From e72b9dd6a5f17d0fb51f16f8685f3004361e83d0 Mon Sep 17 00:00:00 2001 From: Al Viro Date: Sun, 3 Nov 2019 13:45:04 -0500 Subject: [Backport e72b9dd6a5f1] ecryptfs_lookup_interpose(): lower_dentry->d_inode is not stable 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 --- src/inode.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-) diff --git a/src/inode.c b/src/inode.c index a905d5f4f3b0726303595e39ba40309d68baa422..3c229872135987fb4d0a1a36a910651d5f37a08b 100644 --- a/src/inode.c +++ b/src/inode.c @@ -319,7 +319,7 @@ static int ecryptfs_i_size_read(struct dentry *dentry, struct inode *inode) static struct dentry *ecryptfs_lookup_interpose(struct dentry *dentry, struct dentry *lower_dentry) { - 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; @@ -339,7 +339,15 @@ static struct dentry *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 NULL; -- 2.31.1