linux-kernel - [PATCH 5.11 293/342] security: commoncap: fix -Wstringop-overread warning

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Date:   Mon, 10 May 2021 12:21:23 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
        Christian Brauner <christian.brauner@...ntu.com>,
        James Morris <jamorris@...ux.microsoft.com>,
        Andrey Zhizhikin <andrey.z@...il.com>
Subject: [PATCH 5.11 293/342] security: commoncap: fix -Wstringop-overread warning

From: Arnd Bergmann <arnd@...db.de>

commit 82e5d8cc768b0c7b03c551a9ab1f8f3f68d5f83f upstream.

gcc-11 introdces a harmless warning for cap_inode_getsecurity:

security/commoncap.c: In function ‘cap_inode_getsecurity’:
security/commoncap.c:440:33: error: ‘memcpy’ reading 16 bytes from a region of size 0 [-Werror=stringop-overread]
  440 |                                 memcpy(&nscap->data, &cap->data, sizeof(__le32) * 2 * VFS_CAP_U32);
      |                                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The problem here is that tmpbuf is initialized to NULL, so gcc assumes
it is not accessible unless it gets set by vfs_getxattr_alloc().  This is
a legitimate warning as far as I can tell, but the code is correct since
it correctly handles the error when that function fails.

Add a separate NULL check to tell gcc about it as well.

Signed-off-by: Arnd Bergmann <arnd@...db.de>
Acked-by: Christian Brauner <christian.brauner@...ntu.com>
Signed-off-by: James Morris <jamorris@...ux.microsoft.com>
Cc: Andrey Zhizhikin <andrey.z@...il.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 security/commoncap.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/security/commoncap.c
+++ b/security/commoncap.c
@@ -391,7 +391,7 @@ int cap_inode_getsecurity(struct inode *
 				 &tmpbuf, size, GFP_NOFS);
 	dput(dentry);
 
-	if (ret < 0)
+	if (ret < 0 || !tmpbuf)
 		return ret;
 
 	fs_ns = inode->i_sb->s_user_ns;