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[176.103.220.4]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-4606f2b0d70sm53660f8f.19.2026.06.11.16.05.25 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 11 Jun 2026 16:05:25 -0700 (PDT) From: Stefano Brivio To: Jon Maloy Subject: Re: [PATCH v2] udp: Provide dummy iov in udp_peek_addr() to avoid Coverity warning Message-ID: <20260612010524.3254219b@elisabeth> In-Reply-To: <20260608005026.515574-1-jmaloy@redhat.com> References: <20260608005026.515574-1-jmaloy@redhat.com> Organization: Red Hat X-Mailer: Claws Mail 4.2.0 (GTK 3.24.49; x86_64-pc-linux-gnu) MIME-Version: 1.0 Date: Fri, 12 Jun 2026 01:05:25 +0200 (CEST) X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: 5nQdGlsNB8o9rd6beNB2NbVjZC21mBqnvHyo5U9uUy8_1781219127 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Message-ID-Hash: MDIEOOHTPDRAMHYIP32OWXAVZS2HF4RL X-Message-ID-Hash: MDIEOOHTPDRAMHYIP32OWXAVZS2HF4RL X-MailFrom: sbrivio@redhat.com X-Mailman-Rule-Misses: dmarc-mitigation; no-senders; approved; emergency; loop; banned-address; member-moderation; nonmember-moderation; administrivia; implicit-dest; max-recipients; max-size; news-moderation; no-subject; digests; suspicious-header CC: david@gibson.dropbear.id.au, passt-dev@passt.top X-Mailman-Version: 3.3.8 Precedence: list List-Id: Development discussion and patches for passt Archived-At: Archived-At: List-Archive: List-Archive: List-Help: List-Owner: List-Post: List-Subscribe: List-Unsubscribe: On Sun, 7 Jun 2026 20:50:26 -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 > > ---- > v2: - Make the dummy iov conditional on an ANALYZER macro, so it has > zero runtime cost in production builds. As I mentioned offline, I'd rather go with v1, because a macro that's not enabled / seen by any static checker isn't really convenient. And I'll take care of reporting this to Coverity. Just one detail, regardless of that: > - 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, ...can't we pass 0 instead? What happens? That looks like less potential for overhead in the sense of a possible copy_to_user() that we don't want to trigger. > +#endif /* ANALYZER */ > .msg_control = cmsg, > .msg_controllen = sizeof(cmsg), > }; -- Stefano