linux-kernel - Re: [PATCH] ext4: mballoc: avoid garbage value from err

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Message-ID: <CAKwvOdk-fdJr9TcgUnOhCiU0LvD2Qe_c+6YOe-c1k0Ukm+negA@mail.gmail.com>
Date:   Mon, 24 Jul 2023 10:19:02 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Su Hui <suhui@...china.com>
Cc:     tytso@....edu, adilger.kernel@...ger.ca, nathan@...nel.org,
        trix@...hat.com, linux-ext4@...r.kernel.org,
        linux-kernel@...r.kernel.org, llvm@...ts.linux.dev,
        kernel-janitors@...r.kernel.org
Subject: Re: [PATCH] ext4: mballoc: avoid garbage value from err

On Sun, Jul 23, 2023 at 10:46 PM Su Hui <suhui@...china.com> wrote:
>
> clang warning: fs/ext4/mballoc.c, line 4178, column 6
> Branch condition evaluates to a garbage value.

Specifically this is clang's static analysis; not the compiler itself.

>
> err is uninitialized and will be judged when it enters the
> loop first time and the condition "!ext4_sb_block_valid()"
> is true. Although this can't make problems now, it's better
> to correct it.
>
> Signed-off-by: Su Hui <suhui@...china.com>

Hi Su,
Thanks for the patch!  I see what the warning is getting at;

If `len <= 0` then `err` is never initialized, then is used at line
4178 (that is UB).

Would you mind sending a v2 with the commit message updated to reflect
the above points?  I'd be happy to sign-off on that.

> ---
>  fs/ext4/mballoc.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> index 21b903fe546e..769000c970b0 100644
> --- a/fs/ext4/mballoc.c
> +++ b/fs/ext4/mballoc.c
> @@ -4084,7 +4084,7 @@ void ext4_mb_mark_bb(struct super_block *sb, ext4_fsblk_t block,
>         struct ext4_sb_info *sbi = EXT4_SB(sb);
>         ext4_group_t group;
>         ext4_grpblk_t blkoff;
> -       int i, err;
> +       int i, err = 0;
>         int already;
>         unsigned int clen, clen_changed, thisgrp_len;
>
> --
> 2.30.2
>
>


-- 
Thanks,
~Nick Desaulniers