Re: [syzbot] [rdma?] KASAN: slab-use-after-free Read in ucma_create_uevent

[syzbot <syzbot+a6ffe86390c8a6afc818@syzkaller.appspotmail.com>]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
general protection fault in ucma_cleanup_mc_events

syz1: rxe_newlink: already configured on syz_tun
Oops: general protection fault, probably for non-canonical address 0xdffffc0000000083: 0000 [#1] SMP KASAN NOPTI
KASAN: null-ptr-deref in range [0x0000000000000418-0x000000000000041f]
CPU: 1 UID: 0 PID: 6579 Comm: syz.0.24 Not tainted 6.16.0-rc7-syzkaller-g2942242dde89-dirty #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
RIP: 0010:__mutex_lock_common kernel/locking/mutex.c:581 [inline]
RIP: 0010:__mutex_lock+0x14f/0xb90 kernel/locking/mutex.c:747
Code: d0 7c 08 84 d2 0f 85 ab 07 00 00 8b 35 1a 59 56 0f 85 f6 75 29 48 b8 00 00 00 00 00 fc ff df 48 8d 7b 60 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f 85 93 07 00 00 48 3b 5b 60 0f 85 e0 01 00 00 bf 01
RSP: 0018:ffffc900016df8b0 EFLAGS: 00010202

RAX: dffffc0000000000 RBX: 00000000000003b8 RCX: 1ffffffff35c0a00
RDX: 0000000000000083 RSI: 0000000000000000 RDI: 0000000000000418
RBP: ffffc900016df9f0 R08: ffffffff889fb8fd R09: fffff520002dbf35
R10: ffffc900016dfa10 R11: 0000000000000001 R12: dffffc0000000000
R13: ffffc900016df930 R14: 0000000000000000 R15: 1ffff920002dbf20
FS:  00007f6bbe81d6c0(0000) GS:ffff8880d6812000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 000000002a054000 CR4: 0000000000352ef0
Call Trace:
 <TASK>
 ucma_cleanup_mc_events+0x5d/0x490 drivers/infiniband/core/ucma.c:518
 ucma_process_join+0x966/0xad0 drivers/infiniband/core/ucma.c:1519
 ucma_join_multicast+0xe8/0x160 drivers/infiniband/core/ucma.c:1567
 ucma_write+0x1fb/0x330 drivers/infiniband/core/ucma.c:1748
 vfs_write+0x29d/0x1150 fs/read_write.c:684
 ksys_write+0x1f8/0x250 fs/read_write.c:738
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xcd/0x4c0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f6bbd98e929
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:00007f6bbe81d038 EFLAGS: 00000246
 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f6bbdbb5fa0 RCX: 00007f6bbd98e929
RDX: 00000000000000a0 RSI: 0000200000000900 RDI: 0000000000000004
RBP: 00007f6bbda10b39 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007f6bbdbb5fa0 R15: 00007fff295a4748
 </TASK>
Modules linked in:

---[ end trace 0000000000000000 ]---
RIP: 0010:__mutex_lock_common kernel/locking/mutex.c:581 [inline]
RIP: 0010:__mutex_lock+0x14f/0xb90 kernel/locking/mutex.c:747
Code: d0 7c 08 84 d2 0f 85 ab 07 00 00 8b 35 1a 59 56 0f 85 f6 75 29 48 b8 00 00 00 00 00 fc ff df 48 8d 7b 60 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f 85 93 07 00 00 48 3b 5b 60 0f 85 e0 01 00 00 bf 01
RSP: 0018:ffffc900016df8b0 EFLAGS: 00010202

RAX: dffffc0000000000 RBX: 00000000000003b8 RCX: 1ffffffff35c0a00
----------------
Code disassembly (best guess):
   0:	d0 7c 08 84          	sarb   -0x7c(%rax,%rcx,1)
   4:	d2 0f                	rorb   %cl,(%rdi)
   6:	85 ab 07 00 00 8b    	test   %ebp,-0x74fffff9(%rbx)
   c:	35 1a 59 56 0f       	xor    $0xf56591a,%eax
  11:	85 f6                	test   %esi,%esi
  13:	75 29                	jne    0x3e
  15:	48 b8 00 00 00 00 00 	movabs $0xdffffc0000000000,%rax
  1c:	fc ff df
  1f:	48 8d 7b 60          	lea    0x60(%rbx),%rdi
  23:	48 89 fa             	mov    %rdi,%rdx
  26:	48 c1 ea 03          	shr    $0x3,%rdx
* 2a:	80 3c 02 00          	cmpb   $0x0,(%rdx,%rax,1) <-- trapping instruction
  2e:	0f 85 93 07 00 00    	jne    0x7c7
  34:	48 3b 5b 60          	cmp    0x60(%rbx),%rbx
  38:	0f 85 e0 01 00 00    	jne    0x21e
  3e:	bf                   	.byte 0xbf
  3f:	01                   	.byte 0x1


Tested on:

commit:         2942242d Merge tag 'mm-hotfixes-stable-2025-07-24-18-0..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=133490a2580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=c445d2891161cc81
dashboard link: https://syzkaller.appspot.com/bug?extid=a6ffe86390c8a6afc818
compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
patch:          https://syzkaller.appspot.com/x/patch.diff?x=17f994f0580000