vfs: create a generic checking function for FS_IOC_FSSETXATTR

Create a generic checking function for the incoming FS_IOC_FSSETXATTR
fsxattr values so that we can standardize some of the implementation
behaviors.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Jan Kara <jack@suse.cz>

1 files changed, 23 insertions, 0 deletions

diff --git a/fs/inode.c b/fs/inode.c
index 8072a09fd0b9..ba2bafa22885 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -2194,3 +2194,26 @@ int vfs_ioc_setflags_prepare(struct inode *inode, unsigned int oldflags,
 	return 0;
 }
 EXPORT_SYMBOL(vfs_ioc_setflags_prepare);
+
+/*
+ * Generic function to check FS_IOC_FSSETXATTR values and reject any invalid
+ * configurations.
+ *
+ * Note: the caller should be holding i_mutex, or else be sure that they have
+ * exclusive access to the inode structure.
+ */
+int vfs_ioc_fssetxattr_check(struct inode *inode, const struct fsxattr *old_fa,
+			     struct fsxattr *fa)
+{
+	/*
+	 * Can't modify an immutable/append-only file unless we have
+	 * appropriate permission.
+	 */
+	if ((old_fa->fsx_xflags ^ fa->fsx_xflags) &
+			(FS_XFLAG_IMMUTABLE | FS_XFLAG_APPEND) &&
+	    !capable(CAP_LINUX_IMMUTABLE))
+		return -EPERM;
+
+	return 0;
+}
+EXPORT_SYMBOL(vfs_ioc_fssetxattr_check);