From bbd403a7ab3810fe82ecd1d6ebca9fc34d68126a Mon Sep 17 00:00:00 2001 From: Maxim Dounin Date: Tue, 25 May 2021 15:17:41 +0300 Subject: [PATCH] Resolver: fixed label types handling in ngx_resolver_copy(). Previously, anything with any of the two high bits set were interpreted as compression pointers. This is incorrect, as RFC 1035 clearly states that "The 10 and 01 combinations are reserved for future use". Further, the 01 combination is actually allocated for EDNS extended label type (see RFC 2671 and RFC 6891), not really used though. Fix is to reject unrecognized label types rather than misinterpreting them as compression pointers. --- src/core/ngx_resolver.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/src/core/ngx_resolver.c b/src/core/ngx_resolver.c index 9b1317234..12dab09ea 100644 --- a/src/core/ngx_resolver.c +++ b/src/core/ngx_resolver.c @@ -3958,6 +3958,11 @@ ngx_resolver_copy(ngx_resolver_t *r, ngx_str_t *name, u_char *buf, u_char *src, } if (n & 0xc0) { + if ((n & 0xc0) != 0xc0) { + err = "invalid label type in DNS response"; + goto invalid; + } + if (p >= last) { err = "name is out of DNS response"; goto invalid;