fsck: do not reuse child_process structs

peff · gitster · commit 4d0984bebc5f · 2018-11-13T14:22:02.000+09:00
The run-command API makes no promises about what is left in a struct
child_process after a command finishes, and it's not safe to simply
reuse it again for a similar command. In particular:

 - if you use child-&gt;args or child-&gt;env_array, they are cleared after
   finish_command()

 - likewise, start_command() may point child-&gt;argv at child-&gt;args-&gt;argv;
   reusing that would lead to accessing freed memory

 - the in/out/err may hold pipe descriptors from the previous run

These two calls are _probably_ OK because they do not use any of those
features. But it's only by chance, and may break in the future; let's
reinitialize our struct for each program we run.

Signed-off-by: Jeff King &lt;peff@peff.net&gt;
Signed-off-by: Junio C Hamano &lt;gitster@pobox.com&gt;
diff --git a/builtin/fsck.c b/builtin/fsck.c
@@ -841,6 +841,9 @@ int cmd_fsck(int argc, const char **argv, const char *prefix)
 
 		prepare_alt_odb(the_repository);
 		for (alt =  the_repository->objects->alt_odb_list; alt; alt = alt->next) {
+			child_process_init(&commit_graph_verify);
+			commit_graph_verify.argv = verify_argv;
+			commit_graph_verify.git_cmd = 1;
 			verify_argv[2] = "--object-dir";
 			verify_argv[3] = alt->path;
 			if (run_command(&commit_graph_verify))
@@ -859,6 +862,9 @@ int cmd_fsck(int argc, const char **argv, const char *prefix)
 
 		prepare_alt_odb(the_repository);
 		for (alt =  the_repository->objects->alt_odb_list; alt; alt = alt->next) {
+			child_process_init(&midx_verify);
+			midx_verify.argv = midx_argv;
+			midx_verify.git_cmd = 1;
 			midx_argv[2] = "--object-dir";
 			midx_argv[3] = alt->path;
 			if (run_command(&midx_verify))
