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| author | Al Viro <viro@zeniv.linux.org.uk> | 2019-11-03 21:55:43 +0300 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2019-11-20 19:59:32 +0300 |
| commit | d47135249f4d1e8d29e514986a63bf129c64276c (patch) | |
| tree | a75e5a1bf88ea14e6b1ad6b329953e10f3d88555 | |
| parent | dc39d4f7ecbd4176b4e358c8caf9b8f18c8f8e24 (diff) | |
| download | linux-d47135249f4d1e8d29e514986a63bf129c64276c.tar.xz | |
ecryptfs_lookup_interpose(): lower_dentry->d_parent is not stable either
commit 762c69685ff7ad5ad7fee0656671e20a0c9c864d upstream.
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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
| -rw-r--r-- | fs/ecryptfs/inode.c | 7 |
1 files changed, 3 insertions, 4 deletions
diff --git a/fs/ecryptfs/inode.c b/fs/ecryptfs/inode.c index d40229ccb6a9..62d1dea85ef1 100644 --- a/fs/ecryptfs/inode.c +++ b/fs/ecryptfs/inode.c @@ -326,9 +326,9 @@ 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); @@ -340,13 +340,12 @@ 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; /* |