linux-kernel - Re: [PATCH] mm/madvise: handle madvise_lock() failure during race unwinding

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Message-ID: <b3783c64-1f68-452d-ade2-1fc44cd8f080@lucifer.local>
Date: Mon, 2 Jun 2025 20:28:40 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Jann Horn <jannh@...gle.com>
Cc: SeongJae Park <sj@...nel.org>, Andrew Morton <akpm@...ux-foundation.org>,
        "Liam R. Howlett" <Liam.Howlett@...cle.com>,
        David Hildenbrand <david@...hat.com>,
        Shakeel Butt <shakeel.butt@...ux.dev>,
        Vlastimil Babka <vbabka@...e.cz>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, stable@...nel.org, Barry Song <21cnbao@...il.com>
Subject: Re: [PATCH] mm/madvise: handle madvise_lock() failure during race
 unwinding

On Mon, Jun 02, 2025 at 09:20:14PM +0200, Jann Horn wrote:
> @akpm FYI, this looks like it fixes a security bug in 6.15 (probably
> leads to UAF of VMA structs and page tables by racing madvise(...,
> MADV_GUARD_INSTALL) with concurrent faults)

Hmm MADV_GUARD_INSTALL / MADV_GUARD_REMOVE require only a read lock, so
madvise_lock() will be:


	if (madvise_need_mmap_write(behavior)) { <--- nope
		if (mmap_write_lock_killable(mm))
			return -EINTR;
	} else {
		mmap_read_lock(mm); <---- this branch
	}
	return 0;

So for guard install, which is the only thing that can return -ERESTARTNOINTR
madvise_lock() ignoring the return value is essentially a no-op no?

Am I missing something?

>
> On Mon, Jun 2, 2025 at 7:49 PM SeongJae Park <sj@...nel.org> wrote:
> > When unwinding race on -ERESTARTNOINTR handling of process_madvise(),
> > madvise_lock() failure is ignored.  Check the failure and abort
> > remaining works in the case.
> >
> > Fixes: 4000e3d0a367 ("mm/madvise: remove redundant mmap_lock operations from process_madvise()")
> > Cc: stable@...nel.org
> > Reported-by: Barry Song <21cnbao@...il.com>
> > Closes: https://lore.kernel.org/CAGsJ_4xJXXO0G+4BizhohSZ4yDteziPw43_uF8nPXPWxUVChzw@mail.gmail.com
> > Signed-off-by: SeongJae Park <sj@...nel.org>
>
> Reviewed-by: Jann Horn <jannh@...gle.com>