linux-hardening - [PATCH] afs: Prefer struct_size over open coded arithmetic

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Message-Id: <20210919094432.30510-1-len.baker@gmx.com>
Date:   Sun, 19 Sep 2021 11:44:32 +0200
From:   Len Baker <len.baker@....com>
To:     David Howells <dhowells@...hat.com>,
        Marc Dionne <marc.dionne@...istor.com>
Cc:     Len Baker <len.baker@....com>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        linux-afs@...ts.infradead.org, linux-hardening@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] afs: Prefer struct_size over open coded arithmetic

As noted in the "Deprecated Interfaces, Language Features, Attributes,
and Conventions" documentation [1], size calculations (especially
multiplication) should not be performed in memory allocator (or similar)
function arguments due to the risk of them overflowing. This could lead
to values wrapping around and a smaller allocation being made than the
caller was expecting. Using those allocations could lead to linear
overflows of heap memory and other misbehaviors.

So, use the struct_size() helper to do the arithmetic instead of the
argument "size + size * count" in the kzalloc() function.

[1] https://www.kernel.org/doc/html/latest/process/deprecated.html#open-coded-arithmetic-in-allocator-arguments

Signed-off-by: Len Baker <len.baker@....com>
---
 fs/afs/security.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/fs/afs/security.c b/fs/afs/security.c
index 3c7a8fc4f93f..7c6a63a30394 100644
--- a/fs/afs/security.c
+++ b/fs/afs/security.c
@@ -219,8 +219,7 @@ void afs_cache_permit(struct afs_vnode *vnode, struct key *key,
 	 * yet.
 	 */
 	size++;
-	new = kzalloc(sizeof(struct afs_permits) +
-		      sizeof(struct afs_permit) * size, GFP_NOFS);
+	new = kzalloc(struct_size(new, permits, size), GFP_NOFS);
 	if (!new)
 		goto out_put;

--
2.25.1