 89 de             	mov    %rbx,%r14
  26:	49 c1 ee 03          	shr    $0x3,%r14
* 2a:	43 0f b6 04 2e       	movzbl (%r14,%r13,1),%eax <-- trapping instruction
  2f:	84 c0                	test   %al,%al
  31:	0f 85 53 02 00 00    	jne    0x28a
  37:	44 0f b6 2b          	movzbl (%rbx),%r13d
  3b:	bf 08 00 00 00       	mov    $0x8,%edi


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