[PATCH 22/32] atags_proc: Use mem_to_flex_dup() with struct buffer

[Kees Cook]

As part of the work to perform bounds checking on all memcpy() uses,
replace the open-coded a deserialization of bytes out of memory into a
trailing flexible array by using a flex_array.h helper to perform the
allocation, bounds checking, and copying.

Cc: Russell King <li...@armlinux.org.uk>
Cc: Christian Brauner <brau...@kernel.org>
Cc: Andrew Morton <a...@linux-foundation.org>
Cc: Muchun Song <songmuc...@bytedance.com>
Cc: linux-arm-ker...@lists.infradead.org
Signed-off-by: Kees Cook <keesc...@chromium.org>
---
 arch/arm/kernel/atags_proc.c | 12 ++++--------
 1 file changed, 4 insertions(+), 8 deletions(-)

diff --git a/arch/arm/kernel/atags_proc.c b/arch/arm/kernel/atags_proc.c
index 3ec2afe78423..638bbb616daa 100644
--- a/arch/arm/kernel/atags_proc.c
+++ b/arch/arm/kernel/atags_proc.c
@@ -6,8 +6,8 @@
 #include <asm/page.h>
 
 struct buffer {
-       size_t size;
-       char data[];
+       DECLARE_FLEX_ARRAY_ELEMENTS_COUNT(size_t, size);
+       DECLARE_FLEX_ARRAY_ELEMENTS(char, data);
 };
 
 static ssize_t atags_read(struct file *file, char __user *buf,
@@ -38,7 +38,7 @@ static int __init init_atags_procfs(void)
         */
        struct proc_dir_entry *tags_entry;
        struct tag *tag = (struct tag *)atags_copy;
-       struct buffer *b;
+       struct buffer *b = NULL;
        size_t size;
 
        if (tag->hdr.tag != ATAG_CORE) {
@@ -54,13 +54,9 @@ static int __init init_atags_procfs(void)
 
        WARN_ON(tag->hdr.tag != ATAG_NONE);
 
-       b = kmalloc(sizeof(*b) + size, GFP_KERNEL);
-       if (!b)
+       if (mem_to_flex_dup(&b, atags_copy, size, GFP_KERNEL))
                goto nomem;
 
-       b->size = size;
-       memcpy(b->data, atags_copy, size);
-
        tags_entry = proc_create_data("atags", 0400, NULL, &atags_proc_ops, b);
        if (!tags_entry)
                goto nomem;
-- 
2.32.0