From: Al Viro Date: Sun, 3 Nov 2019 18:45:04 +0000 (-0500) Subject: ecryptfs_lookup_interpose(): lower_dentry->d_inode is not stable X-Git-Url: http://git.osdn.net/view?a=commitdiff_plain;h=c3c7cfbe975cf1b0b5f3c5fa7745851a4afa1053;p=sagit-ice-cold%2Fkernel_xiaomi_msm8998.git ecryptfs_lookup_interpose(): lower_dentry->d_inode is not stable commit e72b9dd6a5f17d0fb51f16f8685f3004361e83d0 upstream. lower_dentry can't go from positive to negative (we have it pinned), but it *can* go from negative to positive. So fetching ->d_inode into a local variable, doing a blocking allocation, checking that now ->d_inode is non-NULL and feeding the value we'd fetched earlier to a function that won't accept NULL is not a good idea. Cc: stable@vger.kernel.org Signed-off-by: Al Viro Signed-off-by: Greg Kroah-Hartman --- diff --git a/fs/ecryptfs/inode.c b/fs/ecryptfs/inode.c index 844d0c4da84f..ff69c260a3b3 100644 --- a/fs/ecryptfs/inode.c +++ b/fs/ecryptfs/inode.c @@ -330,7 +330,7 @@ static int ecryptfs_lookup_interpose(struct dentry *dentry, struct dentry *lower_dentry, struct inode *dir_inode) { - struct inode *inode, *lower_inode = d_inode(lower_dentry); + struct inode *inode, *lower_inode; struct ecryptfs_dentry_info *dentry_info; struct vfsmount *lower_mnt; int rc = 0; @@ -352,7 +352,15 @@ static int ecryptfs_lookup_interpose(struct dentry *dentry, dentry_info->lower_path.mnt = lower_mnt; dentry_info->lower_path.dentry = lower_dentry; - if (d_really_is_negative(lower_dentry)) { + /* + * negative dentry can go positive under us here - its parent is not + * locked. That's OK and that could happen just as we return from + * ecryptfs_lookup() anyway. Just need to be careful and fetch + * ->d_inode only once - it's not stable here. + */ + lower_inode = READ_ONCE(lower_dentry->d_inode); + + if (!lower_inode) { /* We want to add because we couldn't find in lower */ d_add(dentry, NULL); return 0;