From: Wonhyuk Yang <vvghjk1234@xxxxxxxxx>
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@xxxxxxxxx
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Baik Song An <bsahn@xxxxxxxxxx>
Cc: Hong Yeon Kim <kimhy@xxxxxxxxxx>
Cc: Taeung Song <taeung@xxxxxxxxxxxxxxx>
Cc: linuxgeek@xxxxxxxxxxxx
Cc: stable@xxxxxxxxxxxxxxx
Fixes: 4909010788640 ("tracing: Add set_event_pid directory for future use")
Signed-off-by: Wonhyuk Yang <vvghjk1234@xxxxxxxxx>
Signed-off-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
---
kernel/trace/trace.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 498ae22d4ffa..4825883b2ffd 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -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;
}
--
2.35.1
