[PATCH] namei fixes (9/19) (463ffb2e) · Commits · 戴 / test

New helper: __follow_mount(struct path *path). Same as follow_mount(), except that we do *not* do mntput() after the first lookup_mnt(). IOW, original path->mnt stays pinned down. We also take care to do dput() before mntput() in the loop body (follow_mount() also needs that reordering, but that will be done later in the series). The following are equivalent, assuming that path.mnt == x: (1) follow_mount(&path.mnt, &path.dentry) (2) __follow_mount(&path); if (path->mnt != x) mntput(x); (3) if (__follow_mount(&path)) mntput(x); Callers of follow_mount() in __link_path_walk() converted to (2). Equivalent transformation + fix for too-late-mntput() race in __follow_mount() loop. Signed-off-by:

Al Viro <viro@parcelfarce.linux.theplanet.co.uk> Signed-off-by:

Andrew Morton <akpm@osdl.org> Signed-off-by:

Linus Torvalds <torvalds@osdl.org>

fs/namei.c

+23 −2

Original line number	Diff line number	Diff line
		@@ -576,6 +576,23 @@ int follow_up(struct vfsmount mnt, struct dentry dentry)
		/* no need for dcache_lock, as serialization is taken care in
		* namespace.c
		*/
		static int __follow_mount(struct path *path)
		{
		int res = 0;
		while (d_mountpoint(path->dentry)) {
		struct vfsmount *mounted = lookup_mnt(path->mnt, path->dentry);
		if (!mounted)
		break;
		dput(path->dentry);
		if (res)
		mntput(path->mnt);
		path->mnt = mounted;
		path->dentry = dget(mounted->mnt_root);
		res = 1;
		}
		return res;
		}

		static int follow_mount(struct vfsmount mnt, struct dentry dentry)
		{
		int res = 0;
		@@ -778,7 +795,9 @@ static fastcall int __link_path_walk(const char * name, struct nameidata *nd)
		if (err)
		break;
		/* Check mountpoints.. */
		follow_mount(&next.mnt, &next.dentry);
		__follow_mount(&next);
		if (nd->mnt != next.mnt)
		mntput(nd->mnt);

		err = -ENOENT;
		inode = next.dentry->d_inode;
		@@ -836,7 +855,9 @@ last_component:
		err = do_lookup(nd, &this, &next);
		if (err)
		break;
		follow_mount(&next.mnt, &next.dentry);
		__follow_mount(&next);
		if (nd->mnt != next.mnt)
		mntput(nd->mnt);
		inode = next.dentry->d_inode;
		if ((lookup_flags & LOOKUP_FOLLOW)
		&& inode && inode->i_op && inode->i_op->follow_link) {

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