| From e72b9dd6a5f17d0fb51f16f8685f3004361e83d0 Mon Sep 17 00:00:00 2001 |
| From: Al Viro <viro@zeniv.linux.org.uk> |
| Date: Sun, 3 Nov 2019 13:45:04 -0500 |
| Subject: ecryptfs_lookup_interpose(): lower_dentry->d_inode is not stable |
| |
| From: Al Viro <viro@zeniv.linux.org.uk> |
| |
| 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 <viro@zeniv.linux.org.uk> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| |
| --- |
| fs/ecryptfs/inode.c | 12 ++++++++++-- |
| 1 file changed, 10 insertions(+), 2 deletions(-) |
| |
| --- a/fs/ecryptfs/inode.c |
| +++ b/fs/ecryptfs/inode.c |
| @@ -325,7 +325,7 @@ static int ecryptfs_i_size_read(struct d |
| 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; |
| @@ -345,7 +345,15 @@ static struct dentry *ecryptfs_lookup_in |
| 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; |