libsubcmd: Fix null intersection case in exclude_cmds()

When there is no exclusion occurring from the cmds list - for example -
cmds contains ["read-vdso32"] and excludes contains ["archive"] - the
main loop completes with ci == cj == 0. In the original code the loop
processing the remaining elements in the list was conditional:

    if (ci != cj) { ...}

So we end up in the assertion loop since ci < cmds->cnt and we
incorrectly try to assert the list elements to be NULL and fail with
the following error

   help.c:104: exclude_cmds: Assertion `cmds->names[ci] == NULL' failed.

Fix this by moving the if (ci != cj) check inside of a broader loop.
If ci != cj, left shift the list elements, as before, and then
unconditionally advance the ci and cj indicies which also covers the
ci == cj case.

Fixes: 1fdf938168c4d26f ("perf tools: Fix use-after-free in help_unknown_cmd()")
Reviewed-by: Guilherme Amadio <amadio@gentoo.org>
Signed-off-by: Sri Jayaramappa <sjayaram@akamai.com>
Tested-by: Guilherme Amadio <amadio@gentoo.org>
Tested-by: Ian Rogers <irogers@google.com>
Cc: Joshua Hunt <johunt@akamai.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20251202213632.2873731-1-sjayaram@akamai.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

diff --git a/tools/lib/subcmd/help.c b/tools/lib/subcmd/help.c
index ddaeb4eb3e2497f40a728f58656cf7a78bb37ebd..db94aa685b73b8e1ae2621f00615825cac1c4114 100644 (file)
--- a/tools/lib/subcmd/help.c
+++ b/tools/lib/subcmd/help.c
@@ -97,11 +97,13 @@ void exclude_cmds(struct cmdnames *cmds, struct cmdnames *excludes)
                        ei++;
                }
        }
-       if (ci != cj) {
-               while (ci < cmds->cnt) {
-                       cmds->names[cj++] = cmds->names[ci];
-                       cmds->names[ci++] = NULL;
+       while (ci < cmds->cnt) {
+               if (ci != cj) {
+                       cmds->names[cj] = cmds->names[ci];
+                       cmds->names[ci] = NULL;
                }
+               ci++;
+               cj++;
        }
        for (ci = cj; ci < cmds->cnt; ci++)
                assert(cmds->names[ci] == NULL);