ecryptfs_lookup_interpose(): lower_dentry->d_parent is not stable either (762c6968) · Commits · 戴 / test

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>

fs/ecryptfs/inode.c

+3 −4

Original line number	Diff line number	Diff line
		@@ -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;

		/*

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