linux-kernel - [PATCH] ata: pata_platform: Fix a NULL pointer dereference in __pata_platform

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Date:   Tue, 25 Jan 2022 00:45:25 +0800
From:   Zhou Qingyang <zhou1615@....edu>
To:     zhou1615@....edu
Cc:     kjlu@....edu, Damien Le Moal <damien.lemoal@...nsource.wdc.com>,
        Alexander Shiyan <shc_work@...l.ru>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Jens Axboe <axboe@...nel.dk>, linux-ide@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] ata: pata_platform: Fix a NULL pointer dereference in __pata_platform_probe()

In __pata_platform_probe(), devm_kzalloc() is assigned to ap->ops and
there is a dereference of it right after that, which could introduce a
NULL pointer dereference bug.

Fix this by adding a NULL check of ap->ops.

This bug was found by a static analyzer.

Builds with 'make allyesconfig' show no new warnings,
and our static analyzer no longer warns about this code.

Fixes: f3d5e4f18dba ("ata: pata_of_platform: Allow to use 16-bit wide data transfer")
Signed-off-by: Zhou Qingyang <zhou1615@....edu>
---
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.

 drivers/ata/pata_platform.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/ata/pata_platform.c b/drivers/ata/pata_platform.c
index 028329428b75..021ef9cbcbc1 100644
--- a/drivers/ata/pata_platform.c
+++ b/drivers/ata/pata_platform.c
@@ -128,6 +128,8 @@ int __pata_platform_probe(struct device *dev, struct resource *io_res,
 	ap = host->ports[0];
 
 	ap->ops = devm_kzalloc(dev, sizeof(*ap->ops), GFP_KERNEL);
+	if (ap->ops)
+		return -ENOMEM;
 	ap->ops->inherits = &ata_sff_port_ops;
 	ap->ops->cable_detect = ata_cable_unknown;
 	ap->ops->set_mode = pata_platform_set_mode;
-- 
2.25.1