Re: [PATCH] tracing: Fix missing errno when zero parser->idx in trace_pid_write

[Pu Lehui <pulehui@huawei.com>]

On 2025/8/21 15:17, Pu Lehui wrote:
> From: Pu Lehui <pulehui@huawei.com>
> 
> When trace_get_user in trace_pid_write parses an only space, the
> !trace_parser_loaded branch will break with no errno, causing
> tr->filtered_pids to still be assigned with pid_list, which may trigger
> potential problems.

Hi Steven,

Sorry, this patch will break the cleanup functionality of 
"set_ftrace_pid" as indicated in [0]. Pls ignore this patch.

Link: https://lore.kernel.org/all/202509022339.ae20a8bb-lkp@intel.com [0]

> 
> This patch will also silence the fault injection syzkaller warning in
> tracepoint_add_func [0]. We can reproduce the warning by following the
> steps below:
> 1. echo 8 >> set_event_notrace_pid. Let tr->filtered_pids owns one pid
>     and register sched_switch tracepoint.
> 2. echo ' ' >> set_event_pid, and perform fault injection during chunk
>     allocation of trace_pid_list_alloc. Let pid_list with no pid and
> assign to tr->filtered_pids.
> 3. echo ' ' >> set_event_pid. Let pid_list is NULL and assign to
>     tr->filtered_pids.
> 4. echo 9 >> set_event_pid, will trigger the double register
>     sched_switch tracepoint warning.

As for this fault injection syzkaller issue, shall we need to silence 
it? How about the below fix?

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index e6b50b416e63..c17c031e7917 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -834,7 +834,11 @@ int trace_pid_write(struct trace_pid_list 
*filtered_pids,
                 /* copy the current bits to the new max */
                 ret = trace_pid_list_first(filtered_pids, &pid);
                 while (!ret) {
-                       trace_pid_list_set(pid_list, pid);
+                       ret = trace_pid_list_set(pid_list, pid);
+                       if (ret) {
+                               trace_parser_put(&parser);
+                               return ret;
+                       }
                         ret = trace_pid_list_next(filtered_pids, pid + 
1, &pid);
                         nr_pids++;
                 }

> 
> Link: https://lore.kernel.org/all/67cb890e.050a0220.d8275.022e.GAE@google.com [0]
> Fixes: b27f266f74fb ("tracing: Fix return value of trace_pid_write()")
> Signed-off-by: Pu Lehui <pulehui@huawei.com>
> ---
>   kernel/trace/trace.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 8d8935ed416d..feeb7eb71318 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -853,10 +853,10 @@ int trace_pid_write(struct trace_pid_list *filtered_pids,
>   		ubuf += ret;
>   		cnt -= ret;
>   
> +		ret = -EINVAL;
>   		if (!trace_parser_loaded(&parser))
>   			break;
>   
> -		ret = -EINVAL;
>   		if (kstrtoul(parser.buffer, 0, &val))
>   			break;
>