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Commit e72b9dd6 authored by Al Viro's avatar Al Viro
Browse files

ecryptfs_lookup_interpose(): lower_dentry->d_inode is not stable 



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: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent bcf0d9d4

fs/ecryptfs/inode.c

+10 −2
Original line number Diff line number Diff line
@@ -319,7 +319,7 @@ 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 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;
@@ -339,7 +339,15 @@ static struct dentry *ecryptfs_lookup_interpose(struct dentry *dentry, 
	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;