[PATCH 5.16 0754/1017] gcc-plugins/stackleak: Exactly match strings instead of prefixes

Greg Kroah-Hartman
2022-04-05T13:24:20Z

From: Kees Cook <keescook@chromium.org>

[ Upstream commit 27e9faf415dbf94af19b9c827842435edbc1fbbc ]

Since STRING_CST may not be NUL terminated, strncmp() was used for check
for equality. However, this may lead to mismatches for longer section
names where the start matches the tested-for string. Test for exact
equality by checking for the presences of NUL termination.

Cc: Alexander Popov <alex.popov@linux.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
scripts/gcc-plugins/stackleak_plugin.c | 25 +++++++++++++++++++++----
1 file changed, 21 insertions(+), 4 deletions(-)

diff --git a/scripts/gcc-plugins/stackleak_plugin.c b/scripts/gcc-plugins/stackleak_plugin.c
index e9db7dcb3e5f..b04aa8e91a41 100644
--- a/scripts/gcc-plugins/stackleak_plugin.c
+++ b/scripts/gcc-plugins/stackleak_plugin.c
@@ -429,6 +429,23 @@ static unsigned int stackleak_cleanup_execute(void)
return 0;
}

+/*
+ * STRING_CST may or may not be NUL terminated:
+ * https://gcc.gnu.org/onlinedocs/gccint/Constant-expressions.html
+ */
+static inline bool string_equal(tree node, const char *string, int length)
+{
+ if (TREE_STRING_LENGTH(node) < length)
+ return false;
+ if (TREE_STRING_LENGTH(node) > length + 1)
+ return false;
+ if (TREE_STRING_LENGTH(node) == length + 1 &&
+ TREE_STRING_POINTER(node)[length] != '\0')
+ return false;
+ return !memcmp(TREE_STRING_POINTER(node), string, length);
+}
+#define STRING_EQUAL(node, str) string_equal(node, str, strlen(str))
+
static bool stackleak_gate(void)
{
tree section;
@@ -438,13 +455,13 @@ static bool stackleak_gate(void)
if (section && TREE_VALUE(section)) {
section = TREE_VALUE(TREE_VALUE(section));

- if (!strncmp(TREE_STRING_POINTER(section), ".init.text", 10))
+ if (STRING_EQUAL(section, ".init.text"))
return false;
- if (!strncmp(TREE_STRING_POINTER(section), ".devinit.text", 13))
+ if (STRING_EQUAL(section, ".devinit.text"))
return false;
- if (!strncmp(TREE_STRING_POINTER(section), ".cpuinit.text", 13))
+ if (STRING_EQUAL(section, ".cpuinit.text"))
return false;
- if (!strncmp(TREE_STRING_POINTER(section), ".meminit.text", 13))
+ if (STRING_EQUAL(section, ".meminit.text"))
return false;
}

--
2.34.1