From 9c438d7a3a52dcc2b9ed095cb87d3a5e83cf7e60 Mon Sep 17 00:00:00 2001 From: Eric Biggers Date: Tue, 17 Apr 2018 12:07:06 -0700 Subject: KEYS: DNS: limit the length of option strings 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. Also ratelimit the printks. 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]") Signed-off-by: Eric Biggers Signed-off-by: David S. Miller --- net/dns_resolver/dns_key.c | 12 +++++------- 1 file changed, 5 insertions(+), 7 deletions(-) (limited to 'net/dns_resolver') diff --git a/net/dns_resolver/dns_key.c b/net/dns_resolver/dns_key.c index 8396705deffc..40c851693f77 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_ratelimited("Invalid option length (%d) for dns_resolver key\n", + opt_len); return -EINVAL; } @@ -127,10 +127,8 @@ dns_resolver_preparse(struct key_preparsed_payload *prep) } bad_option_value: - printk(KERN_WARNING - "Option '%*.*s' to dns_resolver key:" - " bad/missing value\n", - opt_nlen, opt_nlen, opt); + pr_warn_ratelimited("Option '%*.*s' to dns_resolver key: bad/missing value\n", + opt_nlen, opt_nlen, opt); return -EINVAL; } while (opt = next_opt + 1, opt < end); } -- cgit v1.2.3-59-g8ed1b