From mboxrd@z Thu Jan 1 00:00:00 1970 From: Al Viro Subject: [PATCH][RFC] ecryptfs_lookup_interpose(): lower_dentry->d_parent is not stable either Date: Sun, 3 Nov 2019 19:03:23 +0000 Message-ID: <20191103190323.GS26530@ZenIV.linux.org.uk> References: <20191022133855.B1B4752050@d06av21.portsmouth.uk.ibm.com> <20191022143736.GX26530@ZenIV.linux.org.uk> <20191022201131.GZ26530@ZenIV.linux.org.uk> <20191023110551.D04AE4C044@d06av22.portsmouth.uk.ibm.com> <20191101234622.GM26530@ZenIV.linux.org.uk> <20191102172229.GT20975@paulmck-ThinkPad-P72> <20191102180842.GN26530@ZenIV.linux.org.uk> <20191103163524.GO26530@ZenIV.linux.org.uk> <20191103182058.GQ26530@ZenIV.linux.org.uk> <20191103185133.GR26530@ZenIV.linux.org.uk> Mime-Version: 1.0 Return-path: Content-Disposition: inline In-Reply-To: <20191103185133.GR26530@ZenIV.linux.org.uk> Sender: linux-kernel-owner@vger.kernel.org List-ID: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: linux-fsdevel@vger.kernel.org Cc: Ritesh Harjani , linux-kernel@vger.kernel.org, wugyuan@cn.ibm.com, jlayton@kernel.org, hsiangkao@aol.com, Jan Kara , Linus Torvalds , ecryptfs@vger.kernel.org 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 diff --git a/fs/ecryptfs/inode.c b/fs/ecryptfs/inode.c index 3c2298721359..e23752d9a79f 100644 --- a/fs/ecryptfs/inode.c +++ b/fs/ecryptfs/inode.c @@ -319,9 +319,9 @@ 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 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); @@ -330,13 +330,12 @@ static struct dentry *ecryptfs_lookup_interpose(struct dentry *dentry, 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; /*