linux-kernel - Re: [PATCH bpf-next v2 2/2] bpftool: Fix UAF in get_delegate

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Message-ID: <CAEf4BzY3CiVLce-pB9yevsUqFZexbno+AX1j4mGYN1G+JVO+pA@mail.gmail.com>
Date: Wed, 17 Sep 2025 14:00:04 -0700
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Quentin Monnet <qmo@...nel.org>
Cc: Tao Chen <chen.dylane@...ux.dev>, ast@...nel.org, daniel@...earbox.net, 
	andrii@...nel.org, martin.lau@...ux.dev, eddyz87@...il.com, song@...nel.org, 
	yonghong.song@...ux.dev, john.fastabend@...il.com, kpsingh@...nel.org, 
	sdf@...ichev.me, haoluo@...gle.com, jolsa@...nel.org, bpf@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next v2 2/2] bpftool: Fix UAF in get_delegate_value

On Wed, Sep 17, 2025 at 9:30 AM Quentin Monnet <qmo@...nel.org> wrote:
>
> 2025-09-17 11:47 UTC+0800 ~ Tao Chen <chen.dylane@...ux.dev>
> > The return value ret pointer is pointing opts_copy, but opts_copy
> > gets freed in get_delegate_value before return, fix this by free
> > the mntent->mnt_opts strdup memory after show delegate value.
> >
> > Fixes: 2d812311c2b2 ("bpftool: Add bpf_token show")
> > Signed-off-by: Tao Chen <chen.dylane@...ux.dev>
> > ---
> >  tools/bpf/bpftool/token.c | 75 +++++++++++++++++----------------------
> >  1 file changed, 33 insertions(+), 42 deletions(-)
> >
> > diff --git a/tools/bpf/bpftool/token.c b/tools/bpf/bpftool/token.c
> > index 82b829e44c8..05bc76c7276 100644
> > --- a/tools/bpf/bpftool/token.c
> > +++ b/tools/bpf/bpftool/token.c
> > @@ -28,15 +28,14 @@ static bool has_delegate_options(const char *mnt_ops)
> >              strstr(mnt_ops, "delegate_attachs");
> >  }
> >
> > -static char *get_delegate_value(const char *opts, const char *key)
> > +static char *get_delegate_value(char *opts, const char *key)
> >  {
> >       char *token, *rest, *ret = NULL;
> > -     char *opts_copy = strdup(opts);
> >
> > -     if (!opts_copy)
> > +     if (!opts)
> >               return NULL;
> >
> > -     for (token = strtok_r(opts_copy, ",", &rest); token;
> > +     for (token = strtok_r(opts, ",", &rest); token;
> >                       token = strtok_r(NULL, ",", &rest)) {
> >               if (strncmp(token, key, strlen(key)) == 0 &&
> >                   token[strlen(key)] == '=') {
> > @@ -44,24 +43,19 @@ static char *get_delegate_value(const char *opts, const char *key)
> >                       break;
> >               }
> >       }
> > -     free(opts_copy);
> >
> >       return ret;
> >  }
> >
> > -static void print_items_per_line(const char *input, int items_per_line)
> > +static void print_items_per_line(char *input, int items_per_line)
> >  {
> > -     char *str, *rest, *strs;
> > +     char *str, *rest;
> >       int cnt = 0;
> >
> >       if (!input)
> >               return;
> >
> > -     strs = strdup(input);
> > -     if (!strs)
> > -             return;
> > -
> > -     for (str = strtok_r(strs, ":", &rest); str;
> > +     for (str = strtok_r(input, ":", &rest); str;
> >                       str = strtok_r(NULL, ":", &rest)) {
> >               if (cnt % items_per_line == 0)
> >                       printf("\n\t  ");
> > @@ -69,38 +63,39 @@ static void print_items_per_line(const char *input, int items_per_line)
> >               printf("%-20s", str);
> >               cnt++;
> >       }
> > -
> > -     free(strs);
> >  }
> >
> > +#define PRINT_DELEGATE_OPT(opt_name) do {            \
> > +     char *opts, *value;                             \
> > +     opts = strdup(mntent->mnt_opts);                \
> > +     value = get_delegate_value(opts, opt_name);     \
> > +     print_items_per_line(value, ITEMS_PER_LINE);    \
> > +     free(opts);                                     \
> > +} while (0)
>
>
> Thanks! The fix looks OK to me, but why do you need to have
> PRINT_DELEGATE_OPT*() as macros? Can't you just use functions instead?

right, function or just a loop, that will allow to also avoid
repeating jsonw_name or printf calls:

struct { const char *header, key; } sets = {
    {"allowed_cmds", "delegate_cmds"},
    {"allowed_maps", "delegate_maps"},
    ...
};

for (i = 0; i < ARRAY_SIZE(sets); i++) {
    ... use sets[i].header and sets[i].key ...
}

pw-bot: cr

>
> Quentin