[bug report] bpf: Add pid filter support for uprobe_multi link

[bug report] bpf: Add pid filter support for uprobe_multi link

[Dan Carpenter]

Hello Jiri Olsa,

The patch b733eeade420: "bpf: Add pid filter support for uprobe_multi
link" from Aug 9, 2023 (linux-next), leads to the following Smatch
static checker warning:

	kernel/trace/bpf_trace.c:3227 bpf_uprobe_multi_link_attach()
	warn: missing error code here? 'get_pid_task()' failed. 'err' = '0'

kernel/trace/bpf_trace.c
    3217                 err = -EBADF;
    3218                 goto error_path_put;
    3219         }
    3220 
    3221         pid = attr->link_create.uprobe_multi.pid;
    3222         if (pid) {
    3223                 rcu_read_lock();
    3224                 task = get_pid_task(find_vpid(pid), PIDTYPE_PID);
    3225                 rcu_read_unlock();
    3226                 if (!task)
--> 3227                         goto error_path_put;

Should this have an error code?

    3228         }
    3229 
    3230         err = -ENOMEM;
    3231 

[ snip ]

    3288         err = bpf_link_prime(&link->link, &link_primer);
    3289         if (err)
    3290                 goto error_free;
    3291 
    3292         kvfree(ref_ctr_offsets);
    3293         return bpf_link_settle(&link_primer);
    3294 
    3295 error_free:
    3296         kvfree(ref_ctr_offsets);
    3297         kvfree(uprobes);
    3298         kfree(link);
    3299         if (task)
    3300                 put_task_struct(task);
    3301 error_path_put:
    3302         path_put(&path);
    3303         return err;
    3304 }

regards,
dan carpenter

Re: [bug report] bpf: Add pid filter support for uprobe_multi link

[Jiri Olsa]

On Fri, Sep 15, 2023 at 10:12:34AM +0300, Dan Carpenter wrote:
> Hello Jiri Olsa,
> 
> The patch b733eeade420: "bpf: Add pid filter support for uprobe_multi
> link" from Aug 9, 2023 (linux-next), leads to the following Smatch
> static checker warning:
> 
> 	kernel/trace/bpf_trace.c:3227 bpf_uprobe_multi_link_attach()
> 	warn: missing error code here? 'get_pid_task()' failed. 'err' = '0'
> 
> kernel/trace/bpf_trace.c
>     3217                 err = -EBADF;
>     3218                 goto error_path_put;
>     3219         }
>     3220 
>     3221         pid = attr->link_create.uprobe_multi.pid;
>     3222         if (pid) {
>     3223                 rcu_read_lock();
>     3224                 task = get_pid_task(find_vpid(pid), PIDTYPE_PID);
>     3225                 rcu_read_unlock();
>     3226                 if (!task)
> --> 3227                         goto error_path_put;
> 
> Should this have an error code?

yes, it should.. I'll send the fix below

thanks,
jirka


---
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index c1c1af63ced2..868008f56fec 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -3223,8 +3223,10 @@ int bpf_uprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr
 		rcu_read_lock();
 		task = get_pid_task(find_vpid(pid), PIDTYPE_PID);
 		rcu_read_unlock();
-		if (!task)
+		if (!task) {
+			err = -ESRCH;
 			goto error_path_put;
+		}
 	}
 
 	err = -ENOMEM;