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 @@ -326,9 +326,9 @@ 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); @@ -340,13 +340,12 @@ 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;
/*