[syzbot] [kernel?] WARNING in posixtimer_send_sigqueue

[syzbot] [kernel?] WARNING in posixtimer_send_sigqueue

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    929beafbe7ac Add linux-next specific files for 20241108
git tree:       linux-next
console+strace: https://syzkaller.appspot.com/x/log.txt?x=10f714e8580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=75175323f2078363
dashboard link: https://syzkaller.appspot.com/bug?extid=852e935b899bde73626e
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=14f714e8580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1657b0c0580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/9705ecb6a595/disk-929beafb.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/dbdd1f64b9b8/vmlinux-929beafb.xz
kernel image: https://storage.googleapis.com/syzbot-assets/3f70d07a929b/bzImage-929beafb.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+852e935b899bde73626e@syzkaller.appspotmail.com

------------[ cut here ]------------
WARNING: CPU: 0 PID: 5854 at kernel/signal.c:2008 posixtimer_send_sigqueue+0x9da/0xbc0 kernel/signal.c:2008
Modules linked in:
CPU: 0 UID: 0 PID: 5854 Comm: syz-executor139 Not tainted 6.12.0-rc6-next-20241108-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/30/2024
RIP: 0010:posixtimer_send_sigqueue+0x9da/0xbc0 kernel/signal.c:2008
Code: df 80 3c 08 00 74 08 48 89 df e8 c1 ad a5 00 4c 89 2b eb 51 e8 a7 32 3b 00 41 be 02 00 00 00 e9 e9 fd ff ff e8 97 32 3b 00 90 <0f> 0b 90 e9 f2 fa ff ff 4c 89 ef e8 86 33 5a 03 84 c0 0f 84 aa 01
RSP: 0018:ffffc90000007bc0 EFLAGS: 00010006
RAX: ffffffff81644979 RBX: 0000000000000000 RCX: ffff888027dd8000
RDX: 0000000000010000 RSI: 000000000000001e RDI: 0000000000000009
RBP: ffffc90000007cc0 R08: ffffffff816450cc R09: 1ffffffff2857112
R10: dffffc0000000000 R11: fffffbfff2857113 R12: ffff8880203f6264
R13: 1ffff1100407ec4c R14: ffff8880203f61e0 R15: ffff8880203f62a0
FS:  0000555573d1f480(0000) GS:ffff8880b8600000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f61ecbdf388 CR3: 0000000036944000 CR4: 00000000003526f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <IRQ>
 alarm_handle_timer+0x2f/0x60 kernel/time/alarmtimer.c:537
 alarmtimer_fired+0x173/0x410 kernel/time/alarmtimer.c:205
 __run_hrtimer kernel/time/hrtimer.c:1739 [inline]
 __hrtimer_run_queues+0x59b/0xd50 kernel/time/hrtimer.c:1803
 hrtimer_interrupt+0x403/0xa40 kernel/time/hrtimer.c:1865
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1038 [inline]
 __sysvec_apic_timer_interrupt+0x110/0x420 arch/x86/kernel/apic/apic.c:1055
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1049 [inline]
 sysvec_apic_timer_interrupt+0xa1/0xc0 arch/x86/kernel/apic/apic.c:1049
 </IRQ>
 <TASK>
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:702
