[PATCH 5.18 751/879] tracing: Fix return value of trace_pid_write()

Greg Kroah-Hartman
2022-06-08T01:03:38Z

From: Wonhyuk Yang <vvghjk1234@gmail.com>

commit b27f266f74fbda4ee36c2b2b04d15992860cf23b upstream.

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: 4909010788640 ("tracing: Add set_event_pid directory for future use")
Signed-off-by: Wonhyuk Yang <vvghjk1234@gmail.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
kernel/trace/trace.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -721,13 +721,16 @@ int trace_pid_write(struct trace_pid_lis
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_lis
if (!nr_pids) {
/* Cleared the list of pids */
trace_pid_list_free(pid_list);
- read = ret;
pid_list = NULL;
}