From 5ef2cd36ebdd865743bf97e53d564916c668859f Mon Sep 17 00:00:00 2001 From: Wonhyuk Yang Date: Tue, 3 May 2022 14:05:46 +0900 Subject: [PATCH] tracing: Fix return value of trace_pid_write() [ Upstream commit b27f266f74fbda4ee36c2b2b04d15992860cf23b ] 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 Cc: Baik Song An Cc: Hong Yeon Kim Cc: Taeung Song 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 Signed-off-by: Steven Rostedt (Google) Signed-off-by: Sasha Levin --- 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 abbe8489faae..d93f9c59f50e 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -711,13 +711,16 @@ 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; @@ -743,7 +746,6 @@ 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; }