linux-kernel - [PATCH v2] overflow.h: Add flex_array

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-ID: <20200609012233.GA3371@embeddedor>
Date:   Mon, 8 Jun 2020 20:22:33 -0500
From:   "Gustavo A. R. Silva" <gustavoars@...nel.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     linux-kernel@...r.kernel.org,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>
Subject: [PATCH v2] overflow.h: Add flex_array_size() helper

Add flex_array_size() helper for the calculation of the size, in bytes,
of a flexible array member contained within an enclosing structure.

Example of usage:

struct something {
	size_t count;
	struct foo items[];
};

struct something *instance;

instance = kmalloc(struct_size(instance, items, count), GFP_KERNEL);
instance->count = count;

memcpy(instance->items, source, flex_array_size(instance, items, instance->count));

The helper returns SIZE_MAX on overflow instead of wrapping around.

(Additionally replace parameter n with count in struct_size() for
unification).

Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
---
Changes in v2:
 - Add further information to the helper documentation.
 - Use same code style as struct_size() for consistency.

 include/linux/overflow.h | 25 +++++++++++++++++++++----
 1 file changed, 21 insertions(+), 4 deletions(-)

diff --git a/include/linux/overflow.h b/include/linux/overflow.h
index 659045046468f..d2329a914304c 100644
--- a/include/linux/overflow.h
+++ b/include/linux/overflow.h
@@ -304,16 +304,33 @@ static inline __must_check size_t __ab_c_size(size_t a, size_t b, size_t c)
  * struct_size() - Calculate size of structure with trailing array.
  * @p: Pointer to the structure.
  * @member: Name of the array member.
- * @n: Number of elements in the array.
+ * @count: Number of elements in the array.
  *
  * Calculates size of memory needed for structure @p followed by an
- * array of @n @member elements.
+ * array of @count @member elements.
  *
  * Return: number of bytes needed or SIZE_MAX on overflow.
  */
-#define struct_size(p, member, n)					\
-	__ab_c_size(n,							\
+#define struct_size(p, member, count)					\
+	__ab_c_size(count,							\
 		    sizeof(*(p)->member) + __must_be_array((p)->member),\
 		    sizeof(*(p)))
 
+/**
+ * flex_array_size() - Calculate size, in bytes, of a flexible array member
+ * within an enclosing structure. Read on for more details.
+ *
+ * @p: Pointer to the structure.
+ * @member: Name of the flexible array member.
+ * @count: Number of elements in the array.
+ *
+ * Calculates size, in bytes, of a flexible array @member of @count elements
+ * within structure @p.
+ *
+ * Return: number of bytes needed or SIZE_MAX on overflow.
+ */
+#define flex_array_size(p, member, count)					\
+	array_size(count,							\
+		    sizeof(*(p)->member) + __must_be_array((p)->member))
+
 #endif /* __LINUX_OVERFLOW_H */
-- 
2.27.0