From: John Garry <john.garry@huawei.com>
To: Zhou Qingyang <zhou1615@umn.edu>
Cc: <kjlu@umn.edu>, "James E.J. Bottomley" <jejb@linux.ibm.com>,
"Martin K. Petersen" <martin.petersen@oracle.com>,
Jason Yan <yanaijie@huawei.com>,
Himanshu Madhani <himanshu.madhani@oracle.com>,
Jack Wang <jinpu.wang@ionos.com>,
Luo Jiaxing <luojiaxing@huawei.com>,
Bart Van Assche <bvanassche@acm.org>,
James Bottomley <James.Bottomley@SteelEye.com>,
<linux-scsi@vger.kernel.org>, <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] scsi: libsas: Fix a NULL pointer dereference in sas_ex_discover_expander()
Date: Mon, 6 Dec 2021 15:09:47 +0000 [thread overview]
Message-ID: <b757aabe-5231-64bc-8ad5-cedac79b0f43@huawei.com> (raw)
In-Reply-To: <20211130171629.201026-1-zhou1615@umn.edu>
On 30/11/2021 17:16, Zhou Qingyang wrote:
I'd have "scsi: libsas: Improve error handling in
sas_ex_discover_expander()"
> In sas_ex_discover_expander(), sas_port_alloc() is assigned to phy->port
"sas_port_alloc() is assigned to phy->port" - the function is not assigned
> and used in sas_port_add(). sas_port_add() further passes phy->port to
> list_empty(), and there is a dereference of it in list_empty(), which
> could lead to a NULL pointer dereference on failure of
> sas_port_alloc().
>
> This patch imitates the same error-handling logic in
> sas_ex_discover_end_dev().
git grep 'This patch' Documentation/process/submitting-patches.rst
>
> Fix this bug by adding checks for phy->port and sas_port_add().
>
> This bug was found by a static analyzer. The analysis employs
> differential checking to identify inconsistent security operations
> (e.g., checks or kfrees) between two code paths and confirms that the
> inconsistent operations are not recovered in the current function or
> the callers, so they constitute bugs.
>
> Note that, as a bug found by static analysis, it can be a false
> positive or hard to trigger. Multiple researchers have cross-reviewed
> the bug.
Who are these researchers?
>
> Builds with CONFIG_SCSI_SAS_LIBSAS=m show no new warnings,
> and our static analyzer no longer warns about this code.
This is all implied by sending the patch in the first place
>
> Fixes: 2908d778ab3e ("[SCSI] aic94xx: new driver")
personally I don't think that this is a fix - the code is old and
already had BUG_ON()
> Signed-off-by: Zhou Qingyang <zhou1615@umn.edu>
> ---
> drivers/scsi/libsas/sas_expander.c | 11 +++++++++--
> 1 file changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/scsi/libsas/sas_expander.c b/drivers/scsi/libsas/sas_expander.c
> index c2150a818423..7530b1773d6b 100644
> --- a/drivers/scsi/libsas/sas_expander.c
> +++ b/drivers/scsi/libsas/sas_expander.c
> @@ -957,9 +957,16 @@ static struct domain_device *sas_ex_discover_expander(
> return NULL;
>
> phy->port = sas_port_alloc(&parent->rphy->dev, phy_id);
> - /* FIXME: better error handling */
> - BUG_ON(sas_port_add(phy->port) != 0);
> + if (unlikely(!phy->port)) {
no need for unlikely() - this is not fastpath
> + sas_put_device(child);
> + return NULL;
> + }
>
> + if (sas_port_add(phy->port) != 0) {
> + sas_port_free(phy->port);
> + sas_put_device(child);
better have a goto error now as we're replicting code, including what is
already there for the sas_discover_expander() failure error path
> + return NULL;
> + }
>
> switch (phy->attached_dev_type) {
> case SAS_EDGE_EXPANDER_DEVICE:
>
prev parent reply other threads:[~2021-12-06 15:14 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-30 17:16 [PATCH] scsi: libsas: Fix a NULL pointer dereference in sas_ex_discover_expander() Zhou Qingyang
2021-12-06 15:09 ` John Garry [this message]
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