n-dhcp4/packet: avoid compiler warning in n_dhcp4_c_socket_packet_recv()

gcc-10.2.1-1.fc32 with optimizations and LTO enabled can think that "len"
is uninitialized. Let packet_recv_udp() always set the length.

  ../src/n-dhcp4-socket.c: In function ‘n_dhcp4_c_socket_packet_recv.constprop’:
  ../src/n-dhcp4-incoming.c:210:29: error: ‘len’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
    210 |         incoming->n_message = n_raw;
        |                             ^
  ../src/n-dhcp4-socket.c:558:16: note: ‘len’ was declared here
    558 |         size_t len;
        |                ^

https://github.com/nettools/n-dhcp4/commit/142eedcfc332e52f3d3fdfa557be4d77a934e62d

1 files changed, 2 insertions, 10 deletions

diff --git a/shared/n-dhcp4/src/util/packet.c b/shared/n-dhcp4/src/util/packet.c
index fb0313abe7..ef18b0b464 100644
--- a/shared/n-dhcp4/src/util/packet.c
+++ b/shared/n-dhcp4/src/util/packet.c
@@ -293,6 +293,8 @@ int packet_recvfrom_udp(int sockfd,
         ssize_t pktlen;
         size_t hdrlen;
 
+        *n_transmittedp = 0;
+
         /* Peek packet to obtain the real IP header length */
         pktlen = recv(sockfd, &ip_hdr.hdr, sizeof(ip_hdr.hdr), MSG_PEEK);
         if (pktlen < 0)
@@ -304,7 +306,6 @@ int packet_recvfrom_udp(int sockfd,
                  * discard it.
                  */
                 recv(sockfd, NULL, 0, 0);
-                *n_transmittedp = 0;
                 return 0;
         }
 
@@ -313,7 +314,6 @@ int packet_recvfrom_udp(int sockfd,
                  * This is not an IPv4 packet, discard it.
                  */
                 recv(sockfd, NULL, 0, 0);
-                *n_transmittedp = 0;
                 return 0;
         }
 
@@ -324,7 +324,6 @@ int packet_recvfrom_udp(int sockfd,
                  * header length, discard the packet.
                  */
                 recv(sockfd, NULL, 0, 0);
-                *n_transmittedp = 0;
                 return 0;
         }
 
@@ -354,7 +353,6 @@ int packet_recvfrom_udp(int sockfd,
                  * provided too small a buffer. In both cases, we simply drop
                  * the packet.
                  */
-                *n_transmittedp = 0;
                 return 0;
         }
 
@@ -366,14 +364,12 @@ int packet_recvfrom_udp(int sockfd,
                  * The packet is too small to even contain an entire UDP
                  * header, so discard it entirely.
                  */
-                *n_transmittedp = 0;
                 return 0;
         } else if ((size_t)pktlen < hdrlen + ntohs(udp_hdr.len)) {
                 /*
                  * The UDP header specified a longer length than the returned
                  * packet, so discard it entirely.
                  */
-                *n_transmittedp = 0;
                 return 0;
         }
 
@@ -386,13 +382,10 @@ int packet_recvfrom_udp(int sockfd,
         /* IP */
 
         if (ip_hdr.hdr.protocol != IPPROTO_UDP) {
-                *n_transmittedp = 0;
                 return 0; /* not a UDP packet, discard it */
         } else if (ip_hdr.hdr.frag_off & htons(IP_MF | IP_OFFMASK)) {
-                *n_transmittedp = 0;
                 return 0; /* fragmented packet, discard it */
         } else if (checksum && packet_internet_checksum(ip_hdr.data, hdrlen)) {
-                *n_transmittedp = 0;
                 return 0; /* invalid checksum, discard it */
         }
 
@@ -411,7 +404,6 @@ int packet_recvfrom_udp(int sockfd,
                                                 buf,
                                                 pktlen,
                                                 udp_hdr.check)) {
-                        *n_transmittedp = 0;
                         return 0;
                }
         }