From 463ffb2e9d39c2a3fd8c3c1d4a34e01f2078f972 Mon Sep 17 00:00:00 2001 From: Al Viro Date: Mon, 6 Jun 2005 13:36:05 -0700 Subject: [PATCH] [PATCH] namei fixes (9/19) 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 Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/namei.c | 25 +++++++++++++++++++++++-- 1 file changed, 23 insertions(+), 2 deletions(-) diff --git a/fs/namei.c b/fs/namei.c index 3d08478d313..23a1ad46797 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -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) { -- 2.20.1