switch non-create side of open() to use of do_last()

Instead of path_lookupat() doing trailing symlink resolution,
use the same scheme as on the O_CREAT side.  Walk with
LOOKUP_PARENT, then (in do_last()) look the final component
up, then either open it or return error or, if it's a symlink,
give the symlink back to path_openat() to be resolved there.

The really messy complication here is RCU.  We don't want to drop
out of RCU mode before the final lookup, since we don't want to
bounce parent directory ->d_count without a good reason.

Result is _not_ pretty; later in the series we'll clean it up.
For now we are roughly back where we'd been before the revert
done by Nick's series - top-level logics of path_openat() is
cleaned up, do_last() does actual opening, symlink resolution is
done uniformly.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --git a/fs/namei.c b/fs/namei.c
index a260a306daf51e077fa67e54f7523df74f937b56..9595b4a55c3961eafe1396c17581cacb3b768e1b 100644 (file)
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2178,13 +2178,14 @@ exit:
 }
 
 /*
- * Handle O_CREAT case for do_filp_open
+ * Handle the last step of open()
  */
 static struct file *do_last(struct nameidata *nd, struct path *path,
                            const struct open_flags *op, const char *pathname)
 {
        struct dentry *dir = nd->path.dentry;
        struct file *filp;
+       struct inode *inode;
        int error;
 
        nd->flags &= ~LOOKUP_PARENT;
@@ -2192,17 +2193,27 @@ static struct file *do_last(struct nameidata *nd, struct path *path,
 
        switch (nd->last_type) {
        case LAST_DOTDOT:
-               follow_dotdot(nd);
-               dir = nd->path.dentry;
        case LAST_DOT:
+               error = handle_dots(nd, nd->last_type);
+               if (error)
+                       return ERR_PTR(error);
                /* fallthrough */
        case LAST_ROOT:
+               if (nd->flags & LOOKUP_RCU) {
+                       if (nameidata_drop_rcu_last(nd))
+                               return ERR_PTR(-ECHILD);
+               }
                error = handle_reval_path(nd);
                if (error)
                        goto exit;
-               error = -EISDIR;
-               goto exit;
+               audit_inode(pathname, nd->path.dentry);
+               if (op->open_flag & O_CREAT) {
+                       error = -EISDIR;
+                       goto exit;
+               }
+               goto ok;
        case LAST_BIND:
+               /* can't be RCU mode here */
                error = handle_reval_path(nd);
                if (error)
                        goto exit;
@@ -2210,6 +2221,51 @@ static struct file *do_last(struct nameidata *nd, struct path *path,
                goto ok;
        }
 
+       if (!(op->open_flag & O_CREAT)) {
+               if (nd->last.name[nd->last.len])
+                       nd->flags |= LOOKUP_FOLLOW | LOOKUP_DIRECTORY;
+               /* we _can_ be in RCU mode here */
+               error = do_lookup(nd, &nd->last, path, &inode);
+               if (error) {
+                       terminate_walk(nd);
+                       return ERR_PTR(error);
+               }
+               if (!inode) {
+                       path_to_nameidata(path, nd);
+                       terminate_walk(nd);
+                       return ERR_PTR(-ENOENT);
+               }
+               if (unlikely(inode->i_op->follow_link)) {
+                       /* We drop rcu-walk here */
+                       if (nameidata_dentry_drop_rcu_maybe(nd, path->dentry))
+                               return ERR_PTR(-ECHILD);
+                       return NULL;
+               }
+               path_to_nameidata(path, nd);
+               nd->inode = inode;
+               /* sayonara */
+               if (nd->flags & LOOKUP_RCU) {
+                       if (nameidata_drop_rcu_last(nd))
+                               return ERR_PTR(-ECHILD);
+               }
+
+               error = -ENOTDIR;
+               if (nd->flags & LOOKUP_DIRECTORY) {
+                       if (!inode->i_op->lookup)
+                               goto exit;
+               }
+               audit_inode(pathname, nd->path.dentry);
+               goto ok;
+       }
+
+       /* create side of things */
+
+       if (nd->flags & LOOKUP_RCU) {
+               if (nameidata_drop_rcu_last(nd))
+                       return ERR_PTR(-ECHILD);
+       }
+
+       audit_inode(pathname, dir);
        error = -EISDIR;
        /* trailing slashes? */
        if (nd->last.name[nd->last.len])
@@ -2303,6 +2359,7 @@ exit:
 static struct file *path_openat(int dfd, const char *pathname,
                const struct open_flags *op, int flags)
 {
+       struct file *base = NULL;
        struct file *filp;
        struct nameidata nd;
        struct path path;
@@ -2318,39 +2375,15 @@ static struct file *path_openat(int dfd, const char *pathname,
        nd.intent.open.flags = open_to_namei_flags(op->open_flag);
        nd.intent.open.create_mode = op->mode;
 
-       if (op->open_flag & O_CREAT)
-               goto creat;
-
-       /* !O_CREAT, simple open */
-       error = path_lookupat(dfd, pathname, flags | op->intent, &nd);
+       error = path_init(dfd, pathname, flags | LOOKUP_PARENT, &nd, &base);
        if (unlikely(error))
                goto out_filp;
-       error = -ELOOP;
-       if (!(nd.flags & LOOKUP_FOLLOW)) {
-               if (nd.inode->i_op->follow_link)
-                       goto out_path;
-       }
-       error = -ENOTDIR;
-       if (nd.flags & LOOKUP_DIRECTORY) {
-               if (!nd.inode->i_op->lookup)
-                       goto out_path;
-       }
-       audit_inode(pathname, nd.path.dentry);
-       filp = finish_open(&nd, op->open_flag, op->acc_mode);
-       release_open_intent(&nd);
-       return filp;
 
-creat:
-       /* OK, have to create the file. Find the parent. */
-       error = path_lookupat(dfd, pathname, LOOKUP_PARENT | flags, &nd);
+       current->total_link_count = 0;
+       error = link_path_walk(pathname, &nd);
        if (unlikely(error))
                goto out_filp;
-       if (unlikely(!audit_dummy_context()))
-               audit_inode(pathname, nd.path.dentry);
 
-       /*
-        * We have the parent and last component.
-        */
        filp = do_last(&nd, &path, op, pathname);
        while (unlikely(!filp)) { /* trailing symlink */
                struct path link = path;
@@ -2386,12 +2419,13 @@ creat:
 out:
        if (nd.root.mnt)
                path_put(&nd.root);
+       if (base)
+               fput(base);
        release_open_intent(&nd);
        return filp;
 
 exit_dput:
        path_put_conditional(&path, &nd);
-out_path:
        path_put(&nd.path);
 out_filp:
        filp = ERR_PTR(error);