From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-io0-f196.google.com ([209.85.223.196]:51449 "EHLO mail-io0-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751651AbdJZU6L (ORCPT ); Thu, 26 Oct 2017 16:58:11 -0400 From: Eric Biggers To: keyrings@vger.kernel.org Cc: David Howells , Ben Hutchings , Xiao Yang , David Safford , Mimi Zohar , linux-security-module@vger.kernel.org, Eric Biggers , stable@vger.kernel.org Subject: [PATCH] KEYS: trusted: fix writing past end of buffer in trusted_read() Date: Thu, 26 Oct 2017 13:57:44 -0700 Message-Id: <20171026205744.105566-1-ebiggers3@gmail.com> Sender: stable-owner@vger.kernel.org List-ID: From: Eric Biggers When calling keyctl_read() on a key of type "trusted", if the user-supplied buffer was too small, the kernel ignored the buffer length and just wrote past the end of the buffer, potentially corrupting userspace memory. Fix it by instead returning the size required, as per the documentation for keyctl_read(). We also don't even fill the buffer at all in this case, as this is slightly easier to implement than doing a short read, and either behavior appears to be permitted. It also makes it match the behavior of the "encrypted" key type. Fixes: d00a1c72f7f4 ("keys: add new trusted key-type") Reported-by: Ben Hutchings Cc: # v2.6.38+ Signed-off-by: Eric Biggers --- security/keys/trusted.c | 23 ++++++++++++----------- 1 file changed, 12 insertions(+), 11 deletions(-) diff --git a/security/keys/trusted.c b/security/keys/trusted.c index bd85315cbfeb..98aa89ff7bfd 100644 --- a/security/keys/trusted.c +++ b/security/keys/trusted.c @@ -1147,20 +1147,21 @@ static long trusted_read(const struct key *key, char __user *buffer, p = dereference_key_locked(key); if (!p) return -EINVAL; - if (!buffer || buflen <= 0) - return 2 * p->blob_len; - ascii_buf = kmalloc(2 * p->blob_len, GFP_KERNEL); - if (!ascii_buf) - return -ENOMEM; - bufp = ascii_buf; - for (i = 0; i < p->blob_len; i++) - bufp = hex_byte_pack(bufp, p->blob[i]); - if ((copy_to_user(buffer, ascii_buf, 2 * p->blob_len)) != 0) { + if (buffer && buflen >= 2 * p->blob_len) { + ascii_buf = kmalloc(2 * p->blob_len, GFP_KERNEL); + if (!ascii_buf) + return -ENOMEM; + + bufp = ascii_buf; + for (i = 0; i < p->blob_len; i++) + bufp = hex_byte_pack(bufp, p->blob[i]); + if (copy_to_user(buffer, ascii_buf, 2 * p->blob_len) != 0) { + kzfree(ascii_buf); + return -EFAULT; + } kzfree(ascii_buf); - return -EFAULT; } - kzfree(ascii_buf); return 2 * p->blob_len; } -- 2.15.0.rc2.357.g7e34df9404-goog