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ecryptfs_lookup_interpose(): lower_dentry->d_inode is not stable

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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>
This commit is contained in:
Al Viro 2019-11-03 13:45:04 -05:00
parent bcf0d9d4b7
commit e72b9dd6a5
1 changed files with 10 additions and 2 deletions
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12
fs/ecryptfs/inode.c
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@ -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, static struct dentry *ecryptfs_lookup_interpose(struct dentry *dentry,
struct dentry *lower_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 ecryptfs_dentry_info *dentry_info;
struct vfsmount *lower_mnt; struct vfsmount *lower_mnt;
int rc = 0; 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.mnt = lower_mnt;
dentry_info->lower_path.dentry = lower_dentry; 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 */ /* We want to add because we couldn't find in lower */
d_add(dentry, NULL); d_add(dentry, NULL);
return NULL; return NULL;