linux-kernel - Re: [syzbot] [mm?] general protection fault in dequeue_hugetlb_folio

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Message-ID: <ZmkuH8R2XJZEvJwh@localhost.localdomain>
Date: Wed, 12 Jun 2024 07:11:59 +0200
From: Oscar Salvador <osalvador@...e.de>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: syzbot <syzbot+569ed13f4054f271087b@...kaller.appspotmail.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	muchun.song@...ux.dev, syzkaller-bugs@...glegroups.com,
	Vivek Kasireddy <vivek.kasireddy@...el.com>
Subject: Re: [syzbot] [mm?] general protection fault in
 dequeue_hugetlb_folio_nodemask (2)

On Tue, Jun 11, 2024 at 07:52:06PM +0200, Oscar Salvador wrote:
> On Tue, Jun 11, 2024 at 07:46:33PM +0200, Oscar Salvador wrote:
> > On Tue, Jun 11, 2024 at 10:30:05AM -0700, Andrew Morton wrote:
> > > On Tue, 11 Jun 2024 03:34:25 -0700 syzbot <syzbot+569ed13f4054f271087b@...kaller.appspotmail.com> wrote:
> > > 
> > > > Hello,
> > > > 
> > > > syzbot found the following issue on:
> > > 
> > > Thanks.
> > > 
> > > > Call Trace:
> > > >  <TASK>
> > > >  alloc_hugetlb_folio_nodemask+0xae/0x3f0 mm/hugetlb.c:2603
> > > >  memfd_alloc_folio+0x15e/0x390 mm/memfd.c:75
> > > >  memfd_pin_folios+0x1066/0x1720 mm/gup.c:3864
> > > >  udmabuf_create+0x658/0x11c0 drivers/dma-buf/udmabuf.c:353
> > > >  udmabuf_ioctl_create drivers/dma-buf/udmabuf.c:420 [inline]
> > > >  udmabuf_ioctl+0x304/0x4f0 drivers/dma-buf/udmabuf.c:451
> > > >  vfs_ioctl fs/ioctl.c:51 [inline]
> > > >  __do_sys_ioctl fs/ioctl.c:907 [inline]
> > > >  __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:893
> > > >  do_syscall_x64 arch/x86/entry/common.c:52 [inline]
> > > >  do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
> > > >  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> > > 
> > > I think we can pretty confidently point at the series "mm/gup:
> > > Introduce memfd_pin_folios() for pinning memfd folios".  I'll drop the
> > > v14 series.  
> > 
> > jfyi: I am trying to reproduce this locally.
> 
> Actually, should not memfd_alloc_folio() pass htlb_alloc_mask() instead
> of GFP_USER to alloc_hugetlb_folio_nodemask? Or at least do
> GFP_HIGHUSER.

Ok, I spot the issue.
memfd_alloc_folio() was calling alloc_hugetlb_folio_nodemask with
preferred_nid being NUMA_NO_NODE, but that is bad as
dequeue_hugetlb_folio_nodemask will do:

zonelist = node_zonelist(nid, gfp_mask)

which will try to get node_zonelists from nid, but since nid is -1, heh.

The below patch fixes the issue for me, but I think that the right place
to fix this up would be alloc_hugetlb_folio_nodemask(), so we can place
the numa_node_id() if preferred_nid = NUMA_NO_NODE in there as a safety
net.
This way we catch this before exploding in case the user was not careful
enough.

I will cook up a patch shortly.

Another thing is why memfd_alloc_folio uses GFP_USER instead of
GFP_HIGHUSER, but that maybe because I see that memfd_pin_folios() is
used by some DMA driver which might not have access to HIGH_MEMORY.

diff --git a/mm/memfd.c b/mm/memfd.c
index 8035c6325e3c..2692f0298adc 100644
--- a/mm/memfd.c
+++ b/mm/memfd.c
@@ -68,12 +68,13 @@ static void memfd_tag_pins(struct xa_state *xas)
 struct folio *memfd_alloc_folio(struct file *memfd, pgoff_t idx)
 {
 #ifdef CONFIG_HUGETLB_PAGE
+	int nid = numa_node_id();
 	struct folio *folio;
 	int err;
 
 	if (is_file_hugepages(memfd)) {
 		folio = alloc_hugetlb_folio_nodemask(hstate_file(memfd),
-						     NUMA_NO_NODE,
+						     nid,
 						     NULL,
 						     GFP_USER,
 						     false);

> 
> 
> -- 
> Oscar Salvador
> SUSE Labs
> 

-- 
Oscar Salvador
SUSE Labs