linux-kernel - Re: [PATCH v2] EDAC/ghes: Fix buffer overflow in ghes_edac

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Date:   Mon, 25 Jul 2022 12:45:18 +0200
From:   Robert Richter <rric@...nel.org>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Toshi Kani <toshi.kani@....com>, mchehab@...nel.org,
        elliott@....com, linux-edac@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] EDAC/ghes: Fix buffer overflow in ghes_edac_register()

On 25.07.22 12:14:21, Borislav Petkov wrote:
> On Mon, Jul 25, 2022 at 11:53:06AM +0200, Robert Richter wrote:
> > The dimm->label buffer must be pre-initialized zero. This broke with:
> > 
> >  b9cae27728d1 EDAC/ghes: Scan the system once on driver init
> > 
> > since krealloc/krealloc_array() does not zero out the new allocated
> > buffer for struct dimm_info in enumerate_dimms(). This uninitialized
> > broken struct is then copied in ghes_edac_register() to the final
> > dimm_info destination. Originally, before b9cae27728d1, the struct was
> > zero initialized with kzalloc'ed by edac_mc_alloc() and directly used.
> > Now, that a copy is created first, this copy must be also zero
> > initialized.
> > 
> > IMO this is the proper fix:
> 
> Maybe, but this needs fixing too:
> 
> 	/* both strings must be non-zero */
> 	if (bank && *bank && device && *device)
> 
> Obviously one of those strings are zero coming from that BIOS...

But the label is pre-initialized in edac_mc_alloc_dimms():

	p = dimm->label;
	n = snprintf(p, len, "mc#%u", mci->mc_idx);

You check if the label is emtpy when copying it in
ghes_edac_register():

	if (strlen(src->label))
		memcpy(dst->label, src->label, sizeof(src->label));

So if there is nothing that comes from the bios, this default label
string from edac_mc_alloc_dimms() will be used.

If you write "N/A" to the label instead, the sysfs dimm_label values
wont be unique any longer between dimms, which might break existing
applications.

-Robert

> 
> -- 
> Regards/Gruss,
>     Boris.
> 
> https://people.kernel.org/tglx/notes-about-netiquette