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

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Message-ID: <523d8d6c-de99-435f-a01b-1bac72810d53@kernel.org>
Date: Wed, 17 Sep 2025 17:30:48 +0100
From: Quentin Monnet <qmo@...nel.org>
To: 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
Cc: bpf@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next v2 2/2] bpftool: Fix UAF in get_delegate_value

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?

Quentin