linux-kernel - Re: [PATCH] elf: fix NT

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Message-Id: <20180112145208.b054caf00c6fa666cc1a1c9c@linux-foundation.org>
Date:   Fri, 12 Jan 2018 14:52:08 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Alexey Dobriyan <adobriyan@...il.com>
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH] elf: fix NT_FILE integer overflow

On Fri, 12 Jan 2018 23:34:27 +0300 Alexey Dobriyan <adobriyan@...il.com> wrote:

> If vm.max_map_count bumped above 2^26 (67+ mil) and system has enough
> RAM to allocate all the VMAs (~12.8 GB on Fedora 27 with 200-byte VMAs),
> then it should be possible to overflow 32-bit "size", pass paranoia check,
> allocate very little vmalloc space and oops while writing into vmalloc
> guard page...
> 
> But I didn't test this, only coredump of regular process.
> 
> ...
>
> --- a/fs/binfmt_elf.c
> +++ b/fs/binfmt_elf.c
> @@ -1599,6 +1599,8 @@ static int fill_files_note(struct memelfnote *note)
>  
>  	/* *Estimated* file count and total data size needed */
>  	count = current->mm->map_count;
> +	if (count > UINT_MAX / 64)
> +		return -EINVAL;
>  	size = count * 64;
>  
>  	names_ofs = (2 + 3 * count) * sizeof(data[0]);

Why not make `size' a ulong (or size_t)?  That seems to be the
appropriate type and the code will then immediately barf over the
MAX_FILE_NOTE_SIZE comparison anyway.