From: Wonhyuk Yang vvghjk1234@gmail.com

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 --- 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; }