linux-kernel - Re: [PATCH] objtool: check: Fix NULL pointer dereference

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Date:   Tue, 31 Mar 2020 17:04:05 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     "Gustavo A. R. Silva" <gustavo@...eddedor.com>
Cc:     Peter Zijlstra <peterz@...radead.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] objtool: check: Fix NULL pointer dereference

On Mon, Mar 30, 2020 at 07:20:40PM -0500, Gustavo A. R. Silva wrote:
> In case func is null, there is a null pointer dereference at 2029:
> 
> 2029                 WARN("%s uses BP as a scratch register",
> 2030                      func->name);
> 
> Fix this by null-checking func.
> 
> Addresses-Coverity-ID: 1492002 ("Dereference after null check")
> Fixes: c705cecc8431 ("objtool: Track original function across branches")
> Signed-off-by: Gustavo A. R. Silva <gustavo@...eddedor.com>
> ---
>  tools/objtool/check.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/tools/objtool/check.c b/tools/objtool/check.c
> index e3bb76358148..182cc48fa892 100644
> --- a/tools/objtool/check.c
> +++ b/tools/objtool/check.c
> @@ -2025,7 +2025,7 @@ static int validate_return(struct symbol *func, struct instruction *insn, struct
>  		return 1;
>  	}
>  
> -	if (state->bp_scratch) {
> +	if (func && state->bp_scratch) {
>  		WARN("%s uses BP as a scratch register",
>  		     func->name);
>  		return 1;

We should still do the warning even if there's no func.  I'll make a
slightly different patch which unconditionally uses WARN_FUNC().

I'll give you Reported-by credit and keep the coverity tag.  Thanks!

-- 
Josh