linux-kernel - Re: [PATCH 3/5] fs/fs_parse: Fix 3 issues for validate_constant

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Message-ID: <20250411-beteuern-fusionieren-2a3d24f055d0@brauner>
Date: Fri, 11 Apr 2025 16:37:47 +0200
From: Christian Brauner <brauner@...nel.org>
To: Zijun Hu <zijun_hu@...oud.com>
Cc: Alexander Viro <viro@...iv.linux.org.uk>, Jan Kara <jack@...e.cz>, 
	David Howells <dhowells@...hat.com>, linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Zijun Hu <quic_zijuhu@...cinc.com>
Subject: Re: [PATCH 3/5] fs/fs_parse: Fix 3 issues for
 validate_constant_table()

On Thu, Apr 10, 2025 at 07:45:29PM +0800, Zijun Hu wrote:
> From: Zijun Hu <quic_zijuhu@...cinc.com>
> 
> Constant table array array[] which must end with a empty entry and fix
> below issues for validate_constant_table(array, ARRAY_SIZE(array), ...):
> 
> - Always return wrong value for good constant table array which ends
>   with a empty entry.
> 
> - Imprecise error message for missorted case.
> 
> - Potential NULL pointer dereference.

I really dislike "potential NULL deref" without an explanation. Please
explain how this supposed NULL deref can happen.

> Fixes: 31d921c7fb96 ("vfs: Add configuration parser helpers")
> Signed-off-by: Zijun Hu <quic_zijuhu@...cinc.com>
> ---
>  fs/fs_parser.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/fs_parser.c b/fs/fs_parser.c
> index e635a81e17d965df78ffef27f6885cd70996c6dd..ef7876340a917876bc40df9cdde9232204125a75 100644
> --- a/fs/fs_parser.c
> +++ b/fs/fs_parser.c
> @@ -399,6 +399,9 @@ bool validate_constant_table(const struct constant_table *tbl, size_t tbl_size,
>  	}
>  
>  	for (i = 0; i < tbl_size; i++) {
> +		if (!tbl[i].name && (i + 1 == tbl_size))
> +			break;
> +
>  		if (!tbl[i].name) {
>  			pr_err("VALIDATE C-TBL[%zu]: Null\n", i);
>  			good = false;
> @@ -411,13 +414,13 @@ bool validate_constant_table(const struct constant_table *tbl, size_t tbl_size,
>  				good = false;
>  			}
>  			if (c > 0) {
> -				pr_err("VALIDATE C-TBL[%zu]: Missorted %s>=%s\n",
> +				pr_err("VALIDATE C-TBL[%zu]: Missorted %s>%s\n",
>  				       i, tbl[i-1].name, tbl[i].name);
>  				good = false;
>  			}
>  		}
>  
> -		if (tbl[i].value != special &&
> +		if (tbl[i].name && tbl[i].value != special &&
>  		    (tbl[i].value < low || tbl[i].value > high)) {
>  			pr_err("VALIDATE C-TBL[%zu]: %s->%d const out of range (%d-%d)\n",
>  			       i, tbl[i].name, tbl[i].value, low, high);
> 
> -- 
> 2.34.1
>