Commit d0e13f5b authored Jun 15, 2016 by Miklos Szeredi

ovl: fix uid/gid when creating over whiteout



Fix a regression when creating a file over a whiteout.  The new
file/directory needs to use the current fsuid/fsgid, not the ones from the
mounter's credentials.

The refcounting is a bit tricky: prepare_creds() sets an original refcount,
override_creds() gets one more, which revert_cred() drops.  So

  1) we need to expicitly put the mounter's credentials when overriding
     with the updated one

  2) we need to put the original ref to the updated creds (and this can
     safely be done before revert_creds(), since we'll still have the ref
     from override_creds()).

Reported-by: Stephen Smalley <sds@tycho.nsa.gov>
Fixes: 3fe6e52f ("ovl: override creds with the ones from the superblock mounter")
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

parent 30402c89

fs/overlayfs/dir.c

+11 −2

Original line number	Diff line number	Diff line
		@@ -405,12 +405,21 @@ static int ovl_create_or_link(struct dentry *dentry, int mode, dev_t rdev,
		err = ovl_create_upper(dentry, inode, &stat, link, hardlink);
		} else {
		const struct cred *old_cred;
		struct cred *override_cred;

		old_cred = ovl_override_creds(dentry->d_sb);

		err = ovl_create_over_whiteout(dentry, inode, &stat, link,
		hardlink);
		err = -ENOMEM;
		override_cred = prepare_creds();
		if (override_cred) {
		override_cred->fsuid = old_cred->fsuid;
		override_cred->fsgid = old_cred->fsgid;
		put_cred(override_creds(override_cred));
		put_cred(override_cred);

		err = ovl_create_over_whiteout(dentry, inode, &stat,
		link, hardlink);
		}
		revert_creds(old_cred);
		}

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