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Subject[PATCH 07/11] ovl: make ovl_create_real() cope with vfs_mkdir() safely
Date
From: Amir Goldstein <amir73il@gmail.com>

vfs_mkdir() may succeed and leave the dentry passed to it unhashed and
negative. ovl_create_real() is the last caller breaking when that
happens.

[amir: split re-factoring of ovl_create_temp() to prep patch
add comment about unhashed dir after mkdir
add pr_warn() if mkdir succeeds and lookup fails]

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
---
fs/overlayfs/dir.c | 35 +++++++++++++++++++++++++++++++++--
1 file changed, 33 insertions(+), 2 deletions(-)

diff --git a/fs/overlayfs/dir.c b/fs/overlayfs/dir.c
index 1b181292a624..b33d37d1a87c 100644
--- a/fs/overlayfs/dir.c
+++ b/fs/overlayfs/dir.c
@@ -114,6 +114,37 @@ int ovl_cleanup_and_whiteout(struct dentry *workdir, struct inode *dir,
goto out;
}

+static struct dentry *ovl_mkdir_real(struct inode *dir, struct dentry *dentry,
+ umode_t mode)
+{
+ int err;
+
+ err = ovl_do_mkdir(dir, dentry, mode);
+ if (err) {
+ dput(dentry);
+ return ERR_PTR(err);
+ }
+
+ /*
+ * vfs_mkdir() may succeed and leave the dentry passed
+ * to it unhashed and negative. If that happens, try to
+ * lookup a new hashed and positive dentry.
+ */
+ if (unlikely(d_unhashed(dentry))) {
+ struct dentry *d;
+
+ d = lookup_one_len(dentry->d_name.name, dentry->d_parent,
+ dentry->d_name.len);
+ if (IS_ERR(d)) {
+ pr_warn("overlayfs: failed lookup after mkdir (%pd2, err=%i).\n",
+ dentry, err);
+ }
+ dput(dentry);
+ dentry = d;
+ }
+ return dentry;
+}
+
struct dentry *ovl_create_real(struct inode *dir, struct dentry *newdentry,
struct ovl_cattr *attr)
{
@@ -135,8 +166,8 @@ struct dentry *ovl_create_real(struct inode *dir, struct dentry *newdentry,
break;

case S_IFDIR:
- err = ovl_do_mkdir(dir, newdentry, attr->mode);
- break;
+ /* mkdir is special... */
+ return ovl_mkdir_real(dir, newdentry, attr->mode);

case S_IFCHR:
case S_IFBLK:
--
2.14.3
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