1 files changed, 43 insertions, 4 deletions

diff --git a/fs/namei.c b/fs/namei.c
index 1d4d17f24fb2..25cc9680e6dc 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -540,10 +540,13 @@ static inline int do_inode_permission(struct mnt_idmap *idmap,
  * @mask: Right to check for (%MAY_READ, %MAY_WRITE, %MAY_EXEC)
  *
  * Separate out file-system wide checks from inode-specific permission checks.
+ *
+ * Note: lookup_inode_permission_may_exec() does not call here. If you add
+ * MAY_EXEC checks, adjust it.
  */
 static int sb_permission(struct super_block *sb, struct inode *inode, int mask)
 {
-	if (unlikely(mask & MAY_WRITE)) {
+	if (mask & MAY_WRITE) {
 		umode_t mode = inode->i_mode;
 
 		/* Nobody gets write access to a read-only fs. */
@@ -574,7 +577,7 @@ int inode_permission(struct mnt_idmap *idmap,
 	if (unlikely(retval))
 		return retval;
 
-	if (unlikely(mask & MAY_WRITE)) {
+	if (mask & MAY_WRITE) {
 		/*
 		 * Nobody gets write access to an immutable file.
 		 */
@@ -602,6 +605,42 @@ int inode_permission(struct mnt_idmap *idmap,
 }
 EXPORT_SYMBOL(inode_permission);
 
+/*
+ * lookup_inode_permission_may_exec - Check traversal right for given inode
+ *
+ * This is a special case routine for may_lookup() making assumptions specific
+ * to path traversal. Use inode_permission() if you are doing something else.
+ *
+ * Work is shaved off compared to inode_permission() as follows:
+ * - we know for a fact there is no MAY_WRITE to worry about
+ * - it is an invariant the inode is a directory
+ *
+ * Since majority of real-world traversal happens on inodes which grant it for
+ * everyone, we check it upfront and only resort to more expensive work if it
+ * fails.
+ *
+ * Filesystems which have their own ->permission hook and consequently miss out
+ * on IOP_FASTPERM can still get the optimization if they set IOP_FASTPERM_MAY_EXEC
+ * on their directory inodes.
+ */
+static __always_inline int lookup_inode_permission_may_exec(struct mnt_idmap *idmap,
+	struct inode *inode, int mask)
+{
+	/* Lookup already checked this to return -ENOTDIR */
+	VFS_BUG_ON_INODE(!S_ISDIR(inode->i_mode), inode);
+	VFS_BUG_ON((mask & ~MAY_NOT_BLOCK) != 0);
+
+	mask |= MAY_EXEC;
+
+	if (unlikely(!(inode->i_opflags & (IOP_FASTPERM | IOP_FASTPERM_MAY_EXEC))))
+		return inode_permission(idmap, inode, mask);
+
+	if (unlikely(((inode->i_mode & 0111) != 0111) || !no_acl_inode(inode)))
+		return inode_permission(idmap, inode, mask);
+
+	return security_inode_permission(inode, mask);
+}
+
 /**
  * path_get - get a reference to a path
  * @path: path to get the reference to
@@ -1855,7 +1894,7 @@ static inline int may_lookup(struct mnt_idmap *idmap,
 	int err, mask;
 
 	mask = nd->flags & LOOKUP_RCU ? MAY_NOT_BLOCK : 0;
-	err = inode_permission(idmap, nd->inode, mask | MAY_EXEC);
+	err = lookup_inode_permission_may_exec(idmap, nd->inode, mask);
 	if (likely(!err))
 		return 0;
 
@@ -1870,7 +1909,7 @@ static inline int may_lookup(struct mnt_idmap *idmap,
 	if (err != -ECHILD)	// hard error
 		return err;
 
-	return inode_permission(idmap, nd->inode, MAY_EXEC);
+	return lookup_inode_permission_may_exec(idmap, nd->inode, 0);
 }
 
 static int reserve_stack(struct nameidata *nd, struct path *link)