[PATCH 3.16.y-ckt 083/180] btrfs: don't accept bare namespace as a valid xattr

[Luis Henriques]

3.16.7-ckt11 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: David Sterba <dsterba at suse.cz>

commit 3c3b04d10ff1811a27f86684ccd2f5ba6983211d upstream.

Due to insufficient check in btrfs_is_valid_xattr, this unexpectedly
works:

 $ touch file
 $ setfattr -n user. -v 1 file
 $ getfattr -d file
user.="1"

ie. the missing attribute name after the namespace.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=94291
Reported-by: William Douglas <william.douglas at intel.com>
Signed-off-by: David Sterba <dsterba at suse.cz>
Signed-off-by: Chris Mason <clm at fb.com>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 fs/btrfs/xattr.c | 53 +++++++++++++++++++++++++++++++++++++++--------------
 1 file changed, 39 insertions(+), 14 deletions(-)

diff --git a/fs/btrfs/xattr.c b/fs/btrfs/xattr.c
index 7b29ee23b4ad..618e86ceede7 100644
--- a/fs/btrfs/xattr.c
+++ b/fs/btrfs/xattr.c
@@ -360,22 +360,42 @@ const struct xattr_handler *btrfs_xattr_handlers[] = {
 /*
  * Check if the attribute is in a supported namespace.
  *
- * This applied after the check for the synthetic attributes in the system
+ * This is applied after the check for the synthetic attributes in the system
  * namespace.
  */
-static bool btrfs_is_valid_xattr(const char *name)
+static int btrfs_is_valid_xattr(const char *name)
 {
-	return !strncmp(name, XATTR_SECURITY_PREFIX,
-			XATTR_SECURITY_PREFIX_LEN) ||
-	       !strncmp(name, XATTR_SYSTEM_PREFIX, XATTR_SYSTEM_PREFIX_LEN) ||
-	       !strncmp(name, XATTR_TRUSTED_PREFIX, XATTR_TRUSTED_PREFIX_LEN) ||
-	       !strncmp(name, XATTR_USER_PREFIX, XATTR_USER_PREFIX_LEN) ||
-		!strncmp(name, XATTR_BTRFS_PREFIX, XATTR_BTRFS_PREFIX_LEN);
+	int len = strlen(name);
+	int prefixlen = 0;
+
+	if (!strncmp(name, XATTR_SECURITY_PREFIX,
+			XATTR_SECURITY_PREFIX_LEN))
+		prefixlen = XATTR_SECURITY_PREFIX_LEN;
+	else if (!strncmp(name, XATTR_SYSTEM_PREFIX, XATTR_SYSTEM_PREFIX_LEN))
+		prefixlen = XATTR_SYSTEM_PREFIX_LEN;
+	else if (!strncmp(name, XATTR_TRUSTED_PREFIX, XATTR_TRUSTED_PREFIX_LEN))
+		prefixlen = XATTR_TRUSTED_PREFIX_LEN;
+	else if (!strncmp(name, XATTR_USER_PREFIX, XATTR_USER_PREFIX_LEN))
+		prefixlen = XATTR_USER_PREFIX_LEN;
+	else if (!strncmp(name, XATTR_BTRFS_PREFIX, XATTR_BTRFS_PREFIX_LEN))
+		prefixlen = XATTR_BTRFS_PREFIX_LEN;
+	else
+		return -EOPNOTSUPP;
+
+	/*
+	 * The name cannot consist of just prefix
+	 */
+	if (len <= prefixlen)
+		return -EINVAL;
+
+	return 0;
 }
 
 ssize_t btrfs_getxattr(struct dentry *dentry, const char *name,
 		       void *buffer, size_t size)
 {
+	int ret;
+
 	/*
 	 * If this is a request for a synthetic attribute in the system.*
 	 * namespace use the generic infrastructure to resolve a handler
@@ -384,8 +404,9 @@ ssize_t btrfs_getxattr(struct dentry *dentry, const char *name,
 	if (!strncmp(name, XATTR_SYSTEM_PREFIX, XATTR_SYSTEM_PREFIX_LEN))
 		return generic_getxattr(dentry, name, buffer, size);
 
-	if (!btrfs_is_valid_xattr(name))
-		return -EOPNOTSUPP;
+	ret = btrfs_is_valid_xattr(name);
+	if (ret)
+		return ret;
 	return __btrfs_getxattr(dentry->d_inode, name, buffer, size);
 }
 
@@ -393,6 +414,7 @@ int btrfs_setxattr(struct dentry *dentry, const char *name, const void *value,
 		   size_t size, int flags)
 {
 	struct btrfs_root *root = BTRFS_I(dentry->d_inode)->root;
+	int ret;
 
 	/*
 	 * The permission on security.* and system.* is not checked
@@ -409,8 +431,9 @@ int btrfs_setxattr(struct dentry *dentry, const char *name, const void *value,
 	if (!strncmp(name, XATTR_SYSTEM_PREFIX, XATTR_SYSTEM_PREFIX_LEN))
 		return generic_setxattr(dentry, name, value, size, flags);
 
-	if (!btrfs_is_valid_xattr(name))
-		return -EOPNOTSUPP;
+	ret = btrfs_is_valid_xattr(name);
+	if (ret)
+		return ret;
 
 	if (!strncmp(name, XATTR_BTRFS_PREFIX, XATTR_BTRFS_PREFIX_LEN))
 		return btrfs_set_prop(dentry->d_inode, name,
@@ -426,6 +449,7 @@ int btrfs_setxattr(struct dentry *dentry, const char *name, const void *value,
 int btrfs_removexattr(struct dentry *dentry, const char *name)
 {
 	struct btrfs_root *root = BTRFS_I(dentry->d_inode)->root;
+	int ret;
 
 	/*
 	 * The permission on security.* and system.* is not checked
@@ -442,8 +466,9 @@ int btrfs_removexattr(struct dentry *dentry, const char *name)
 	if (!strncmp(name, XATTR_SYSTEM_PREFIX, XATTR_SYSTEM_PREFIX_LEN))
 		return generic_removexattr(dentry, name);
 
-	if (!btrfs_is_valid_xattr(name))
-		return -EOPNOTSUPP;
+	ret = btrfs_is_valid_xattr(name);
+	if (ret)
+		return ret;
 
 	if (!strncmp(name, XATTR_BTRFS_PREFIX, XATTR_BTRFS_PREFIX_LEN))
 		return btrfs_set_prop(dentry->d_inode, name,