linux-kernel - [PATCH 3.16 182/212] KEYS: special dot prefixed keyring name bug fix

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Message-ID: <lsq.1496331796.233443293@decadent.org.uk>
Date:   Thu, 01 Jun 2017 16:43:16 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Mimi Zohar" <zohar@...ux.vnet.ibm.com>,
        "Dmitry Kasatkin" <d.kasatkin@...sung.com>,
        "David Howells" <dhowells@...hat.com>
Subject: [PATCH 3.16 182/212] KEYS: special dot prefixed keyring name bug fix

3.16.44-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Mimi Zohar <zohar@...ux.vnet.ibm.com>

commit a4e3b8d79a5c6d40f4a9703abf7fe3abcc6c3b8d upstream.

Dot prefixed keyring names are supposed to be reserved for the
kernel, but add_key() calls key_get_type_from_user(), which
incorrectly verifies the 'type' field, not the 'description' field.
This patch verifies the 'description' field isn't dot prefixed,
when creating a new keyring, and removes the dot prefix test in
key_get_type_from_user().

Changelog v6:
- whitespace and other cleanup

Changelog v5:
- Only prevent userspace from creating a dot prefixed keyring, not
  regular keys  - Dmitry

Reported-by: Dmitry Kasatkin <d.kasatkin@...sung.com>
Signed-off-by: Mimi Zohar <zohar@...ux.vnet.ibm.com>
Acked-by: David Howells <dhowells@...hat.com>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 security/keys/keyctl.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- a/security/keys/keyctl.c
+++ b/security/keys/keyctl.c
@@ -37,8 +37,6 @@ static int key_get_type_from_user(char *
 		return ret;
 	if (ret == 0 || ret >= len)
 		return -EINVAL;
-	if (type[0] == '.')
-		return -EPERM;
 	type[len - 1] = '\0';
 	return 0;
 }
@@ -86,6 +84,10 @@ SYSCALL_DEFINE5(add_key, const char __us
 		if (!*description) {
 			kfree(description);
 			description = NULL;
+		} else if ((description[0] == '.') &&
+			   (strncmp(type, "keyring", 7) == 0)) {
+			ret = -EPERM;
+			goto error2;
 		}
 	}