linux-kernel - [PATCH] aio: Prefer struct_size over open coded arithmetic

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Message-Id: <20210919094539.30589-1-len.baker@gmx.com>
Date:   Sun, 19 Sep 2021 11:45:39 +0200
From:   Len Baker <len.baker@....com>
To:     Benjamin LaHaise <bcrl@...ck.org>,
        Alexander Viro <viro@...iv.linux.org.uk>
Cc:     Len Baker <len.baker@....com>, Kees Cook <keescook@...omium.org>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>, linux-aio@...ck.org,
        linux-fsdevel@...r.kernel.org, linux-hardening@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] aio: 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/aio.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/fs/aio.c b/fs/aio.c
index 51b08ab01dff..c2978c0b872c 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -659,8 +659,7 @@ static int ioctx_add_table(struct kioctx *ctx, struct mm_struct *mm)
 		new_nr = (table ? table->nr : 1) * 4;
 		spin_unlock(&mm->ioctx_lock);

-		table = kzalloc(sizeof(*table) + sizeof(struct kioctx *) *
-				new_nr, GFP_KERNEL);
+		table = kzalloc(struct_size(table, table, new_nr), GFP_KERNEL);
 		if (!table)
 			return -ENOMEM;

--
2.25.1