| From | lizf@kernel ... | Subject | [PATCH 3.4 055/146] RCU pathwalk breakage when running into a symlink overmounting something | Date | Tue, 15 Sep 2015 17:02:50 +0800 |
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From: Al Viro <viro@zeniv.linux.org.uk>
3.4.109-rc1 review patch. If anyone has any objections, please let me know.
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commit 3cab989afd8d8d1bc3d99fef0e7ed87c31e7b647 upstream.
Calling unlazy_walk() in walk_component() and do_last() when we find a symlink that needs to be followed doesn't acquire a reference to vfsmount. That's fine when the symlink is on the same vfsmount as the parent directory (which is almost always the case), but it's not always true - one _can_ manage to bind a symlink on top of something. And in such cases we end up with excessive mntput().
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk> [lizf: Backported to 3.4: drop the changes to do_last()] Signed-off-by: Zefan Li <lizefan@huawei.com> --- fs/namei.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/fs/namei.c b/fs/namei.c index bdcd705..9c4b9b8 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -1314,7 +1314,8 @@ static inline int walk_component(struct nameidata *nd, struct path *path, } if (should_follow_link(inode, follow)) { if (nd->flags & LOOKUP_RCU) { - if (unlikely(unlazy_walk(nd, path->dentry))) { + if (unlikely(nd->path.mnt != path->mnt || + unlazy_walk(nd, path->dentry))) { terminate_walk(nd); return -ECHILD; } -- 1.9.1
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