RIP: 0010:lock_acquire+0x264/0x550 kernel/locking/lockdep.c:5853
Code: 2b 00 74 08 4c 89 f7 e8 7a 52 8f 00 f6 44 24 61 02 0f 85 85 01 00 00 41 f7 c7 00 02 00 00 74 01 fb 48 c7 44 24 40 0e 36 e0 45 <4b> c7 44 25 00 00 00 00 00 43 c7 44 25 09 00 00 00 00 43 c7 44 25
RSP: 0018:ffffc90003bf6ea0 EFLAGS: 00000206
RAX: 0000000000000001 RBX: 1ffff9200077ede0 RCX: ffff888027dd8ad8
RDX: dffffc0000000000 RSI: ffffffff8c0aea60 RDI: ffffffff8c605b60
RBP: ffffc90003bf6fe8 R08: ffffffff942b88b7 R09: 1ffffffff2857116
R10: dffffc0000000000 R11: fffffbfff2857117 R12: 1ffff9200077eddc
R13: dffffc0000000000 R14: ffffc90003bf6f00 R15: 0000000000000246
 down_read_killable+0xca/0xd30 kernel/locking/rwsem.c:1547
 mmap_read_lock_killable include/linux/mmap_lock.h:198 [inline]
 __get_user_pages_locked mm/gup.c:1726 [inline]
 get_dump_page+0xe2/0x2f0 mm/gup.c:2269
 dump_user_range+0x14d/0x970 fs/coredump.c:943
 elf_core_dump+0x3e9f/0x4790 fs/binfmt_elf.c:2127
 do_coredump+0x214b/0x2e60 fs/coredump.c:758
 get_signal+0x140b/0x1750 kernel/signal.c:2995
 arch_do_signal_or_restart+0x96/0x860 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]
 irqentry_exit_to_user_mode+0x7e/0x250 kernel/entry/common.c:231
 exc_page_fault+0x590/0x8c0 arch/x86/mm/fault.c:1542
 asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:623
RIP: 0033:0x7f61ecb6431e
Code: fd d7 c9 0f bc d1 c5 fe 7f 27 c5 fe 7f 6f 20 c5 fe 7f 77 40 c5 fe 7f 7f 60 49 83 c0 1f 49 29 d0 48 8d 7c 17 61 e9 d2 04 00 00 <c5> fe 6f 1e c5 fe 6f 56 20 c5 fd 74 cb c5 fd d7 d1 49 83 f8 21 0f
RSP: 002b:00007ffd91b57128 EFLAGS: 00010287
RAX: 00007ffd91b57130 RBX: 00007ffd91b57130 RCX: 0000000000000000
RDX: 00000000000000e0 RSI: 0000000000000000 RDI: 00007ffd91b57130
RBP: 00007ffd91b57280 R08: 00000000000000e0 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000206 R12: 0000000000000000
R13: 00000000000f4240 R14: 00000000000140b7 R15: 00007ffd91b57264
 </TASK>
----------------
Code disassembly (best guess):
   0:	2b 00                	sub    (%rax),%eax
   2:	74 08                	je     0xc
   4:	4c 89 f7             	mov    %r14,%rdi
   7:	e8 7a 52 8f 00       	call   0x8f5286
   c:	f6 44 24 61 02       	testb  $0x2,0x61(%rsp)
  11:	0f 85 85 01 00 00    	jne    0x19c
  17:	41 f7 c7 00 02 00 00 	test   $0x200,%r15d
  1e:	74 01                	je     0x21
  20:	fb                   	sti
  21:	48 c7 44 24 40 0e 36 	movq   $0x45e0360e,0x40(%rsp)
  28:	e0 45
* 2a:	4b c7 44 25 00 00 00 	movq   $0x0,0x0(%r13,%r12,1) <-- trapping instruction
  31:	00 00
  33:	43 c7 44 25 09 00 00 	movl   $0x0,0x9(%r13,%r12,1)
  3a:	00 00
  3c:	43                   	rex.XB
  3d:	c7                   	.byte 0xc7
  3e:	44                   	rex.R
  3f:	25                   	.byte 0x25


