linux-hardening - [PATCH] string: Add additional __realloc

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Date: Wed,  1 May 2024 16:32:02 -0700
From: Kees Cook <keescook@...omium.org>
To: Andy Shevchenko <andy@...nel.org>
Cc: Kees Cook <keescook@...omium.org>,
	linux-hardening@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH] string: Add additional __realloc_size() annotations for "dup" helpers

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@...omium.org>
---
Cc: Andy Shevchenko <andy@...nel.org>
Cc: linux-hardening@...r.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