From 50c0e4215d888ae8e4fb06a752fd12bf00fa6b8e Mon Sep 17 00:00:00 2001 From: Goldwyn Rodrigues Date: Tue, 16 Aug 2022 16:42:56 -0500 Subject: [PATCH] btrfs: check if root is readonly while setting security xattr commit be3b6e9aea3ab36d952ff98c1a3f2211e411faba upstream. For a filesystem which has btrfs read-only property set to true, all write operations including xattr should be denied. However, security xattr can still be changed even if btrfs ro property is true. This happens because xattr_permission() does not have any restrictions on security.*, system.* and in some cases trusted.* from VFS and the decision is left to the underlying filesystem. See comments in xattr_permission() for more details. This patch checks if the root is read-only before performing the set xattr operation. Testcase: DEV=/dev/vdb MNT=/mnt mkfs.btrfs -f $DEV mount $DEV $MNT echo "file one" > $MNT/f1 setfattr -n "security.one" -v 2 $MNT/f1 btrfs property set /mnt ro true setfattr -n "security.one" -v 1 $MNT/f1 umount $MNT CC: stable@vger.kernel.org # 4.9+ Reviewed-by: Qu Wenruo Reviewed-by: Filipe Manana Signed-off-by: Goldwyn Rodrigues Reviewed-by: David Sterba Signed-off-by: David Sterba Signed-off-by: Greg Kroah-Hartman --- fs/btrfs/xattr.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/fs/btrfs/xattr.c b/fs/btrfs/xattr.c index 48858510739b2..cd7ddf24157a3 100644 --- a/fs/btrfs/xattr.c +++ b/fs/btrfs/xattr.c @@ -387,6 +387,9 @@ static int btrfs_xattr_handler_set(const struct xattr_handler *handler, const char *name, const void *buffer, size_t size, int flags) { + if (btrfs_root_readonly(BTRFS_I(inode)->root)) + return -EROFS; + name = xattr_full_name(handler, name); return btrfs_setxattr_trans(inode, name, buffer, size, flags); } -- 2.39.5