2023-06-26 22:46:04

by Ian Rogers

Subject: [PATCH v1] lib subcmd: Avoid use-after-free when no commands are excluded

The array shortening may be an unnecessary array copy. 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 <[email protected]>
---
tools/lib/subcmd/help.c | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/tools/lib/subcmd/help.c b/tools/lib/subcmd/help.c
index 67a8d6b740ea..b59ca17e406d 100644
--- a/tools/lib/subcmd/help.c
+++ b/tools/lib/subcmd/help.c
@@ -77,10 +77,11 @@ 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]);
--
2.41.0.162.gfafddb0af9-goog

2023-07-01 19:20:28

by Namhyung Kim

Subject: Re: [PATCH v1] lib subcmd: Avoid use-after-free when no commands are excluded

On Mon, Jun 26, 2023 at 3:22 PM Ian Rogers <[email protected]> wrote:
>
> The array shortening may be an unnecessary array copy. 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 <[email protected]>
> ---
> tools/lib/subcmd/help.c | 9 +++++----
> 1 file changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/tools/lib/subcmd/help.c b/tools/lib/subcmd/help.c
> index 67a8d6b740ea..b59ca17e406d 100644
> --- a/tools/lib/subcmd/help.c
> +++ b/tools/lib/subcmd/help.c
> @@ -77,10 +77,11 @@ 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++];

I'm not sure I'm following the logic in this function well
but it seems we also need to check the same thing
in the above loop - if (cmp < 0).

Thanks,
Namhyung


> + }
> }
> for (ci = cj; ci < cmds->cnt; ci++)
> zfree(&cmds->names[ci]);
> --
> 2.41.0.162.gfafddb0af9-goog
>