linux-kernel - Re: [PATCH][sas] Fix potential NULL pointer dereference bug in sas_smp_get_phy

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Message-Id: <200707280113.33766.jesper.juhl@gmail.com>
Date:	Sat, 28 Jul 2007 01:13:33 +0200
From:	Jesper Juhl <jesper.juhl@...il.com>
To:	James Bottomley <James.Bottomley@...eleye.com>
Cc:	linux-scsi@...r.kernel.org,
	Luben Tuikov <luben_tuikov@...ptec.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Jesper Juhl <jesper.juhl@...il.com>
Subject: Re: [PATCH][sas] Fix potential NULL pointer dereference bug in sas_smp_get_phy_events()



On 28/07/07, James Bottomley <James.Bottomley@...eleye.com> wrote:
> On Fri, 2007-07-27 at 23:27 +0200, Jesper Juhl wrote:
> > In sas_smp_get_phy_events() we never test if the call to
> > alloc_smp_req(RPEL_REQ_SIZE) succeeds or fails. That means we run
> > the risk of dereferencing a NULL pointer if it does fail. Far
> > better to test if we got NULL back and in that case return -ENOMEM
> > just as we already do for the other memory allocation in that
> > function.
> > This patch reworks the memory allocation a bit to deal with it
> > (compile tested only).
> >
> >
> > Signed-off-by: Jesper Juhl <jesper.juhl@...il.com>
> > ---
> >
> >  drivers/scsi/libsas/sas_expander.c |   11 +++++++++--
> >  1 files changed, 9 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/scsi/libsas/sas_expander.c b/drivers/scsi/libsas/sas_expander.c
> > index b500f0c..85f5145 100644
> > --- a/drivers/scsi/libsas/sas_expander.c
> > +++ b/drivers/scsi/libsas/sas_expander.c
> > @@ -507,14 +507,21 @@ static int sas_dev_present_in_domain(struct asd_sas_port *port,
> >  int sas_smp_get_phy_events(struct sas_phy *phy)
> >  {
> >       int res;
> > +     u8 *req;
> > +     u8 *resp;
> >       struct sas_rphy *rphy = dev_to_rphy(phy->dev.parent);
> >       struct domain_device *dev = sas_find_dev_by_rphy(rphy);
> > -     u8 *req = alloc_smp_req(RPEL_REQ_SIZE);
> > -     u8 *resp = kzalloc(RPEL_RESP_SIZE, GFP_KERNEL);
> >
> > +     resp = kzalloc(RPEL_RESP_SIZE, GFP_KERNEL);
> 
> Actually, this should be alloc_smp_resp(RPEL_RESP_SIZE);
> 
> >       if (!resp)
> >               return -ENOMEM;
> >
> > +     req = alloc_smp_req(RPEL_REQ_SIZE);
> > +     if (!req) {
> > +             res = -ENOMEM;
> > +             goto out;
> > +     }
> 
> Just for the sake of being the same as all the rest of the code, the
> sequence should be
> 
>         req = alloc_smp_req(xxx_REQ_SIZE);
>         if (!req)
>                 return -ENOMEM;
> 
>         resp = alloc_smp_resp(xxx_RESP_SIZE);
>         if (!resp) {
>                 kfree(req);
>                 return -ENOMEM;
>         }
> 
> (allocate request then response).
> 
Fair enough. It makes the code a bit larger though : 

 My way, as per the original patch:
    text    data     bss     dec     hex filename
   13820       0       8   13828    3604 drivers/scsi/libsas/sas_expander.o
 Your way, as per this patch:
    text    data     bss     dec     hex filename
   13832       0       8   13840    3610 drivers/scsi/libsas/sas_expander.o

I hope this patch is acceptable : 


In sas_smp_get_phy_events() we never test if the call to
alloc_smp_req(RPEL_REQ_SIZE) succeeds or fails. That means we run
the risk of dereferencing a NULL pointer if it does fail. Far
better to test if we got NULL back and in that case return -ENOMEM
just as we already do for the other memory allocation in that
function.
This patch should take care of it (compile tested only).


Signed-off-by: Jesper Juhl <jesper.juhl@...il.com>
---

 drivers/scsi/libsas/sas_expander.c |   13 ++++++++++---
 1 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/drivers/scsi/libsas/sas_expander.c b/drivers/scsi/libsas/sas_expander.c
index b500f0c..e98d2b9 100644
--- a/drivers/scsi/libsas/sas_expander.c
+++ b/drivers/scsi/libsas/sas_expander.c
@@ -507,14 +507,21 @@ static int sas_dev_present_in_domain(struct asd_sas_port *port,
 int sas_smp_get_phy_events(struct sas_phy *phy)
 {
 	int res;
+	u8 *req;
+	u8 *resp;
 	struct sas_rphy *rphy = dev_to_rphy(phy->dev.parent);
 	struct domain_device *dev = sas_find_dev_by_rphy(rphy);
-	u8 *req = alloc_smp_req(RPEL_REQ_SIZE);
-	u8 *resp = kzalloc(RPEL_RESP_SIZE, GFP_KERNEL);
 
-	if (!resp)
+	req = alloc_smp_req(RPEL_REQ_SIZE);
+	if (!req)
 		return -ENOMEM;
 
+	resp = alloc_smp_resp(RPEL_RESP_SIZE);
+	if (!resp) {
+		kfree(req);
+		return -ENOMEM;
+	}
+
 	req[1] = SMP_REPORT_PHY_ERR_LOG;
 	req[9] = phy->number;
 




> It looks like disc_resp could use a little love too (it's using the req
> alloc routines).
> 
I'll take a look at that later.


-- 
Jesper Juhl <jesper.juhl@...il.com>
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