Subject: Re: [PATCH bpf-next] selftests/bpf: Bump and validate MAX_SYMS

From: Stanislav Fomichev <[email-masked]>
Date: Thu, 6 Jul 2023 10:46:27 -0700

On 07/06, Björn Töpel wrote:
> From: Björn Töpel <[email-masked]>
> 
> BPF tests that load /proc/kallsyms, e.g. bpf_cookie, will perform a
> buffer overrun if the number of syms on the system is larger than
> MAX_SYMS.
> 
> Bump the MAX_SYMS to 400000, and add a runtime check that bails out if
> the maximum is reached.
> 
> Signed-off-by: Björn Töpel <[email-masked]>

Acked-by: Stanislav Fomichev <[email-masked]>

OTOH, should be easy to convert this to malloc/realloc? That should fix
it once and for all and avoid future need to bump the limit?

> ---
>  tools/testing/selftests/bpf/trace_helpers.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/testing/selftests/bpf/trace_helpers.c b/tools/testing/selftests/bpf/trace_helpers.c
> index 9b070cdf44ac..f83d9f65c65b 100644
> --- a/tools/testing/selftests/bpf/trace_helpers.c
> +++ b/tools/testing/selftests/bpf/trace_helpers.c
> @@ -18,7 +18,7 @@
>  #define TRACEFS_PIPE	"/sys/kernel/tracing/trace_pipe"
>  #define DEBUGFS_PIPE	"/sys/kernel/debug/tracing/trace_pipe"
>  
> -#define MAX_SYMS 300000
> +#define MAX_SYMS 400000
>  static struct ksym syms[MAX_SYMS];
>  static int sym_cnt;
>  
> @@ -46,6 +46,9 @@ int load_kallsyms_refresh(void)
>  			break;
>  		if (!addr)
>  			continue;
> +		if (i >= MAX_SYMS)
> +			return -EFBIG;
> +
>  		syms[i].addr = (long) addr;
>  		syms[i].name = strdup(func);
>  		i++;
> 
> base-commit: fd283ab196a867f8f65f36913e0fadd031fcb823
> -- 
> 2.39.2
>