[PATCH] string: Add additional __realloc_size() annotations for "dup" helpers

Kees Cook
2024-05-01T23:32:05Z

Several other "dup"-style interfaces could use the __realloc_size()
attribute. (As a reminder to myself and others: "realloc" is used here
instead of "alloc" because the "alloc_size" attribute implies that the
memory contents are uninitialized. Since we're copying contents into the
resulting allocation, it must use "realloc_size" to avoid confusing the
compiler's optimization passes.)

Add KUnit test coverage where possible. (KUnit still does not have the
ability to manipulate userspace memory.)

Signed-off-by: Kees Cook <keescook@chromium.org>
---
Cc: Andy Shevchenko <andy@kernel.org>
Cc: linux-hardening@vger.kernel.org
---
include/linux/string.h | 13 ++++++++-----
lib/fortify_kunit.c | 26 ++++++++++++++++++++++++++
2 files changed, 34 insertions(+), 5 deletions(-)

diff --git a/include/linux/string.h b/include/linux/string.h
index 86aa6cd35167..10e5177bb49c 100644
--- a/include/linux/string.h
+++ b/include/linux/string.h
@@ -14,8 +14,8 @@
#include <uapi/linux/string.h>

extern char *strndup_user(const char __user *, long);
-extern void *memdup_user(const void __user *, size_t);
-extern void *vmemdup_user(const void __user *, size_t);
+extern void *memdup_user(const void __user *, size_t) __realloc_size(2);
+extern void *vmemdup_user(const void __user *, size_t) __realloc_size(2);
extern void *memdup_user_nul(const void __user *, size_t);

/**
@@ -27,7 +27,8 @@ extern void *memdup_user_nul(const void __user *, size_t);
* Return: an ERR_PTR() on failure. Result is physically
* contiguous, to be freed by kfree().
*/
-static inline void *memdup_array_user(const void __user *src, size_t n, size_t size)
+static inline __realloc_size(2, 3)
+void *memdup_array_user(const void __user *src, size_t n, size_t size)
{
size_t nbytes;

@@ -46,7 +47,8 @@ static inline void *memdup_array_user(const void __user *src, size_t n, size_t s
* Return: an ERR_PTR() on failure. Result may be not
* physically contiguous. Use kvfree() to free.
*/
-static inline void *vmemdup_array_user(const void __user *src, size_t n, size_t size)
+static inline __realloc_size(2, 3)
+void *vmemdup_array_user(const void __user *src, size_t n, size_t size)
{
size_t nbytes;

@@ -285,7 +287,8 @@ extern char *kstrndup(const char *s, size_t len, gfp_t gfp);
extern void *kmemdup(const void *src, size_t len, gfp_t gfp) __realloc_size(2);
extern void *kvmemdup(const void *src, size_t len, gfp_t gfp) __realloc_size(2);
extern char *kmemdup_nul(const char *s, size_t len, gfp_t gfp);
-extern void *kmemdup_array(const void *src, size_t element_size, size_t count, gfp_t gfp);
+extern void *kmemdup_array(const void *src, size_t element_size, size_t count, gfp_t gfp)
+ __realloc_size(2, 3);

/* lib/argv_split.c */
extern char **argv_split(gfp_t gfp, const char *str, int *argcp);
diff --git a/lib/fortify_kunit.c b/lib/fortify_kunit.c
index 306522fd0aa2..87b873108350 100644
--- a/lib/fortify_kunit.c
+++ b/lib/fortify_kunit.c
@@ -363,6 +363,31 @@ DEFINE_ALLOC_SIZE_TEST_PAIR(kvmalloc)
} while (0)
DEFINE_ALLOC_SIZE_TEST_PAIR(devm_kmalloc)

+static const char * const test_phrases[] = {
+ "",
+ "Hello there",
+ "A longer string, just for variety",
+};
+
+#define TEST_realloc(checker) do { \
+ gfp_t gfp = GFP_KERNEL; \
+ size_t len; \
+ int idx; \
+ \
+ for (idx = 0; idx < ARRAY_SIZE(test_phrases); idx++) { \
+ len = strlen(test_phrases[idx]); \
+ KUNIT_EXPECT_EQ(test, __builtin_constant_p(len), 0); \
+ checker(len, kmemdup_array(test_phrases[idx], len, 1, \
+ gfp), kfree(p)); \
+ checker(len, kmemdup(test_phrases[idx], len, gfp), \
+ kfree(p)); \
+ } \
+} while (0)
+static void fortify_test_realloc_size(struct kunit *test)
+{
+ TEST_realloc(check_dynamic);
+}
+
/*
* We can't have an array at the end of a structure or else
* builds without -fstrict-flex-arrays=3 will report them as
@@ -1046,6 +1071,7 @@ static struct kunit_case fortify_test_cases[] = {
KUNIT_CASE(fortify_test_alloc_size_kvmalloc_dynamic),
KUNIT_CASE(fortify_test_alloc_size_devm_kmalloc_const),
KUNIT_CASE(fortify_test_alloc_size_devm_kmalloc_dynamic),
+ KUNIT_CASE(fortify_test_realloc_size),
KUNIT_CASE(fortify_test_strlen),
KUNIT_CASE(fortify_test_strnlen),
KUNIT_CASE(fortify_test_strcpy),
--
2.34.1