[Dnsmasq-discuss] [PATCH] Fix buffer overflow in TCP requests

[Frank]

Hello,

This patch fixes a buffer overflow in TCP requests. Since the read is not actually being retried, the byte written by the child can be left in the pipe. When that happens, cache_recv_insert() reads the length of the name, which is now multiplied by 256 due to the extra 0 byte (8 bit shift) and results in daemon->namebuff being overflowed. Namebuff is immediately before the daemon struct in memory so it ends up corrupting the beginning of the daemon struct.

diff --git a/src/dnsmasq.c b/src/dnsmasq.c
index 6481de8..457dea3 100644
--- a/src/dnsmasq.c
+++ b/src/dnsmasq.c
@@ -1887,7 +1887,7 @@ static void check_dns_listeners(time_t now)
                           single byte comes back up the pipe, which
                           is sent by the child after it has closed the
                           netlink socket. */
-                       retry_send(read(pipefd[0], &a, 1));
+                       while (retry_send(read(pipefd[0], &a, 1)));
 #endif
                        break;
                      }
@@ -1928,7 +1928,7 @@ static void check_dns_listeners(time_t now)
 #ifdef HAVE_LINUX_NETWORK
                  /* See comment above re netlink socket. */
                  close(daemon->netlinkfd);
-                 retry_send(write(pipefd[1], &a, 1));
+                 while (retry_send(write(pipefd[1], &a, 1)));
 #endif
                }

Frank