linux-kernel - Re: [PATCH v3] vmcore: prevent PT_NOTE p

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Message-ID: <20140205134355.GD6042@redhat.com>
Date:	Wed, 5 Feb 2014 08:43:55 -0500
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Greg Pearson <greg.pearson@...com>
Cc:	akpm@...ux-foundation.org, d.hatayama@...fujitsu.com,
	holzheu@...ux.vnet.ibm.com, dhowells@...hat.com,
	paul.gortmaker@...driver.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] vmcore: prevent PT_NOTE p_memsz overflow during
 header update

On Wed, Feb 05, 2014 at 08:39:12AM -0500, Vivek Goyal wrote:
> On Tue, Feb 04, 2014 at 04:25:52PM -0700, Greg Pearson wrote:
> 
> [..]
> > diff --git a/fs/proc/vmcore.c b/fs/proc/vmcore.c
> > index 2ca7ba0..88d4585 100644
> > --- a/fs/proc/vmcore.c
> > +++ b/fs/proc/vmcore.c
> > @@ -468,17 +468,24 @@ static int __init update_note_header_size_elf64(const Elf64_Ehdr *ehdr_ptr)
> >  			return rc;
> >  		}
> >  		nhdr_ptr = notes_section;
> > -		while (real_sz < max_sz) {
> > -			if (nhdr_ptr->n_namesz == 0)
> > -				break;
> > +		while (nhdr_ptr->n_namesz != 0) {
> >  			sz = sizeof(Elf64_Nhdr) +
> >  				((nhdr_ptr->n_namesz + 3) & ~3) +
> >  				((nhdr_ptr->n_descsz + 3) & ~3);
> > +			if ((real_sz + sz) > max_sz) {
> > +				pr_warn("Warning: Exceeded p_memsz, dropping PT_NOTE entry n_namesz=0x%x, n_descsz=0x%x\n",
> > +					nhdr_ptr->n_namesz, nhdr_ptr->n_descsz);
> 
> You will need line break in pr_warn(). Too long a line. Limit it 80
> columns per line.
> 
> > +				break;
> > +			}
> >  			real_sz += sz;
> >  			nhdr_ptr = (Elf64_Nhdr*)((char*)nhdr_ptr + sz);
> >  		}
> >  		kfree(notes_section);
> >  		phdr_ptr->p_memsz = real_sz;
> > +		if (real_sz == 0) {
> > +			pr_warn("Warning: Zero PT_NOTE entries found\n");
> > +			return -EINVAL;
> 
> Given the fact that this is the first time I have heard about a PT_NOTE
> being corrup, I will be fine with this patch too. If one encounters
> an empty PT_NOTE, error out and don't create vmcore.
> 
> So please repost this patch with line lenght fixed.

Hi Greg,

Is there any more debugging info on why a PT_NOTE is getting corrupt. Did
you get a chance to debug it further. This patch is more of a band-aid and
real problem is why note is getting corrupted and we need to chase that
down and fix that.

Thanks
Vivek
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