[PATCH v2] tracing/probe: reject empty immediate strings

[Pengpeng Hou <pengpeng@iscas.ac.cn>]

parse_probe_arg() accepts quoted immediate strings and passes the body
after the opening quote to __parse_imm_string(). That helper currently
computes strlen(str) and immediately dereferences str[len - 1], which
underflows when the body is empty.

Reject empty immediate strings before checking for the closing quote.

Fixes: a42e3c4de964 ("tracing/probe: Add immediate string parameter support")
Signed-off-by: Pengpeng Hou <pengpeng@iscas.ac.cn>
---
Changes since v1:
- resend as a standalone patch instead of part of an accidental
  cross-subsystem 1/4 series

 kernel/trace/trace_probe.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
index e0a5dc86c07e..e1c73065dae5 100644
--- a/kernel/trace/trace_probe.c
+++ b/kernel/trace/trace_probe.c
@@ -1068,7 +1068,7 @@ static int __parse_imm_string(char *str, char **pbuf, int offs)
 {
 	size_t len = strlen(str);
 
-	if (str[len - 1] != '"') {
+	if (!len || str[len - 1] != '"') {
 		trace_probe_log_err(offs + len, IMMSTR_NO_CLOSE);
 		return -EINVAL;
 	}
-- 
2.50.1 (Apple Git-155)