From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-it0-f68.google.com ([209.85.214.68]:51253 "EHLO mail-it0-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751605AbeB1Buf (ORCPT ); Tue, 27 Feb 2018 20:50:35 -0500 From: Eric Biggers To: keyrings@vger.kernel.org, David Howells Cc: netdev@vger.kernel.org, Mark Rutland , Eric Biggers Subject: [PATCH] KEYS: DNS: limit the length of option strings Date: Tue, 27 Feb 2018 17:49:05 -0800 Message-Id: <20180228014905.68153-1-ebiggers3@gmail.com> Sender: netdev-owner@vger.kernel.org List-ID: From: Eric Biggers Adding a dns_resolver key whose payload contains a very long option name resulted in that string being printed in full. This hit the WARN_ONCE() in set_precision() during the printk(), because printk() only supports a precision of up to 32767 bytes: precision 1000000 too large WARNING: CPU: 0 PID: 752 at lib/vsprintf.c:2189 vsnprintf+0x4bc/0x5b0 Fix it by limiting option strings (combined name + value) to a much more reasonable 128 bytes. The exact limit is arbitrary, but currently the only recognized option is formatted as "dnserror=%lu" which fits well within this limit. Reproducer: perl -e 'print "#", "A" x 1000000, "\x00"' | keyctl padd dns_resolver desc @s This bug was found using syzkaller. Reported-by: Mark Rutland Fixes: 4a2d789267e0 ("DNS: If the DNS server returns an error, allow that to be cached [ver #2]") Cc: # v2.6.36+ Signed-off-by: Eric Biggers --- net/dns_resolver/dns_key.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/net/dns_resolver/dns_key.c b/net/dns_resolver/dns_key.c index e1d4d898a007..7c0aae2e512d 100644 --- a/net/dns_resolver/dns_key.c +++ b/net/dns_resolver/dns_key.c @@ -91,9 +91,9 @@ dns_resolver_preparse(struct key_preparsed_payload *prep) next_opt = memchr(opt, '#', end - opt) ?: end; opt_len = next_opt - opt; - if (!opt_len) { - printk(KERN_WARNING - "Empty option to dns_resolver key\n"); + if (opt_len <= 0 || opt_len > 128) { + pr_warn("Invalid option length (%d) for dns_resolver key\n", + opt_len); return -EINVAL; } -- 2.16.2.395.g2e18187dfd-goog