Re: [syzbot] [kernel?] general protection fault in proc_sys_call_handler

[syzbot <syzbot+2e65930fda17880da336@syzkaller.appspotmail.com>]

Hello,

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

write buf: \x13\x03, count: 64, tab: ffffffff8de3a458, proc_sys_call_handler
tab: ffffffff8de3a458, data: ffffffff90028f45, w: 1, proc_sys_call_handler
tab: ffffffff8de3a458, data: ffffffff90028f45, datalen: 6, maxlen: 65, procname: domainname, proc_do_uts_string
Oops: general protection fault, probably for non-canonical address 0xdffffc0000000001: 0000 [#1] PREEMPT SMP KASAN PTI
KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f]
CPU: 0 UID: 0 PID: 6507 Comm: syz-executor Not tainted 6.12.0-syzkaller-10299-g85a8463a4d24 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
RIP: 0010:get_uts kernel/utsname_sysctl.c:23 [inline]
RIP: 0010:proc_do_uts_string+0x1ea/0x5e0 kernel/utsname_sysctl.c:53
Code: 48 c1 ee 03 80 3c 0e 00 0f 85 76 03 00 00 48 8b 92 08 09 00 00 48 b9 00 00 00 00 00 fc ff df 48 8d 7a 08 48 89 fe 48 c1 ee 03 <80> 3c 0e 00 0f 85 32 03 00 00 48 be 00 00 00 00 00 fc ff df 48 2d
RSP: 0018:ffffc90003567460 EFLAGS: 00010202
RAX: ffffffff90028f45 RBX: ffffffff8de3a458 RCX: dffffc0000000000
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000008
RBP: 1ffff920006ace92 R08: 0000000000000001 R09: fffffbfff1b8e045
R10: ffffffff8dc7022f R11: 0000000000000002 R12: 0000000000000001
R13: ffffc900035674c0 R14: ffffc90003567520 R15: ffffffff8de3a460
FS:  0000000000000000(0000) GS:ffff8880b8600000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000056128a1406dd CR3: 000000002cf9c000 CR4: 00000000003526f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 proc_sys_call_handler+0x4b8/0x700 fs/proc/proc_sysctl.c:607
 __kernel_write_iter+0x318/0xa80 fs/read_write.c:612
 __kernel_write+0xf6/0x140 fs/read_write.c:632
 do_acct_process+0xcb0/0x14a0 kernel/acct.c:539
 acct_pin_kill+0x2d/0x100 kernel/acct.c:192
 pin_kill+0x194/0x7c0 fs/fs_pin.c:44
 mnt_pin_kill+0x61/0x1e0 fs/fs_pin.c:81
 cleanup_mnt+0x3ac/0x450 fs/namespace.c:1366
 task_work_run+0x14e/0x250 kernel/task_work.c:239
 exit_task_work include/linux/task_work.h:43 [inline]
 do_exit+0xadd/0x2d70 kernel/exit.c:938
 do_group_exit+0xd3/0x2a0 kernel/exit.c:1087
 get_signal+0x2576/0x2610 kernel/signal.c:3016
 arch_do_signal_or_restart+0x90/0x7e0 arch/x86/kernel/signal.c:337
 exit_to_user_mode_loop kernel/entry/common.c:111 [inline]
 exit_to_user_mode_prepare include/linux/entry-common.h:329 [inline]
 __syscall_exit_to_user_mode_work kernel/entry/common.c:207 [inline]
 syscall_exit_to_user_mode+0x150/0x2a0 kernel/entry/common.c:218
 do_syscall_64+0xda/0x250 arch/x86/entry/common.c:89
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7efcf8784597
Code: Unable to access opcode bytes at 0x7efcf878456d.
RSP: 002b:00007ffe839f29c8 EFLAGS: 00000202 ORIG_RAX: 0000000000000102
RAX: 0000000000000000 RBX: 00007ffe839f2a10 RCX: 00007efcf8784597
RDX: 00000000000001ff RSI: 00007ffe839f2a10 RDI: 00000000ffffff9c
RBP: 00007ffe839f29fc R08: 0000000000000005 R09: 00007ffe839f2765
R10: 0000000000000000 R11: 0000000000000202 R12: 0000000000000032
R13: 000000000002b475 R14: 00007ffe839f2a50 R15: 0000000000000258
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:get_uts kernel/utsname_sysctl.c:23 [inline]
RIP: 0010:proc_do_uts_string+0x1ea/0x5e0 kernel/utsname_sysctl.c:53
Code: 48 c1 ee 03 80 3c 0e 00 0f 85 76 03 00 00 48 8b 92 08 09 00 00 48 b9 00 00 00 00 00 fc ff df 48 8d 7a 08 48 89 fe 48 c1 ee 03 <80> 3c 0e 00 0f 85 32 03 00 00 48 be 00 00 00 00 00 fc ff df 48 2d
RSP: 0018:ffffc90003567460 EFLAGS: 00010202
RAX: ffffffff90028f45 RBX: ffffffff8de3a458 RCX: dffffc0000000000
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000008
RBP: 1ffff920006ace92 R08: 0000000000000001 R09: fffffbfff1b8e045
R10: ffffffff8dc7022f R11: 0000000000000002 R12: 0000000000000001
R13: ffffc900035674c0 R14: ffffc90003567520 R15: ffffffff8de3a460
FS:  0000000000000000(0000) GS:ffff8880b8600000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000056128a1406dd CR3: 0000000030060000 CR4: 00000000003526f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
----------------
Code disassembly (best guess):
   0:	48 c1 ee 03          	shr    $0x3,%rsi
   4:	80 3c 0e 00          	cmpb   $0x0,(%rsi,%rcx,1)
   8:	0f 85 76 03 00 00    	jne    0x384
   e:	48 8b 92 08 09 00 00 	mov    0x908(%rdx),%rdx
  15:	48 b9 00 00 00 00 00 	movabs $0xdffffc0000000000,%rcx
  1c:	fc ff df
  1f:	48 8d 7a 08          	lea    0x8(%rdx),%rdi
  23:	48 89 fe             	mov    %rdi,%rsi
  26:	48 c1 ee 03          	shr    $0x3,%rsi
* 2a:	80 3c 0e 00          	cmpb   $0x0,(%rsi,%rcx,1) <-- trapping instruction
  2e:	0f 85 32 03 00 00    	jne    0x366
  34:	48 be 00 00 00 00 00 	movabs $0xdffffc0000000000,%rsi
  3b:	fc ff df
  3e:	48                   	rex.W
  3f:	2d                   	.byte 0x2d


Tested on:

commit:         85a8463a utsname: debug ctl table for domainname
git tree:       https://github.com/ea1davis/linux proc/syz
console output: https://syzkaller.appspot.com/x/log.txt?x=16e566f8580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=e8d97faf7b870c89
dashboard link: https://syzkaller.appspot.com/bug?extid=2e65930fda17880da336
compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40

Note: no patches were applied.