linux-hardening - [PATCH] overflow: improve size

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Message-ID: <ebdae636-11f3-4f02-a158-f15bbed2847f@stanley.mountain>
Date: Mon, 18 Nov 2024 09:09:28 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: Kees Cook <kees@...nel.org>
Cc: "Gustavo A. R. Silva" <gustavoars@...nel.org>,
	linux-hardening@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] overflow: improve size_add/mul for 32bit systems

On 32bit systems, if you pass a long long to size_add()/mul() the top
32 bits are truncated away so the function doesn't work as expected.
Add a test to prevent this.

Signed-off-by: Dan Carpenter <dan.carpenter@...aro.org>
---
 include/linux/overflow.h | 28 ++++++++++++++++++++++++++--
 1 file changed, 26 insertions(+), 2 deletions(-)

diff --git a/include/linux/overflow.h b/include/linux/overflow.h
index 0c7e3dcfe867..e90cd5245497 100644
--- a/include/linux/overflow.h
+++ b/include/linux/overflow.h
@@ -263,7 +263,7 @@ static inline bool __must_check __must_check_overflow(bool overflow)
  * with any overflow causing the return value to be SIZE_MAX. The
  * lvalue must be size_t to avoid implicit type conversion.
  */
-static inline size_t __must_check size_mul(size_t factor1, size_t factor2)
+static inline size_t __must_check __size_mul(size_t factor1, size_t factor2)
 {
 	size_t bytes;
 
@@ -273,6 +273,18 @@ static inline size_t __must_check size_mul(size_t factor1, size_t factor2)
 	return bytes;
 }
 
+#define size_mul(a, b) ({						\
+	typeof(a) __a = (a);						\
+	typeof(b) __b = (b);						\
+	unsigned long __res;						\
+	if (UINT_MAX == SIZE_MAX &&					\
+	    (__a >= (u64)SIZE_MAX || __b >= (u64)SIZE_MAX))		\
+		__res = ULONG_MAX;					\
+	else								\
+		__res = __size_mul(__a, __b);				\
+	__res;								\
+})
+
 /**
  * size_add() - Calculate size_t addition with saturation at SIZE_MAX
  * @addend1: first addend
@@ -282,7 +294,7 @@ static inline size_t __must_check size_mul(size_t factor1, size_t factor2)
  * with any overflow causing the return value to be SIZE_MAX. The
  * lvalue must be size_t to avoid implicit type conversion.
  */
-static inline size_t __must_check size_add(size_t addend1, size_t addend2)
+static inline size_t __must_check __size_add(size_t addend1, size_t addend2)
 {
 	size_t bytes;
 
@@ -292,6 +304,18 @@ static inline size_t __must_check size_add(size_t addend1, size_t addend2)
 	return bytes;
 }
 
+#define size_add(a, b) ({						\
+	typeof(a) __a = (a);						\
+	typeof(b) __b = (b);						\
+	unsigned long __res;						\
+	if (UINT_MAX == SIZE_MAX &&					\
+	    (__a >= (u64)SIZE_MAX || __b >= (u64)SIZE_MAX))		\
+		__res = ULONG_MAX;					\
+	else								\
+		__res = __size_add(__a, __b);				\
+	__res;								\
+})
+
 /**
  * size_sub() - Calculate size_t subtraction with saturation at SIZE_MAX
  * @minuend: value to subtract from
-- 
2.45.2