RDMA/cma: Distinguish between sockaddr_in and sockaddr_in6 by size

Clang can do some aggressive inlining, which provides it with greater
visibility into the sizes of various objects that are passed into
helpers. Specifically, compare_netdev_and_ip() can see through the type
given to the "sa" argument, which means it can generate code for "struct
sockaddr_in" that would have been passed to ipv6_addr_cmp() (that expects
to operate on the larger "struct sockaddr_in6"), which would result in a
compile-time buffer overflow condition detected by memcmp(). Logically,
this state isn't reachable due to the sa_family assignment two callers
above and the check in compare_netdev_and_ip(). Instead, provide a
compile-time check on sizes so the size-mismatched code will be elided
when inlining. Avoids the following warning from Clang:

../include/linux/fortify-string.h:652:4: error: call to '__read_overflow' declared with 'error' attribute: detected read beyond size of object (1st parameter)
                        __read_overflow();
                        ^
note: In function 'cma_netevent_callback'
note:   which inlined function 'node_from_ndev_ip'
1 error generated.

When the underlying object size is not known (e.g. with GCC and older
Clang), the result of __builtin_object_size() is SIZE_MAX, which will also
compile away, leaving the code as it was originally.

Link: https://lore.kernel.org/r/[email protected]
Link: ClangBuiltLinux#1687
Signed-off-by: Kees Cook <[email protected]>
Tested-by: Nathan Chancellor <[email protected]> # build
Signed-off-by: Jason Gunthorpe <[email protected]>

Author: kees

drivers/infiniband/core/cma.c

@@ -479,13 +479,20 @@ static int compare_netdev_and_ip(int ifindex_a, struct sockaddr *sa,
 	if (sa->sa_family != sb->sa_family)
 		return sa->sa_family - sb->sa_family;
 
-	if (sa->sa_family == AF_INET)
-		return memcmp((char *)&((struct sockaddr_in *)sa)->sin_addr,
-			      (char *)&((struct sockaddr_in *)sb)->sin_addr,
+	if (sa->sa_family == AF_INET &&
+	    __builtin_object_size(sa, 0) >= sizeof(struct sockaddr_in)) {
+		return memcmp(&((struct sockaddr_in *)sa)->sin_addr,
+			      &((struct sockaddr_in *)sb)->sin_addr,
 			      sizeof(((struct sockaddr_in *)sa)->sin_addr));
+	}
+
+	if (sa->sa_family == AF_INET6 &&
+	    __builtin_object_size(sa, 0) >= sizeof(struct sockaddr_in6)) {
+		return ipv6_addr_cmp(&((struct sockaddr_in6 *)sa)->sin6_addr,
+				     &((struct sockaddr_in6 *)sb)->sin6_addr);
+	}
 
-	return ipv6_addr_cmp(&((struct sockaddr_in6 *)sa)->sin6_addr,
-			     &((struct sockaddr_in6 *)sb)->sin6_addr);
+	return -1;
 }
 
 static int cma_add_id_to_tree(struct rdma_id_private *node_id_priv)