linux-kernel - Re: [PATCH][next] mm/vmalloc: Fix read of pointer area after it has been free'd

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Date:   Tue, 30 Mar 2021 12:52:54 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Colin King <colin.king@...onical.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Nicholas Piggin <npiggin@...il.com>, linux-mm@...ck.org,
        kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH][next] mm/vmalloc: Fix read of pointer area after it has
 been free'd

On Mon, Mar 29, 2021 at 06:14:34PM +0100, Matthew Wilcox wrote:
> On Mon, Mar 29, 2021 at 06:07:30PM +0100, Colin King wrote:
> > From: Colin Ian King <colin.king@...onical.com>
> > 
> > Currently the memory pointed to by area is being freed by the
> > free_vm_area call and then area->nr_pages is referencing the
> > free'd object. Fix this swapping the order of the warn_alloc
> > message and the free.
> > 
> > Addresses-Coverity: ("Read from pointer after free")
> > Fixes: 014ccf9b888d ("mm/vmalloc: improve allocation failure error messages")
> 
> i don't have this git sha.  if this is -next, the sha ids aren't stable
> and shouldn't be referenced in commit logs, because these fixes should
> just be squashed into the not-yet-upstream commits.

The fixes tag won't "be referenced in the commit logs" because Andew
is going to fold it in.  And the "mm/vmalloc: improve allocation failure
error messages" information is useful.

More generally there are a bunch trees which rebase often but it's
humanly impossible to remember which ones they are and there is no
automated way to track it either.  If the maintainer is going to rebase
then they're going to have to think about Fixes tags a bit.  Normally
rebased trees fold fixes so it's not an issue.  Otherwise it would be
easy to write a script to correct the Fixes tags during a rebase.

In other words, my view is that everyone should just use the same Fixes
tag format everywhere.

regards,
dan carpenter