[PATCH v2] lib subcmd: Avoid segv/use-after-free when commands aren't excluded

[Ian Rogers <irogers@google.com>]

The array shortening may perform unnecessary array copies. Before
commit 657a3efee43a ("lib subcmd: Avoid memory leak in exclude_cmds")
this was benign, but afterwards this could lead to a segv.

Fixes: 657a3efee43a ("lib subcmd: Avoid memory leak in exclude_cmds")
Signed-off-by: Ian Rogers <irogers@google.com>
---
 tools/lib/subcmd/help.c | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/tools/lib/subcmd/help.c b/tools/lib/subcmd/help.c
index 67a8d6b740ea..adfbae27dc36 100644
--- a/tools/lib/subcmd/help.c
+++ b/tools/lib/subcmd/help.c
@@ -68,8 +68,13 @@ void exclude_cmds(struct cmdnames *cmds, struct cmdnames *excludes)
 	while (ci < cmds->cnt && ei < excludes->cnt) {
 		cmp = strcmp(cmds->names[ci]->name, excludes->names[ei]->name);
 		if (cmp < 0) {
-			zfree(&cmds->names[cj]);
-			cmds->names[cj++] = cmds->names[ci++];
+			if (ci == cj) {
+				ci++;
+				cj++;
+			} else {
+				zfree(&cmds->names[cj]);
+				cmds->names[cj++] = cmds->names[ci++];
+			}
 		} else if (cmp == 0) {
 			ci++;
 			ei++;
@@ -77,10 +82,11 @@ void exclude_cmds(struct cmdnames *cmds, struct cmdnames *excludes)
 			ei++;
 		}
 	}
-
-	while (ci < cmds->cnt) {
-		zfree(&cmds->names[cj]);
-		cmds->names[cj++] = cmds->names[ci++];
+	if (ci != cj) {
+		while (ci < cmds->cnt) {
+			zfree(&cmds->names[cj]);
+			cmds->names[cj++] = cmds->names[ci++];
+		}
 	}
 	for (ci = cj; ci < cmds->cnt; ci++)
 		zfree(&cmds->names[ci]);
-- 
2.41.0.390.g38632f3daf-goog