Re: [PATCH] tracing/kprobe: Fix NULL pointer access in trace_porbe_unlink()

[Steven Rostedt <rostedt@goodmis.org>]

On Tue, 17 Sep 2019 14:11:37 +0900
Masami Hiramatsu <mhiramat@kernel.org> wrote:

> Fix NULL pointer access in trace_probe_unlink() by initializing
> trace_probe.list correctly in trace_probe_init().
> 
> In the error case of trace_probe_init(), it can call trace_probe_unlink()
> before initializing trace_probe.list member. This causes NULL pointer
> dereference at list_del_init() in trace_probe_unlink().
> 
> Syzbot reported :
> 
> kasan: CONFIG_KASAN_INLINE enabled
> kasan: GPF could be caused by NULL-ptr deref or user memory access
> general protection fault: 0000 [#1] PREEMPT SMP KASAN
> CPU: 1 PID: 8633 Comm: syz-executor797 Not tainted 5.3.0-rc8-next-20190915
> #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> RIP: 0010:__list_del_entry_valid+0x85/0xf5 lib/list_debug.c:51
> Code: 0f 84 e1 00 00 00 48 b8 22 01 00 00 00 00 ad de 49 39 c4 0f 84 e2 00
> 00 00 48 b8 00 00 00 00 00 fc ff df 4c 89 e2 48 c1 ea 03 <80> 3c 02 00 75
> 53 49 8b 14 24 4c 39 f2 0f 85 99 00 00 00 49 8d 7d
> RSP: 0018:ffff888090a7f9d8 EFLAGS: 00010246
> RAX: dffffc0000000000 RBX: ffff88809b6f90c0 RCX: ffffffff817c0ca9
> RDX: 0000000000000000 RSI: ffffffff817c0a73 RDI: ffff88809b6f90c8
> RBP: ffff888090a7f9f0 R08: ffff88809a04e600 R09: ffffed1015d26aed
> R10: ffffed1015d26aec R11: ffff8880ae935763 R12: 0000000000000000
> R13: 0000000000000000 R14: ffff88809b6f90c0 R15: ffff88809b6f90d0
> FS:  0000555556f99880(0000) GS:ffff8880ae900000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00000000006cc090 CR3: 00000000962b2000 CR4: 00000000001406e0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>   __list_del_entry include/linux/list.h:131 [inline]
>   list_del_init include/linux/list.h:190 [inline]
>   trace_probe_unlink+0x1f/0x200 kernel/trace/trace_probe.c:959
>   trace_probe_cleanup+0xd3/0x110 kernel/trace/trace_probe.c:973
>   trace_probe_init+0x3f2/0x510 kernel/trace/trace_probe.c:1011
>   alloc_trace_uprobe+0x5e/0x250 kernel/trace/trace_uprobe.c:353
>   create_local_trace_uprobe+0x109/0x4a0 kernel/trace/trace_uprobe.c:1508
>   perf_uprobe_init+0x131/0x210 kernel/trace/trace_event_perf.c:314
>   perf_uprobe_event_init+0x106/0x1a0 kernel/events/core.c:8898
>   perf_try_init_event+0x135/0x590 kernel/events/core.c:10184
>   perf_init_event kernel/events/core.c:10228 [inline]
>   perf_event_alloc.part.0+0x1b89/0x33d0 kernel/events/core.c:10505
>   perf_event_alloc kernel/events/core.c:10887 [inline]
>   __do_sys_perf_event_open+0xa2d/0x2d00 kernel/events/core.c:10989
>   __se_sys_perf_event_open kernel/events/core.c:10871 [inline]
>   __x64_sys_perf_event_open+0xbe/0x150 kernel/events/core.c:10871
>   do_syscall_64+0xfa/0x760 arch/x86/entry/common.c:290
>   entry_SYSCALL_64_after_hwframe+0x49/0xbe
> 
> Reported-by: syzbot+2f807f4d3a2a4e87f18f@syzkaller.appspotmail.com
> Fixes: ca89bc071d5e ("tracing/kprobe: Add multi-probe per event support")
> Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>

Thanks Masami. I was just about to get my pull request to Linus out,
but will now add this and start running my tests with it.

-- Steve


> ---
>  kernel/trace/trace_probe.c |   11 ++++++-----
>  1 file changed, 6 insertions(+), 5 deletions(-)
> 
> diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
> index 1e67fef06e53..baf58a3612c0 100644
> --- a/kernel/trace/trace_probe.c
> +++ b/kernel/trace/trace_probe.c
> @@ -986,6 +986,12 @@ int trace_probe_init(struct trace_probe *tp, const char *event,
>  	if (!tp->event)
>  		return -ENOMEM;
>  
> +	INIT_LIST_HEAD(&tp->event->files);
> +	INIT_LIST_HEAD(&tp->event->class.fields);
> +	INIT_LIST_HEAD(&tp->event->probes);
> +	INIT_LIST_HEAD(&tp->list);
> +	list_add(&tp->event->probes, &tp->list);
> +
>  	call = trace_probe_event_call(tp);
>  	call->class = &tp->event->class;
>  	call->name = kstrdup(event, GFP_KERNEL);
> @@ -999,11 +1005,6 @@ int trace_probe_init(struct trace_probe *tp, const char *event,
>  		ret = -ENOMEM;
>  		goto error;
>  	}
> -	INIT_LIST_HEAD(&tp->event->files);
> -	INIT_LIST_HEAD(&tp->event->class.fields);
> -	INIT_LIST_HEAD(&tp->event->probes);
> -	INIT_LIST_HEAD(&tp->list);
> -	list_add(&tp->event->probes, &tp->list);
>  
>  	return 0;
>