userns: unshare_userns(&cred) should not populate cred on failure

unshare_userns(new_cred) does *new_cred = prepare_creds() before create_user_ns() which can fail. However, the caller expects that it doesn't need to take care of new_cred if unshare_userns() fails. We could change the single caller, sys_unshare(), but I think it would be more clean to avoid the side effects on failure, so with this patch unshare_userns() does put_cred() itself and initializes *new_cred only if create_user_ns() succeeeds. Cc: stable@vger.kernel.org Signed-off-by: Oleg Nesterov <oleg@redhat.com> Reviewed-by: Andy Lutomirski <luto@amacapital.net> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

userns: unshare_userns(&cred) should not populate cred on failure
unshare_userns(new_cred) does *new_cred = prepare_creds() before create_user_ns() which can fail. However, the caller expects that it doesn't need to take care of new_cred if unshare_userns() fails. We could change the single caller, sys_unshare(), but I think it would be more clean to avoid the side effects on failure, so with this patch unshare_userns() does put_cred() itself and initializes *new_cred only if create_user_ns() succeeeds. Cc: stable@vger.kernel.org Signed-off-by: Oleg Nesterov <oleg@redhat.com> Reviewed-by: Andy Lutomirski <luto@amacapital.net> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Oleg Nesterov · Linus Torvalds
1 parent c095ba7224
Showing 1 changed file with 9 additions and 4 deletions Side-by-side Diff
kernel/user_namespace.c
@@ -105,16 +105,21 @@
 int unshare_userns(unsigned long unshare_flags, struct cred **new_cred)
 {
 	struct cred *cred;
+	int err = -ENOMEM;
  
 	if (!(unshare_flags & CLONE_NEWUSER))
 		return 0;
  
 	cred = prepare_creds();
-	if (!cred)
-		return -ENOMEM;
+	if (cred) {
+		err = create_user_ns(cred);
+		if (err)
+			put_cred(cred);
+		else
+			*new_cred = cred;
+	}
  
-	*new_cred = cred;
-	return create_user_ns(cred);
+	return err;
 }
  
 void free_user_ns(struct user_namespace *ns)
...	...	@@ -105,16 +105,21 @@
105	105	int unshare_userns(unsigned long unshare_flags, struct cred **new_cred)
106	106	{
107	107	struct cred *cred;
	108	+ int err = -ENOMEM;
108	109
109	110	if (!(unshare_flags & CLONE_NEWUSER))
110	111	return 0;
111	112
112	113	cred = prepare_creds();
113		- if (!cred)
114		- return -ENOMEM;
	114	+ if (cred) {
	115	+ err = create_user_ns(cred);
	116	+ if (err)
	117	+ put_cred(cred);
	118	+ else
	119	+ *new_cred = cred;
	120	+ }
115	121
116		- *new_cred = cred;
117		- return create_user_ns(cred);
	122	+ return err;
118	123	}
119	124
120	125	void free_user_ns(struct user_namespace *ns)