| From 762c69685ff7ad5ad7fee0656671e20a0c9c864d Mon Sep 17 00:00:00 2001 |
| From: Al Viro <viro@zeniv.linux.org.uk> |
| Date: Sun, 3 Nov 2019 13:55:43 -0500 |
| Subject: ecryptfs_lookup_interpose(): lower_dentry->d_parent is not stable either |
| |
| From: Al Viro <viro@zeniv.linux.org.uk> |
| |
| commit 762c69685ff7ad5ad7fee0656671e20a0c9c864d upstream. |
| |
| We need to get the underlying dentry of parent; sure, absent the races |
| it is the parent of underlying dentry, but there's nothing to prevent |
| losing a timeslice to preemtion in the middle of evaluation of |
| lower_dentry->d_parent->d_inode, having another process move lower_dentry |
| around and have its (ex)parent not pinned anymore and freed on memory |
| pressure. Then we regain CPU and try to fetch ->d_inode from memory |
| that is freed by that point. |
| |
| dentry->d_parent *is* stable here - it's an argument of ->lookup() and |
| we are guaranteed that it won't be moved anywhere until we feed it |
| to d_add/d_splice_alias. So we safely go that way to get to its |
| underlying dentry. |
| |
| Cc: stable@vger.kernel.org # since 2009 or so |
| Signed-off-by: Al Viro <viro@zeniv.linux.org.uk> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| |
| --- |
| fs/ecryptfs/inode.c | 7 +++---- |
| 1 file changed, 3 insertions(+), 4 deletions(-) |
| |
| --- a/fs/ecryptfs/inode.c |
| +++ b/fs/ecryptfs/inode.c |
| @@ -325,9 +325,9 @@ static int ecryptfs_i_size_read(struct d |
| static struct dentry *ecryptfs_lookup_interpose(struct dentry *dentry, |
| struct dentry *lower_dentry) |
| { |
| + struct path *path = ecryptfs_dentry_to_lower_path(dentry->d_parent); |
| struct inode *inode, *lower_inode; |
| struct ecryptfs_dentry_info *dentry_info; |
| - struct vfsmount *lower_mnt; |
| int rc = 0; |
| |
| dentry_info = kmem_cache_alloc(ecryptfs_dentry_info_cache, GFP_KERNEL); |
| @@ -336,13 +336,12 @@ static struct dentry *ecryptfs_lookup_in |
| return ERR_PTR(-ENOMEM); |
| } |
| |
| - lower_mnt = mntget(ecryptfs_dentry_to_lower_mnt(dentry->d_parent)); |
| fsstack_copy_attr_atime(d_inode(dentry->d_parent), |
| - d_inode(lower_dentry->d_parent)); |
| + d_inode(path->dentry)); |
| BUG_ON(!d_count(lower_dentry)); |
| |
| ecryptfs_set_dentry_private(dentry, dentry_info); |
| - dentry_info->lower_path.mnt = lower_mnt; |
| + dentry_info->lower_path.mnt = mntget(path->mnt); |
| dentry_info->lower_path.dentry = lower_dentry; |
| |
| /* |