vfs: make follow_link check RCU safe

This will allow this code to be used in RCU mode.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 10 insertions, 2 deletions

diff --git a/fs/namei.c b/fs/namei.c
index 41445e7fd339..c6b996817bb3 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2201,6 +2201,7 @@ static struct file *do_last(struct nameidata *nd, struct path *path,
         int acc_mode = op->acc_mode;
         struct file *filp;
         struct inode *inode;
+        int symlink_ok = 0;
         int error;
 
         nd->flags &= ~LOOKUP_PARENT;
@@ -2232,7 +2233,6 @@ static struct file *do_last(struct nameidata *nd, struct path *path,
         }
 
         if (!(open_flag & O_CREAT)) {
-                int symlink_ok = 0;
                 if (nd->last.name[nd->last.len])
                         nd->flags |= LOOKUP_FOLLOW | LOOKUP_DIRECTORY;
                 if (open_flag & O_PATH && !(nd->flags & LOOKUP_FOLLOW))
@@ -2364,8 +2364,16 @@ static struct file *do_last(struct nameidata *nd, struct path *path,
         if (!inode)
                 goto exit_dput;
 
-        if (inode->i_op->follow_link)
+        if (should_follow_link(inode, !symlink_ok)) {
+                if (nd->flags & LOOKUP_RCU) {
+                        if (unlikely(unlazy_walk(nd, path->dentry))) {
+                                error = -ECHILD;
+                                goto exit;
+                        }
+                }
+                BUG_ON(inode != path->dentry->d_inode);
                 return NULL;
+        }
 
         path_to_nameidata(path, nd);
         nd->inode = inode;