tools: bpftool: fix potential NULL pointer dereference in do_load

This patch fixes a possible null pointer dereference in
do_load, detected by the semantic patch deref_null.cocci,
with the following warning:

./tools/bpf/bpftool/prog.c:1021:23-25: ERROR: map_replace is NULL but dereferenced.

The following code has potential null pointer references:
881             map_replace = reallocarray(map_replace, old_map_fds + 1,
882                                        sizeof(*map_replace));
883             if (!map_replace) {
884                     p_err("mem alloc failed");
885                     goto err_free_reuse_maps;
886             }

...
1019 err_free_reuse_maps:
1020         for (i = 0; i < old_map_fds; i++)
1021                 close(map_replace[i].fd);
1022         free(map_replace);

Fixes: 3ff5a4dc5d89 ("tools: bpftool: allow reuse of maps with bpftool prog load")
Co-developed-by: Wen Yang <wen.yang99@zte.com.cn>
Signed-off-by: Wen Yang <wen.yang99@zte.com.cn>
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

1 files changed, 7 insertions, 3 deletions

diff --git a/tools/bpf/bpftool/prog.c b/tools/bpf/bpftool/prog.c
index 9785244acc7b..ccee180dfb76 100644
--- a/tools/bpf/bpftool/prog.c
+++ b/tools/bpf/bpftool/prog.c
@@ -844,6 +844,7 @@ static int do_load(int argc, char **argv)
                         }
                         NEXT_ARG();
                 } else if (is_prefix(*argv, "map")) {
+                        void *new_map_replace;
                         char *endptr, *name;
                         int fd;
 
@@ -877,12 +878,15 @@ static int do_load(int argc, char **argv)
                         if (fd < 0)
                                 goto err_free_reuse_maps;
 
-                        map_replace = reallocarray(map_replace, old_map_fds + 1,
-                                                   sizeof(*map_replace));
-                        if (!map_replace) {
+                        new_map_replace = reallocarray(map_replace,
+                                                       old_map_fds + 1,
+                                                       sizeof(*map_replace));
+                        if (!new_map_replace) {
                                 p_err("mem alloc failed");
                                 goto err_free_reuse_maps;
                         }
+                        map_replace = new_map_replace;
+
                         map_replace[old_map_fds].idx = idx;
                         map_replace[old_map_fds].name = name;
                         map_replace[old_map_fds].fd = fd;