Re: [PATCH] vhost-scsi: Prevent OOM from invalid protection SGL count

[Michael S. Tsirkin]

On Fri, Jul 17, 2026 at 10:13:36AM -0500, Mike Christie wrote:
> cc'ing Linfeng.
> 
> Linfeng also reported this bug and provided a patch that has your check and
> an extra check to avoid calling into the function in the first place. It's
> been stuck in some other list.
> 
> I think it might be best for Linfeng to re-submit their patch now so it can
> get merged. For that patch, I think there was one outstanding question left
> where Michael had asked if the issue was found with AI so the proper tag
> could be added. I don't think that question was responded to.

Right, was waiting for that.

> 
> On 7/17/26 9:22 AM, Jia Jia wrote:
> > The protection SGL path passes the result of vhost_scsi_calc_sgls()
> > directly to sg_alloc_table_chained(). The helper returns a negative
> > errno when the iterator is invalid or the request exceeds the segment
> > limit. The negative errno is then treated as a very large unsigned count
> > and sends the request into the SGL allocation path with an invalid size.
> > 
> > Repeated malformed T10-PI submissions from a host-side application caused
> > memory usage to rise sharply. MemAvailable fell to about 200 MB, and PSI
> > full avg10 reached about 1.46. The OOM killer terminated several userspace
> > processes before the endpoint cleanup completed. The kernel log included:
> > 
> >      [17036.451028] Out of memory: Killed process 2345 (systemd)
> >      [17036.493325] Out of memory: Killed process 2349 (sd-pam)
> >      [17078.265127] Out of memory: Killed process 1793 (networkd-dispat)
> > 
> > Return the calculation error before setting up the protection SGL. This
> > keeps the protection path consistent with the data SGL path and prevents
> > the invalid count from entering the allocation path.
> > 
> > Fixes: bca939d5bcd0 ("vhost-scsi: Dynamically allocate scatterlists")
> > Cc: stable@xxxxxxxxxxxxxxx
> > Signed-off-by: Jia Jia <physicalmtea@xxxxxxxxx>
> > ---
> >   drivers/vhost/scsi.c | 3 +++
> >   1 file changed, 3 insertions(+)
> > 
> > diff --git a/drivers/vhost/scsi.c b/drivers/vhost/scsi.c
> > index 9a1253b9d..8486652fd 100644
> > --- a/drivers/vhost/scsi.c
> > +++ b/drivers/vhost/scsi.c
> > @@ -972,6 +972,9 @@ vhost_scsi_mapal(struct vhost_scsi *vs, struct vhost_scsi_cmd *cmd,
> >   	if (prot_bytes) {
> >   		sgl_count = vhost_scsi_calc_sgls(prot_iter, prot_bytes,
> >   						 VHOST_SCSI_PREALLOC_PROT_SGLS);
> > +		if (sgl_count < 0)
> > +			return sgl_count;
> > +
> >   		cmd->prot_table.sgl = cmd->prot_sgl;
> >   		ret = sg_alloc_table_chained(&cmd->prot_table, sgl_count,
> >   					     cmd->prot_table.sgl,
> > -- 
> > 2.43.0
> >