Retry accept() even if accepted connection reports an error (CVE-2025-48367)

In case of accept4() returns an error, we should check errno value and decide if we should retry accept4() without waiting next event loop iteration.

src/anet.c

@@ -787,3 +787,27 @@ int anetIsFifo(char *filepath) {
     if (stat(filepath, &sb) == -1) return 0;
     return S_ISFIFO(sb.st_mode);
 }
+
+/* This function must be called after accept4() fails. It returns 1 if 'err'
+ * indicates accepted connection faced an error, and it's okay to continue
+ * accepting next connection by calling accept4() again. Other errors either
+ * indicate programming errors, e.g. calling accept() on a closed fd or indicate
+ * a resource limit has been reached, e.g. -EMFILE, open fd limit has been
+ * reached. In the latter case, caller might wait until resources are available.
+ * See accept4() documentation for details. */
+int anetAcceptFailureNeedsRetry(int err) {
+    if (err == ECONNABORTED)
+        return 1;
+
+#if defined(__linux__)
+    /* For details, see 'Error Handling' section on
+     * https://man7.org/linux/man-pages/man2/accept.2.html */
+    if (err == ENETDOWN || err == EPROTO || err == ENOPROTOOPT ||
+        err == EHOSTDOWN || err == ENONET || err == EHOSTUNREACH ||
+        err == EOPNOTSUPP || err == ENETUNREACH)
+    {
+        return 1;
+    }
+#endif
+    return 0;
+}

src/anet.h

@@ -53,5 +53,6 @@ int anetPipe(int fds[2], int read_flags, int write_flags);
 int anetSetSockMarkId(char *err, int fd, uint32_t id);
 int anetGetError(int fd);
 int anetIsFifo(char *filepath);
+int anetAcceptFailureNeedsRetry(int err);
 
 #endif

src/cluster_legacy.c

@@ -1253,6 +1253,8 @@ void clusterAcceptHandler(aeEventLoop *el, int fd, void *privdata, int mask) {
     while(max--) {
         cfd = anetTcpAccept(server.neterr, fd, cip, sizeof(cip), &cport);
         if (cfd == ANET_ERR) {
+            if (anetAcceptFailureNeedsRetry(errno))
+                continue;
             if (errno != EWOULDBLOCK)
                 serverLog(LL_VERBOSE,
                     "Error accepting cluster node: %s", server.neterr);

src/socket.c

@@ -308,6 +308,8 @@ static void connSocketAcceptHandler(aeEventLoop *el, int fd, void *privdata, int
     while(max--) {
         cfd = anetTcpAccept(server.neterr, fd, cip, sizeof(cip), &cport);
         if (cfd == ANET_ERR) {
+            if (anetAcceptFailureNeedsRetry(errno))
+                continue;
             if (errno != EWOULDBLOCK)
                 serverLog(LL_WARNING,
                     "Accepting client connection: %s", server.neterr);

src/tls.c

@@ -771,6 +771,8 @@ static void tlsAcceptHandler(aeEventLoop *el, int fd, void *privdata, int mask)
     while(max--) {
         cfd = anetTcpAccept(server.neterr, fd, cip, sizeof(cip), &cport);
         if (cfd == ANET_ERR) {
+            if (anetAcceptFailureNeedsRetry(errno))
+                continue;
             if (errno != EWOULDBLOCK)
                 serverLog(LL_WARNING,
                     "Accepting client connection: %s", server.neterr);

src/unix.c

@@ -102,6 +102,8 @@ static void connUnixAcceptHandler(aeEventLoop *el, int fd, void *privdata, int m
     while(max--) {
         cfd = anetUnixAccept(server.neterr, fd);
         if (cfd == ANET_ERR) {
+            if (anetAcceptFailureNeedsRetry(errno))
+                continue;
             if (errno != EWOULDBLOCK)
                 serverLog(LL_WARNING,
                     "Accepting client connection: %s", server.neterr);