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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Shuah Khan Cc: Kuniyuki Iwashima , netdev@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, Chaithanya Lagisetty Subject: [PATCH] selftests: net: ipmr: Avoid memcpy() from NULL in nl_add_rtattr() Date: Tue, 1 Sep 2026 07:13:53 +0000 Message-ID: <20260901071353.3302900-1-nagachaithanya9911@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit nl_add_rtattr() unconditionally does memcpy(RTA_DATA(rta), data, len). For zero-length attributes the callers pass data == NULL and len == 0, for example the RTA_PREFSRC attribute added for proxy MFC entries: if (mfc_attr->proxy) rta = nl_add_rtattr(nlmsg, rta, RTA_PREFSRC, NULL, 0); Passing a NULL pointer to memcpy() is undefined behaviour even when the length is zero, because its source parameter is marked __attribute__((nonnull)); it is flagged by fortify/-Wnonnull. Only call memcpy() when len is non-zero. Fixes: 05068eaa67b2 ("selftest: net: Add basic functionality tests for ipmr.") Signed-off-by: Chaithanya Lagisetty --- tools/testing/selftests/net/forwarding/ipmr.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/tools/testing/selftests/net/forwarding/ipmr.c b/tools/testing/selftests/net/forwarding/ipmr.c index 9cd9f70de132..d3e26341821c 100644 --- a/tools/testing/selftests/net/forwarding/ipmr.c +++ b/tools/testing/selftests/net/forwarding/ipmr.c @@ -120,7 +120,8 @@ static struct rtattr *nl_add_rtattr(struct nlmsghdr *nlmsg, struct rtattr *rta, rta->rta_type = type; rta->rta_len = RTA_LENGTH(len); - memcpy(RTA_DATA(rta), data, len); + if (len) + memcpy(RTA_DATA(rta), data, len); nlmsg->nlmsg_len += NLMSG_ALIGN(rta->rta_len); -- 2.43.0