Commit b27f266f authored by Wonhyuk Yang's avatar Wonhyuk Yang Committed by Steven Rostedt (Google)
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tracing: Fix return value of trace_pid_write() 

Setting set_event_pid with trailing whitespace lead to endless write
system calls like below.

    $ strace echo "123 " > /sys/kernel/debug/tracing/set_event_pid
    execve("/usr/bin/echo", ["echo", "123 "], ...) = 0
    ...
    write(1, "123 \n", 5)                   = 4
    write(1, "\n", 1)                       = 0
    write(1, "\n", 1)                       = 0
    write(1, "\n", 1)                       = 0
    write(1, "\n", 1)                       = 0
    write(1, "\n", 1)                       = 0
    ....

This is because, the result of trace_get_user's are not returned when it
read at least one pid. To fix it, update read variable even if
parser->idx == 0.

The result of applied patch is below.

    $ strace echo "123 " > /sys/kernel/debug/tracing/set_event_pid
    execve("/usr/bin/echo", ["echo", "123 "], ...) = 0
    ...
    write(1, "123 \n", 5)                   = 5
    close(1)                                = 0

Link: https://lkml.kernel.org/r/20220503050546.288911-1-vvghjk1234@gmail.com



Cc: Ingo Molnar <mingo@redhat.com>
Cc: Baik Song An <bsahn@etri.re.kr>
Cc: Hong Yeon Kim <kimhy@etri.re.kr>
Cc: Taeung Song <taeung@reallinux.co.kr>
Cc: linuxgeek@linuxgeek.io
Cc: stable@vger.kernel.org
Fixes: 49090107 ("tracing: Add set_event_pid directory for future use")
Signed-off-by: default avatarWonhyuk Yang <vvghjk1234@gmail.com>
Signed-off-by: default avatarSteven Rostedt (Google) <rostedt@goodmis.org>
parent 99696a25

kernel/trace/trace.c

+4 −2
Original line number Diff line number Diff line
@@ -721,13 +721,16 @@ int trace_pid_write(struct trace_pid_list *filtered_pids, 
		pos = 0;



		ret = trace_get_user(&parser, ubuf, cnt, &pos);

		if (ret < 0 || !trace_parser_loaded(&parser))

		if (ret < 0)

			break;



		read += ret;

		ubuf += ret;

		cnt -= ret;



		if (!trace_parser_loaded(&parser))

			break;



		ret = -EINVAL;

		if (kstrtoul(parser.buffer, 0, &val))

			break;
@@ -753,7 +756,6 @@ int trace_pid_write(struct trace_pid_list *filtered_pids, 
	if (!nr_pids) {

		/* Cleared the list of pids */

		trace_pid_list_free(pid_list);

		read = ret;

		pid_list = NULL;

	}