Re: [PATCH bpf-next v2 2/2] bpftool: Fix UAF in get_delegate_value

[Tao Chen]

在 2025/9/18 00:30, Quentin Monnet 写道:
> 2025-09-17 11:47 UTC+0800 ~ Tao Chen <chen.dylane@xxxxxxxxx>
> > 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@xxxxxxxxx>
> > ---
> >   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?
>
> Quentin

Well, actually, there is no special purpose about using macros, i will
use functions as you and Andrri suggested, thanks.

--
Best Regards
Tao Chen