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>
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1 changed files with 3 additions and 4 deletions
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@ -330,9 +330,9 @@ static int ecryptfs_lookup_interpose(struct dentry *dentry,
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struct dentry *lower_dentry,
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struct inode *dir_inode)
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{
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struct path *path = ecryptfs_dentry_to_lower_path(dentry->d_parent);
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struct inode *inode, *lower_inode;
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struct ecryptfs_dentry_info *dentry_info;
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struct vfsmount *lower_mnt;
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int rc = 0;
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dentry_info = kmem_cache_alloc(ecryptfs_dentry_info_cache, GFP_KERNEL);
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@ -344,12 +344,11 @@ static int ecryptfs_lookup_interpose(struct dentry *dentry,
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return -ENOMEM;
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}
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lower_mnt = mntget(ecryptfs_dentry_to_lower_mnt(dentry->d_parent));
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fsstack_copy_attr_atime(dir_inode, d_inode(lower_dentry->d_parent));
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fsstack_copy_attr_atime(dir_inode, d_inode(path->dentry));
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BUG_ON(!d_count(lower_dentry));
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ecryptfs_set_dentry_private(dentry, dentry_info);
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dentry_info->lower_path.mnt = lower_mnt;
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dentry_info->lower_path.mnt = mntget(path->mnt);
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dentry_info->lower_path.dentry = lower_dentry;
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/*
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