linux-kernel - Re: [RFC PATCH] double free in decompressor.c

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Message-ID: <528FE805.1080001@lougher.demon.co.uk>
Date:	Fri, 22 Nov 2013 23:25:57 +0000
From:	Phillip Lougher <phillip@...gher.demon.co.uk>
To:	Geyslan Gregório Bem <geyslan@...il.com>
CC:	phillip@...ashfs.org.uk, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] double free in decompressor.c

On 22/11/13 21:50, Geyslan Gregório Bem wrote:
> Coverity caught double free possibility (CID 1130962).
>
> I can patch this, but I have to know if is correct to free comp_opts
> in the function squashfs_decompressor_create() or it had to be done in
> the caller. My bet is the caller.
>
>
> 128void *squashfs_decompressor_setup(struct super_block *sb, unsigned
> short flags)
> 129{
> 130        struct squashfs_sb_info *msblk = sb->s_fs_info;
> 131        void *stream, *comp_opts = get_comp_opts(sb, flags);
> 132
>
> 1. Condition "IS_ERR(comp_opts)", taking false branch
> 133        if (IS_ERR(comp_opts))
> 134                return comp_opts;
> 135
>
> 2. freed_arg: "squashfs_decompressor_create(struct squashfs_sb_info *,
> void *)" frees "comp_opts".[show details]
> 136        stream = squashfs_decompressor_create(msblk, comp_opts);
>
> 3. Condition "IS_ERR(stream)", taking true branch
> 137        if (IS_ERR(stream))

FALSE positive.

squashfs_decompressor_create() frees comp_opts only on success.

If IS_ERR(stream) is true, then comp_opts has not been freed by
squashfs_decompressor_create().

Phillip


>
> CID 1130962 (#1 of 1): Double free (USE_AFTER_FREE)4. double_free:
> Calling "kfree(void const *)" frees pointer "comp_opts" which has
> already been freed.
> 138                kfree(comp_opts);
> 139
> 140        return stream;
> 141}
>
>

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