fsck: do not reuse child_process structs

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->args or child->env_array, they are cleared after
   finish_command()

 - likewise, start_command() may point child->argv at child->args->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 <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: peff

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))