Hey Simon,
another patch fixing a small memcheck error reported during Pi-hole
testing. The error is caused in send_from() (forward.c) by handing a
partially uninitialized stack variable to sendmsg() when nowild == false.
Full error output (example):
==1052839== Syscall param sendmsg(msg.msg_control) points to
uninitialised byte(s)
==1052839== at 0x4B7199D: __libc_sendmsg (sendmsg.c:28)
==1052839== by 0x4B7199D: sendmsg (sendmsg.c:25)
==1052839== by 0x21EADB: send_from (forward.c:101)
==1052839== by 0x222551: receive_query (forward.c:1988)
==1052839== by 0x20FD6A: check_dns_listeners (dnsmasq.c:1886)
==1052839== by 0x2120EF: main (dnsmasq.c:1278)
==1052839== Location 0x1fff000098is 24bytes inside local var "control_u"
==1052839== declared at forward.c:49, in frame #1of thread 1
==1052839== Uninitialised value was created by a stack allocation
==1052839== at 0x21EA11: send_from (forward.c:38)
Note that the line-numbers are not necessarily 100% accurate. We have
not noticed any abnormal behavior, however, fixing this reported error
is easy enough.
Best,
Dominik
From fd37817ec8ae02c8c4d449df339d179f767caba4 Mon Sep 17 00:00:00 2001
From: Dominik Derigs <dl...@dl6er.de>
Date: Sat, 27 Jul 2024 11:13:49 +0200
Subject: [PATCH] Fix memcheck errors like "Syscall param
sendmsg(msg.msg_control) points to uninitialised byte(s)"
Signed-off-by: Dominik Derigs <dl...@dl6er.de>
---
src/forward.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/src/forward.c b/src/forward.c
index 10e7496..004935e 100644
--- a/src/forward.c
+++ b/src/forward.c
@@ -35,7 +35,7 @@ int send_from(int fd, int nowild, char *packet, size_t len,
union mysockaddr *to, union all_addr *source,
unsigned int iface)
{
- struct msghdr msg;
+ struct msghdr msg = { 0 };
struct iovec iov[1];
union {
struct cmsghdr align; /* this ensures alignment */
@@ -45,7 +45,7 @@ int send_from(int fd, int nowild, char *packet, size_t len,
char control[CMSG_SPACE(sizeof(struct in_addr))];
#endif
char control6[CMSG_SPACE(sizeof(struct in6_pktinfo))];
- } control_u;
+ } control_u = { 0 };
iov[0].iov_base = packet;
iov[0].iov_len = len;
--
2.34.1
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