netdev - [PATCH 3/3] btrfs: tree-checker: Avoid accidental stack VLA

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Message-Id: <1520479847-39174-4-git-send-email-keescook@chromium.org>
Date:   Wed,  7 Mar 2018 19:30:47 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Kees Cook <keescook@...omium.org>, linux-kernel@...r.kernel.org,
        corbet@....net, gustavo@...eddedor.com, rostedt@...dmis.org,
        Chris Mason <clm@...com>, Josef Bacik <jbacik@...com>,
        David Sterba <dsterba@...e.com>,
        "David S. Miller" <davem@...emloft.net>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Borislav Petkov <bp@...e.de>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Ian Abbott <abbotti@....co.uk>,
        "Tobin C. Harding" <me@...in.cc>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Petr Mladek <pmladek@...e.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Pantelis Antoniou <pantelis.antoniou@...sulko.com>,
        linux-btrfs@...r.kernel.org, netdev@...r.kernel.org,
        kernel-hardening@...ts.openwall.com
Subject: [PATCH 3/3] btrfs: tree-checker: Avoid accidental stack VLA

In the quest to remove all stack VLAs from the kernel[1], this refactors
the stack array size calculation to avoid using max(), which makes the
compiler think the size isn't fixed.

[1] https://lkml.org/lkml/2018/3/7/621

Signed-off-by: Kees Cook <keescook@...omium.org>
---
 fs/btrfs/tree-checker.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/btrfs/tree-checker.c b/fs/btrfs/tree-checker.c
index c3c8d48f6618..59bd07694118 100644
--- a/fs/btrfs/tree-checker.c
+++ b/fs/btrfs/tree-checker.c
@@ -341,7 +341,8 @@ static int check_dir_item(struct btrfs_root *root,
 		 */
 		if (key->type == BTRFS_DIR_ITEM_KEY ||
 		    key->type == BTRFS_XATTR_ITEM_KEY) {
-			char namebuf[max(BTRFS_NAME_LEN, XATTR_NAME_MAX)];
+			char namebuf[SIMPLE_MAX(BTRFS_NAME_LEN,
+						XATTR_NAME_MAX)];
 
 			read_extent_buffer(leaf, namebuf,
 					(unsigned long)(di + 1), name_len);
-- 
2.7.4