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Wed, 17 Mar 2021 07:13:45 +0000 Received: from [10.2.48.16] (172.20.145.6) by HQMAIL107.nvidia.com (172.20.187.13) with Microsoft SMTP Server (TLS) id 15.0.1497.2; Wed, 17 Mar 2021 07:13:44 +0000 Subject: Re: [PATCH] mm: cma: Fix potential null dereference on pointer cma To: Colin King , Andrew Morton , Minchan Kim , Stephen Rothwell , Greg Kroah-Hartman , CC: , References: <20210316100433.17665-1-colin.king@canonical.com> From: John Hubbard Message-ID: Date: Wed, 17 Mar 2021 00:13:31 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1 MIME-Version: 1.0 In-Reply-To: <20210316100433.17665-1-colin.king@canonical.com> Content-Type: text/plain; charset="utf-8"; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [172.20.145.6] X-ClientProxiedBy: HQMAIL111.nvidia.com (172.20.187.18) To HQMAIL107.nvidia.com (172.20.187.13) X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: 8ee14521-9ffb-409c-09e6-08d8e9143414 X-MS-TrafficTypeDiagnostic: DM6PR12MB4957: X-Microsoft-Antispam-PRVS: X-MS-Oob-TLC-OOBClassifiers: OLM:2803; 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X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 17 Mar 2021 07:13:45.1583 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 8ee14521-9ffb-409c-09e6-08d8e9143414 X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[216.228.112.34];Helo=[mail.nvidia.com] X-MS-Exchange-CrossTenant-AuthSource: CO1NAM11FT043.eop-nam11.prod.protection.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM6PR12MB4957 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 3/16/21 3:04 AM, Colin King wrote: > From: Colin Ian King > > At the start of the function there is a null pointer check on cma > and then branch to error handling label 'out'. The subsequent call > to cma_sysfs_fail_pages_count dereferences cma, hence there is a > potential null pointer deference issue. Fix this by only calling As far as I can tell, it's not possible to actually cause that null failure with the existing kernel code paths. *Might* be worth mentioning that here (unless I'm wrong), but either way, looks good, so: Reviewed-by: John Hubbard thanks, -- John Hubbard NVIDIA > cma_sysfs_fail_pages_count if cma is not null. > > Addresses-Coverity: ("Dereference after null check") > Fixes: dc4764f7e9ac ("mm: cma: support sysfs") > Signed-off-by: Colin Ian King > --- > mm/cma.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/mm/cma.c b/mm/cma.c > index 6d4dbafdb318..90e27458ddb7 100644 > --- a/mm/cma.c > +++ b/mm/cma.c > @@ -512,7 +512,8 @@ struct page *cma_alloc(struct cma *cma, size_t count, unsigned int align, > cma_sysfs_alloc_pages_count(cma, count); > } else { > count_vm_event(CMA_ALLOC_FAIL); > - cma_sysfs_fail_pages_count(cma, count); > + if (cma) > + cma_sysfs_fail_pages_count(cma, count); > } > > return page; >