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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , linux-kernel@vger.kernel.org Subject: [PATCH net-next] net: netlink: warn on overwriting extack message Date: Wed, 13 May 2026 22:32:16 +0800 Message-ID: <20260513143219.3327287-1-mmyangfl@gmail.com> X-Mailer: git-send-email 2.53.0 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit When NL_SET_ERR_MSG is called more than once on the same extack, the existing message is silently overwritten. This is hard to detect via static analysis. Emit a rate-limited warning so these cases become visible. Signed-off-by: David Yang --- include/linux/netlink.h | 15 +++++++++++---- 1 file changed, 11 insertions(+), 4 deletions(-) diff --git a/include/linux/netlink.h b/include/linux/netlink.h index 882e9c1b6c1d..f6538304745f 100644 --- a/include/linux/netlink.h +++ b/include/linux/netlink.h @@ -90,6 +90,13 @@ struct netlink_ext_ack { char _msg_buf[NETLINK_MAX_FMTMSG_LEN]; }; +#define __NL_SET_MSG(__extack, __msg) do { \ + if (__extack->_msg) \ + net_warn_ratelimited("overriding extack: %s", \ + __extack->_msg); \ + __extack->_msg = __msg; \ +} while (0) + /* Always use this macro, this allows later putting the * message into a separate section or such for things * like translation or listing all possible messages. @@ -102,7 +109,7 @@ struct netlink_ext_ack { do_trace_netlink_extack(__msg); \ \ if (__extack) \ - __extack->_msg = __msg; \ + __NL_SET_MSG(__extack, __msg); \ } while (0) /* We splice fmt with %s at each end even in the snprintf so that both calls @@ -121,7 +128,7 @@ struct netlink_ext_ack { \ do_trace_netlink_extack(__extack->_msg_buf); \ \ - __extack->_msg = __extack->_msg_buf; \ + __NL_SET_MSG(__extack, __extack->_msg_buf); \ } while (0) #define NL_SET_ERR_MSG_MOD(extack, msg) \ @@ -156,7 +163,7 @@ struct netlink_ext_ack { do_trace_netlink_extack(__msg); \ \ if (__extack) { \ - __extack->_msg = __msg; \ + __NL_SET_MSG(__extack, __msg); \ __extack->bad_attr = (attr); \ __extack->policy = (pol); \ } \ @@ -176,7 +183,7 @@ struct netlink_ext_ack { \ do_trace_netlink_extack(__extack->_msg_buf); \ \ - __extack->_msg = __extack->_msg_buf; \ + __NL_SET_MSG(__extack, __extack->_msg_buf); \ __extack->bad_attr = (attr); \ __extack->policy = (pol); \ } while (0) -- 2.53.0