linux-hardening - [PATCH] exec: Fix min/max typo in stack space calculation

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Message-Id: <20220201190700.3147041-1-keescook@chromium.org>
Date:   Tue,  1 Feb 2022 11:07:00 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Kees Cook <keescook@...omium.org>,
        Ariadne Conill <ariadne@...eferenced.org>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Matthew Wilcox <willy@...radead.org>,
        Christian Brauner <brauner@...nel.org>,
        Rich Felker <dalias@...c.org>,
        Eric Biederman <ebiederm@...ssion.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: [PATCH] exec: Fix min/max typo in stack space calculation

When handling the argc == 0 case, the stack space calculation should be
using max() not min().

Signed-off-by: Kees Cook <keescook@...omium.org>
---
This is a fix for exec-force-single-empty-string-when-argv-is-empty.patch
https://lore.kernel.org/mm-commits/20220201004100.BF6D6C340E8@smtp.kernel.org/
---
 fs/exec.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/exec.c b/fs/exec.c
index bbf3aadf7ce1..40b1008fb0f7 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -502,7 +502,7 @@ static int bprm_stack_limits(struct linux_binprm *bprm)
 	 * argc can never be 0, to keep them from walking envp by accident.
 	 * See do_execveat_common().
 	 */
-	ptr_size = (min(bprm->argc, 1) + bprm->envc) * sizeof(void *);
+	ptr_size = (max(bprm->argc, 1) + bprm->envc) * sizeof(void *);
 	if (limit <= ptr_size)
 		return -E2BIG;
 	limit -= ptr_size;
-- 
2.30.2