From 39159de2a091a35ea86b188ebdc5e642f5cfc832 Mon Sep 17 00:00:00 2001 From: Jeff Layton Date: Mon, 7 Dec 2009 12:01:50 -0500 Subject: [PATCH] vfs: force reval of target when following LAST_BIND symlinks (try #7) procfs-style symlinks return a last_type of LAST_BIND without an actual path string. This causes __follow_link to skip calling __vfs_follow_link and so the dentry isn't revalidated. This is a problem when the link target sits on NFSv4 as it depends on the VFS to revalidate the dentry before using it on an open call. Ensure that this occurs by forcing a revalidation of the target dentry of LAST_BIND symlinks. Signed-off-by: Jeff Layton Acked-by: "Eric W. Biederman" Acked-by: Miklos Szeredi Signed-off-by: Al Viro --- fs/namei.c | 45 +++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 45 insertions(+) diff --git a/fs/namei.c b/fs/namei.c index a765e7a741f4..d2783c8a770b 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -413,6 +413,46 @@ do_revalidate(struct dentry *dentry, struct nameidata *nd) return dentry; } +/* + * force_reval_path - force revalidation of a dentry + * + * In some situations the path walking code will trust dentries without + * revalidating them. This causes problems for filesystems that depend on + * d_revalidate to handle file opens (e.g. NFSv4). When FS_REVAL_DOT is set + * (which indicates that it's possible for the dentry to go stale), force + * a d_revalidate call before proceeding. + * + * Returns 0 if the revalidation was successful. If the revalidation fails, + * either return the error returned by d_revalidate or -ESTALE if the + * revalidation it just returned 0. If d_revalidate returns 0, we attempt to + * invalidate the dentry. It's up to the caller to handle putting references + * to the path if necessary. + */ +static int +force_reval_path(struct path *path, struct nameidata *nd) +{ + int status; + struct dentry *dentry = path->dentry; + + /* + * only check on filesystems where it's possible for the dentry to + * become stale. It's assumed that if this flag is set then the + * d_revalidate op will also be defined. + */ + if (!(dentry->d_sb->s_type->fs_flags & FS_REVAL_DOT)) + return 0; + + status = dentry->d_op->d_revalidate(dentry, nd); + if (status > 0) + return 0; + + if (!status) { + d_invalidate(dentry); + status = -ESTALE; + } + return status; +} + /* * Short-cut version of permission(), for calling on directories * during pathname resolution. Combines parts of permission() @@ -529,6 +569,11 @@ static __always_inline int __do_follow_link(struct path *path, struct nameidata error = 0; if (s) error = __vfs_follow_link(nd, s); + else if (nd->last_type == LAST_BIND) { + error = force_reval_path(&nd->path, nd); + if (error) + path_put(&nd->path); + } if (dentry->d_inode->i_op->put_link) dentry->d_inode->i_op->put_link(dentry, nd, cookie); } -- 2.20.1