Merge pull request #27253 from yuwata/cmsg-find-and-copy-data

socket-util: introduce CMSG_FIND_AND_COPY_DATA()

src/basic/socket-util.c

@@ -1171,6 +1171,24 @@ struct cmsghdr* cmsg_find(struct msghdr *mh, int level, int type, socklen_t leng
         return NULL;
 }
 
+void* cmsg_find_and_copy_data(struct msghdr *mh, int level, int type, void *buf, size_t buf_len) {
+        struct cmsghdr *cmsg;
+
+        assert(mh);
+        assert(buf);
+        assert(buf_len > 0);
+
+        /* This is similar to cmsg_find_data(), but copy the found data to buf. This should be typically used
+         * when reading possibly unaligned data such as timestamp, as time_t is 64bit and size_t is 32bit on
+         * RISCV32. See issue #27241. */
+
+        cmsg = cmsg_find(mh, level, type, CMSG_LEN(buf_len));
+        if (!cmsg)
+                return NULL;
+
+        return memcpy_safe(buf, CMSG_DATA(cmsg), buf_len);
+}
+
 int socket_ioctl_fd(void) {
         int fd;
 

src/basic/socket-util.h

@@ -183,17 +183,22 @@ int flush_accept(int fd);
  * riscv32. */
 #define CMSG_TYPED_DATA(cmsg, type)                                     \
         ({                                                              \
-                struct cmsghdr *_cmsg = cmsg;                           \
-                assert_cc(__alignof__(type) <= __alignof__(struct cmsghdr)); \
+                struct cmsghdr *_cmsg = (cmsg);                         \
+                assert_cc(alignof(type) <= alignof(struct cmsghdr));    \
                 _cmsg ? CAST_ALIGN_PTR(type, CMSG_DATA(_cmsg)) : (type*) NULL; \
         })
 
 struct cmsghdr* cmsg_find(struct msghdr *mh, int level, int type, socklen_t length);
+void* cmsg_find_and_copy_data(struct msghdr *mh, int level, int type, void *buf, size_t buf_len);
 
 /* Type-safe, dereferencing version of cmsg_find() */
 #define CMSG_FIND_DATA(mh, level, type, ctype)                          \
         CMSG_TYPED_DATA(cmsg_find(mh, level, type, CMSG_LEN(sizeof(ctype))), ctype)
 
+/* Type-safe version of cmsg_find_and_copy_data() */
+#define CMSG_FIND_AND_COPY_DATA(mh, level, type, ctype)             \
+        (ctype*) cmsg_find_and_copy_data(mh, level, type, &(ctype){}, sizeof(ctype))
+
 /* Resolves to a type that can carry cmsghdr structures. Make sure things are properly aligned, i.e. the type
  * itself is placed properly in memory and the size is also aligned to what's appropriate for "cmsghdr"
  * structures. */