---
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Re: [syzbot] [kernel?] WARNING in posixtimer_send_sigqueue

[Frederic Weisbecker]

Le Wed, Nov 13, 2024 at 04:52:22PM -0800, syzbot a écrit :
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    929beafbe7ac Add linux-next specific files for 20241108
> git tree:       linux-next
> console+strace: https://syzkaller.appspot.com/x/log.txt?x=10f714e8580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=75175323f2078363
> dashboard link: https://syzkaller.appspot.com/bug?extid=852e935b899bde73626e
> compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=14f714e8580000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1657b0c0580000
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/9705ecb6a595/disk-929beafb.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/dbdd1f64b9b8/vmlinux-929beafb.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/3f70d07a929b/bzImage-929beafb.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+852e935b899bde73626e@syzkaller.appspotmail.com
> 
> ------------[ cut here ]------------
> WARNING: CPU: 0 PID: 5854 at kernel/signal.c:2008
> posixtimer_send_sigqueue+0x9da/0xbc0 kernel/signal.c:2008

That's because prepare_signal() does not only return false when the signal is
ignored but also when the task group is exiting. It's possible that the task
enters in do_exit() with pending signal and then the timer is reset and a new
signal is queued before the sighand dies.

This should fix it:

diff --git a/kernel/signal.c b/kernel/signal.c
index cbf70c808969..10b464b9d91f 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -2003,9 +2003,15 @@ void posixtimer_send_sigqueue(struct k_itimer *tmr)
 	if (!prepare_signal(sig, t, false)) {
 		result = TRACE_SIGNAL_IGNORED;
 
-		/* Paranoia check. Try to survive. */
-		if (WARN_ON_ONCE(!list_empty(&q->list)))
+		if (!list_empty(&q->list)) {
+			/*
+			 * If task group is exiting with the signal already pending,
+			 * wait for __exit_signal() to do its job. Otherwise if
+			 * ignored, it's not supposed to be queued. Try to survive.
+			 */
+			WARN_ON_ONCE(!(t->signal->flags & SIGNAL_GROUP_EXIT));
 			goto out;
+		}
 
 		/* Periodic timers with SIG_IGN are queued on the ignored list */
 		if (tmr->it_sig_periodic) {

Re: [syzbot] [kernel?] WARNING in posixtimer_send_sigqueue

[Hillf Danton]

On Thu, 14 Nov 2024 17:49:23 +0100 Frederic Weisbecker <frederic@kernel.org>
Le Wed, Nov 13, 2024 at 04:52:22PM -0800
> > syzbot found the following issue on:
> > 
> > HEAD commit:    929beafbe7ac Add linux-next specific files for 20241108
> > git tree:       linux-next
> > console+strace: https://syzkaller.appspot.com/x/log.txt?x=10f714e8580000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=75175323f2078363
> > dashboard link: https://syzkaller.appspot.com/bug?extid=852e935b899bde73626e
> > compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
> > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=14f714e8580000
> > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1657b0c0580000
> > 
> > Downloadable assets:
> > disk image: https://storage.googleapis.com/syzbot-assets/9705ecb6a595/disk-929beafb.raw.xz
> > vmlinux: https://storage.googleapis.com/syzbot-assets/dbdd1f64b9b8/vmlinux-929beafb.xz
> > kernel image: https://storage.googleapis.com/syzbot-assets/3f70d07a929b/bzImage-929beafb.xz
> > 
> > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > Reported-by: syzbot+852e935b899bde73626e@syzkaller.appspotmail.com
> > 
> > ------------[ cut here ]------------
> > WARNING: CPU: 0 PID: 5854 at kernel/signal.c:2008
> > posixtimer_send_sigqueue+0x9da/0xbc0 kernel/signal.c:2008
> 
> That's because prepare_signal() does not only return false when the signal is
> ignored but also when the task group is exiting. It's possible that the task
> enters in do_exit() with pending signal and then the timer is reset and a new
> signal is queued before the sighand dies.
> 
> This should fix it:
> 
> diff --git a/kernel/signal.c b/kernel/signal.c
> index cbf70c808969..10b464b9d91f 100644
> --- a/kernel/signal.c
> +++ b/kernel/signal.c
> @@ -2003,9 +2003,15 @@ void posixtimer_send_sigqueue(struct k_itimer *tmr)
>  	if (!prepare_signal(sig, t, false)) {
>  		result = TRACE_SIGNAL_IGNORED;
>  
> -		/* Paranoia check. Try to survive. */
> -		if (WARN_ON_ONCE(!list_empty(&q->list)))
> +		if (!list_empty(&q->list)) {
> +			/*
> +			 * If task group is exiting with the signal already pending,
> +			 * wait for __exit_signal() to do its job. Otherwise if
> +			 * ignored, it's not supposed to be queued. Try to survive.
> +			 */
> +			WARN_ON_ONCE(!(t->signal->flags & SIGNAL_GROUP_EXIT));
>  			goto out;
> +		}
>  
>  		/* Periodic timers with SIG_IGN are queued on the ignored list */
>  		if (tmr->it_sig_periodic) {
> 
Test Frederic's patch on top of the next tree.

