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authorAl Viro <viro@zeniv.linux.org.uk>2019-11-03 13:45:04 -0500
committerAl Viro <viro@zeniv.linux.org.uk>2019-11-10 11:57:44 -0500
commite72b9dd6a5f17d0fb51f16f8685f3004361e83d0 (patch)
tree19a562a037fad18df276c5847f43b57b646da2dc
parentbcf0d9d4b76976f892154efdfc509b256fd898e8 (diff)
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: Al Viro <viro@zeniv.linux.org.uk>
-rw-r--r--fs/ecryptfs/inode.c12
1 files changed, 10 insertions, 2 deletions
diff --git a/fs/ecryptfs/inode.c b/fs/ecryptfs/inode.c
index a905d5f4f3b0..3c2298721359 100644
--- a/fs/ecryptfs/inode.c
+++ b/fs/ecryptfs/inode.c
@@ -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;