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Commit 463ffb2e authored by Al Viro's avatar Al Viro Committed by Linus Torvalds
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[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: default avatarAl Viro <viro@parcelfarce.linux.theplanet.co.uk>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent d671d5e5

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 @@ static fastcall int __link_path_walk(const char * name, struct nameidata *nd) 
		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) {