linux-hardening - Re: [PATCH] udf: Use unsigned variables for size calculations

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Date:   Tue, 7 Feb 2023 13:07:45 +0100
From:   Jan Kara <jack@...e.cz>
To:     Kees Cook <keescook@...omium.org>
Cc:     Jan Kara <jack@...e.com>, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH] udf: Use unsigned variables for size calculations

On Sat 04-02-23 10:34:27, Kees Cook wrote:
> To avoid confusing the compiler about possible negative sizes, switch
> various size variables that can never be negative from int to u32. Seen
> with GCC 13:
> 
> ../fs/udf/directory.c: In function 'udf_copy_fi':
> ../include/linux/fortify-string.h:57:33: warning: '__builtin_memcpy' pointer overflow between offset 80 and size [-2147483648, -1] [-Warray-bounds=]
>    57 | #define __underlying_memcpy     __builtin_memcpy
>       |                                 ^
> ...
> ../fs/udf/directory.c:102:9: note: in expansion of macro 'memcpy'
>   102 |         memcpy(&iter->fi, iter->bh[0]->b_data + off, len);
>       |         ^~~~~~
> 
> Cc: Jan Kara <jack@...e.com>
> Signed-off-by: Kees Cook <keescook@...omium.org>

Sigh. OK, applied but I really wish gcc was more clever because the
arithmetics making sure we cannot see negative values there is literaly in
two lines above the memcpy...

								Honza

> ---
>  fs/udf/directory.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/udf/directory.c b/fs/udf/directory.c
> index 2e13c4b5fb81..e0bb73d414dd 100644
> --- a/fs/udf/directory.c
> +++ b/fs/udf/directory.c
> @@ -71,8 +71,9 @@ static int udf_verify_fi(struct udf_fileident_iter *iter)
>  static int udf_copy_fi(struct udf_fileident_iter *iter)
>  {
>  	struct udf_inode_info *iinfo = UDF_I(iter->dir);
> -	int blksize = 1 << iter->dir->i_blkbits;
> -	int err, off, len, nameoff;
> +	u32 blksize = 1 << iter->dir->i_blkbits;
> +	u32 off, len, nameoff;
> +	int err;
>  
>  	/* Skip copying when we are at EOF */
>  	if (iter->pos >= iter->dir->i_size) {
> -- 
> 2.34.1
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR