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authorAmir Goldstein <amir73il@gmail.com>2018-05-11 11:15:15 +0300
committerMiklos Szeredi <mszeredi@redhat.com>2018-05-31 12:06:12 +0300
commit01b39dcc95680b04c7af5de7f39f577e9c4865e3 (patch)
tree18675377623d5ef108a90a72a9b523cf535e4210 /fs/overlayfs/dir.c
parentac6a52eb65b5327859135269c9374bf2ff731c9f (diff)
downloadlinux-01b39dcc95680b04c7af5de7f39f577e9c4865e3.tar.xz
ovl: use inode_insert5() to hash a newly created inode
Currently, there is a small window where ovl_obtain_alias() can race with ovl_instantiate() and create two different overlay inodes with the same underlying real non-dir non-hardlink inode. The race requires an adversary to guess the file handle of the yet to be created upper inode and decode the guessed file handle after ovl_creat_real(), but before ovl_instantiate(). This race does not affect overlay directory inodes, because those are decoded via ovl_lookup_real() and not with ovl_obtain_alias(). This patch fixes the race, by using inode_insert5() to add a newly created inode to cache. If the newly created inode apears to already exist in cache (hashed by the same real upper inode), we instantiate the dentry with the old inode and drop the new inode, instead of silently not hashing the new inode. Signed-off-by: Amir Goldstein <amir73il@gmail.com> Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Diffstat (limited to 'fs/overlayfs/dir.c')
-rw-r--r--fs/overlayfs/dir.c59
1 files changed, 49 insertions, 10 deletions
diff --git a/fs/overlayfs/dir.c b/fs/overlayfs/dir.c
index e8c7df070fed..f480b1a2cd2e 100644
--- a/fs/overlayfs/dir.c
+++ b/fs/overlayfs/dir.c
@@ -229,24 +229,54 @@ static int ovl_set_opaque(struct dentry *dentry, struct dentry *upperdentry)
return ovl_set_opaque_xerr(dentry, upperdentry, -EIO);
}
-/* Common operations required to be done after creation of file on upper */
-static void ovl_instantiate(struct dentry *dentry, struct inode *inode,
- struct dentry *newdentry, bool hardlink)
+/*
+ * Common operations required to be done after creation of file on upper.
+ * If @hardlink is false, then @inode is a pre-allocated inode, we may or
+ * may not use to instantiate the new dentry.
+ */
+static int ovl_instantiate(struct dentry *dentry, struct inode *inode,
+ struct dentry *newdentry, bool hardlink)
{
+ struct ovl_inode_params oip = {
+ .upperdentry = newdentry,
+ .newinode = inode,
+ };
+
ovl_dentry_version_inc(dentry->d_parent, false);
ovl_dentry_set_upper_alias(dentry);
if (!hardlink) {
- ovl_inode_update(inode, newdentry);
- ovl_copyattr(newdentry->d_inode, inode);
+ /*
+ * ovl_obtain_alias() can be called after ovl_create_real()
+ * and before we get here, so we may get an inode from cache
+ * with the same real upperdentry that is not the inode we
+ * pre-allocated. In this case we will use the cached inode
+ * to instantiate the new dentry.
+ *
+ * XXX: if we ever use ovl_obtain_alias() to decode directory
+ * file handles, need to use ovl_get_inode_locked() and
+ * d_instantiate_new() here to prevent from creating two
+ * hashed directory inode aliases.
+ */
+ inode = ovl_get_inode(dentry->d_sb, &oip);
+ if (WARN_ON(IS_ERR(inode)))
+ return PTR_ERR(inode);
} else {
WARN_ON(ovl_inode_real(inode) != d_inode(newdentry));
dput(newdentry);
inc_nlink(inode);
}
+
d_instantiate(dentry, inode);
+ if (inode != oip.newinode) {
+ pr_warn_ratelimited("overlayfs: newly created inode found in cache (%pd2)\n",
+ dentry);
+ }
+
/* Force lookup of new upper hardlink to find its lower */
if (hardlink)
d_drop(dentry);
+
+ return 0;
}
static bool ovl_type_merge(struct dentry *dentry)
@@ -285,11 +315,17 @@ static int ovl_create_upper(struct dentry *dentry, struct inode *inode,
ovl_set_opaque(dentry, newdentry);
}
- ovl_instantiate(dentry, inode, newdentry, !!attr->hardlink);
- err = 0;
+ err = ovl_instantiate(dentry, inode, newdentry, !!attr->hardlink);
+ if (err)
+ goto out_cleanup;
out_unlock:
inode_unlock(udir);
return err;
+
+out_cleanup:
+ ovl_cleanup(udir, newdentry);
+ dput(newdentry);
+ goto out_unlock;
}
static struct dentry *ovl_clear_empty(struct dentry *dentry,
@@ -474,8 +510,9 @@ static int ovl_create_over_whiteout(struct dentry *dentry, struct inode *inode,
if (err)
goto out_cleanup;
}
- ovl_instantiate(dentry, inode, newdentry, hardlink);
- err = 0;
+ err = ovl_instantiate(dentry, inode, newdentry, hardlink);
+ if (err)
+ goto out_cleanup;
out_dput:
dput(upper);
out_unlock:
@@ -558,6 +595,7 @@ static int ovl_create_object(struct dentry *dentry, int mode, dev_t rdev,
if (err)
goto out;
+ /* Preallocate inode to be used by ovl_get_inode() */
err = -ENOMEM;
inode = ovl_new_inode(dentry->d_sb, mode, rdev);
if (!inode)
@@ -567,7 +605,8 @@ static int ovl_create_object(struct dentry *dentry, int mode, dev_t rdev,
attr.mode = inode->i_mode;
err = ovl_create_or_link(dentry, inode, &attr, false);
- if (err)
+ /* Did we end up using the preallocated inode? */
+ if (inode != d_inode(dentry))
iput(inode);
out_drop_write: