[PATCH v2] udp: Provide dummy iov in udp_peek_addr() to avoid Coverity warning
udp_peek_addr() initialises struct msghdr without setting msg_iov,
leaving it implicitly NULL. Coverity flags this as FORWARD_NULL,
believing recvmsg() will dereference the NULL pointer.
In practice, msg_iovlen being zero means the kernel never touches
msg_iov, so the warning is a false positive. We now provide a
one-byte dummy iov to make msg_iov non-NULL, hence suppressing this
warning without changing the function's behaviour.
Signed-off-by: Jon Maloy
On Sun, Jun 07, 2026 at 08:50:26PM -0400, Jon Maloy wrote:
udp_peek_addr() initialises struct msghdr without setting msg_iov, leaving it implicitly NULL. Coverity flags this as FORWARD_NULL, believing recvmsg() will dereference the NULL pointer.
In practice, msg_iovlen being zero means the kernel never touches msg_iov, so the warning is a false positive. We now provide a one-byte dummy iov to make msg_iov non-NULL, hence suppressing this warning without changing the function's behaviour.
Signed-off-by: Jon Maloy
Following on from our discussion yesterday. Although this is based on my suggestion, I'm now inclined to believe v1 is marginally less ugly. Fwiw, I double checked the code and can now confirm that this is only called for packets arriving on a "listening" socket, rather than a flow-specific socket. Typically that will only be once, or at worst a handful of times, per flow.
---- v2: - Make the dummy iov conditional on an ANALYZER macro, so it has zero runtime cost in production builds. - Add a new 'analyzer' Makefile target (similar to 'valgrind') that defines ANALYZER via CPPFLAGS for use with static analysis builds. --- Makefile | 3 +++ udp.c | 11 +++++++++++ 2 files changed, 14 insertions(+)
diff --git a/Makefile b/Makefile index 0a0a60b0..4dcf4cd1 100644 --- a/Makefile +++ b/Makefile @@ -122,6 +122,9 @@ passt-repair: $(PASST_REPAIR_SRCS) $(PASST_REPAIR_HEADERS) seccomp_repair.h pesto: BASE_CPPFLAGS += -DPESTO pesto: $(PESTO_SRCS) $(PESTO_HEADERS) seccomp_pesto.h
+analyzer: BASE_CPPFLAGS += -DANALYZER +analyzer: all + valgrind: EXTRA_SYSCALLS += rt_sigprocmask rt_sigtimedwait rt_sigaction \ rt_sigreturn getpid gettid kill clock_gettime \ mmap|mmap2 munmap open unlink gettimeofday futex \ diff --git a/udp.c b/udp.c index c28d6ee2..36c8c070 100644 --- a/udp.c +++ b/udp.c @@ -734,9 +734,20 @@ static int udp_peek_addr(int s, union sockaddr_inany *src, { char sastr[SOCKADDR_STRLEN], dstr[INANY_ADDRSTRLEN]; char cmsg[PKTINFO_SPACE]; +#ifdef ANALYZER + char dummy; + struct iovec iov = { + .iov_base = &dummy, + .iov_len = sizeof(dummy), + }; +#endif /* ANALYZER */ struct msghdr msg = { .msg_name = src, .msg_namelen = sizeof(*src), +#ifdef ANALYZER + .msg_iov = &iov, + .msg_iovlen = 1, +#endif /* ANALYZER */ .msg_control = cmsg, .msg_controllen = sizeof(cmsg), }; -- 2.52.0
-- David Gibson (he or they) | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you, not the other way | around. http://www.ozlabs.org/~dgibson
participants (2)
-
David Gibson
-
Jon Maloy