#syz test

--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -2004,9 +2004,15 @@ void posixtimer_send_sigqueue(struct k_i
 	if (!prepare_signal(sig, t, false)) {
 		result = TRACE_SIGNAL_IGNORED;
 
-		/* Paranoia check. Try to survive. */
-		if (WARN_ON_ONCE(!list_empty(&q->list)))
+		if (!list_empty(&q->list)) {
+			/*
+			 * If task group is exiting with the signal already pending,
+			 * wait for __exit_signal() to do its job. Otherwise if
+			 * ignored, it's not supposed to be queued. Try to survive.
+			 */
+			WARN_ON_ONCE(!(t->signal->flags & SIGNAL_GROUP_EXIT));
 			goto out;
+		}
 
 		/* Periodic timers with SIG_IGN are queued on the ignored list */
 		if (tmr->it_sig_periodic) {
--

Re: [syzbot] [kernel?] WARNING in posixtimer_send_sigqueue

[syzbot]

Hello,

syzbot tried to test the proposed patch but the build/boot failed:

security/apparmor/domain.c:695:3: error: expected expression
security/apparmor/domain.c:697:3: error: use of undeclared identifier 'new_profile'
security/apparmor/domain.c:699:8: error: use of undeclared identifier 'new_profile'
security/apparmor/domain.c:704:11: error: use of undeclared identifier 'new_profile'


Tested on:

commit:         744cf71b Add linux-next specific files for 20241115
git tree:       linux-next
kernel config:  https://syzkaller.appspot.com/x/.config?x=75175323f2078363
dashboard link: https://syzkaller.appspot.com/bug?extid=852e935b899bde73626e
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
patch:          https://syzkaller.appspot.com/x/patch.diff?x=17c582e8580000

Re: [syzbot] [kernel?] WARNING in posixtimer_send_sigqueue

[Frederic Weisbecker]

Le Fri, Nov 15, 2024 at 04:04:02AM -0800, syzbot a écrit :
> Hello,
> 
> syzbot tried to test the proposed patch but the build/boot failed:
> 
> security/apparmor/domain.c:695:3: error: expected expression
> security/apparmor/domain.c:697:3: error: use of undeclared identifier 'new_profile'
> security/apparmor/domain.c:699:8: error: use of undeclared identifier 'new_profile'
> security/apparmor/domain.c:704:11: error: use of undeclared identifier 'new_profile'
> 
> Tested on:
> 
> commit:         744cf71b Add linux-next specific files for 20241115
> git tree:       linux-next
> kernel config:  https://syzkaller.appspot.com/x/.config?x=75175323f2078363
> dashboard link: https://syzkaller.appspot.com/bug?extid=852e935b899bde73626e
> compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
> patch:          https://syzkaller.appspot.com/x/patch.diff?x=17c582e8580000
> 

Can you test on git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git
timers/core instead?

Re: [syzbot] [kernel?] WARNING in posixtimer_send_sigqueue

[Hillf Danton]

On Fri, 15 Nov 2024 21:55:02 +0100 Frederic Weisbecker <frederic@kernel.org>
> 
> Can you test on git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git
> timers/core instead?

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git  timers/core

--- x/kernel/signal.c
+++ y/kernel/signal.c
@@ -2003,9 +2003,15 @@ void posixtimer_send_sigqueue(struct k_i
 	if (!prepare_signal(sig, t, false)) {
 		result = TRACE_SIGNAL_IGNORED;
 
-		/* Paranoia check. Try to survive. */
-		if (WARN_ON_ONCE(!list_empty(&q->list)))
+		if (!list_empty(&q->list)) {
+			/*
+			 * If task group is exiting with the signal already pending,
+			 * wait for __exit_signal() to do its job. Otherwise if
+			 * ignored, it's not supposed to be queued. Try to survive.
+			 */
+			WARN_ON_ONCE(!(t->signal->flags & SIGNAL_GROUP_EXIT));
 			goto out;
+		}
 
 		/* Periodic timers with SIG_IGN are queued on the ignored list */
 		if (tmr->it_sig_periodic) {
--

Re: [syzbot] [kernel?] WARNING in posixtimer_send_sigqueue

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+852e935b899bde73626e@syzkaller.appspotmail.com
Tested-by: syzbot+852e935b899bde73626e@syzkaller.appspotmail.com

Tested on:

commit:         228ad72e Merge tag 'timers-v6.13-rc1' of https://git.l..
git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git timers/core
console output: https://syzkaller.appspot.com/x/log.txt?x=102f3cc0580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=a3e11aa0fc34acd5
dashboard link: https://syzkaller.appspot.com/bug?extid=852e935b899bde73626e
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
patch:          https://syzkaller.appspot.com/x/patch.diff?x=16b471a7980000

Note: testing is done by a robot and is best-effort only.