Subject: avahi_dns_packet_consume_uint32: fix potential undefined behavior
From: traffic-millions <[email-masked]>
Date: Tue, 3 Mar 2020 11:15:48 +0800

avahi_dns_packet_consume_uint32 left shifts uint8_t values by 8, 16 and 24 bits to combine them into a 32-bit value. This produces an undefined behavior warning with gcc -fsanitize when fed input values of 128 or 255 however in testing no actual unexpected behavior occurs in practice and the 32-bit uint32_t is always correctly produced as the final value is immediately stored into a uint32_t and the compiler appears to handle this "correctly".

Cast the intermediate values to uint32_t to prevent this warning and ensure the intended result is explicit.

Closes: #267
Closes: #268
Reference: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=19304
Origin: upstream, 0.9, commit:b897ca43ac100d326d118e5877da710eb7f836f9
---
 avahi-core/dns.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/avahi-core/dns.c
+++ b/avahi-core/dns.c
@@ -455,7 +455,7 @@ int avahi_dns_packet_consume_uint32(Avah
         return -1;
 
     d = (uint8_t*) (AVAHI_DNS_PACKET_DATA(p) + p->rindex);
-    *ret_v = (d[0] << 24) | (d[1] << 16) | (d[2] << 8) | d[3];
+    *ret_v = ((uint32_t)d[0] << 24) | ((uint32_t)d[1] << 16) | ((uint32_t)d[2] << 8) | (uint32_t)d[3];
     p->rindex += sizeof(uint32_t);
 
     return 0;