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[147.46.126.79]) by smtp.gmail.com with ESMTPSA id 2-20020a170902c20200b00190f5e3bcd9sm15861251pll.23.2022.12.30.20.58.55 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 30 Dec 2022 20:58:56 -0800 (PST) From: Yoochan Lee To: davem@davemloft.net Cc: sparclinux@vger.kernel.org, linux-kernel@vger.kernel.org, Yoochan Lee Subject: [PATCH] \sbus: char: uctrl: Fix use-after-free in uctrl_open Date: Sat, 31 Dec 2022 13:58:44 +0900 Message-Id: <20221231045844.2038042-1-yoochan1026@gmail.com> X-Mailer: git-send-email 2.39.0 MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org A race condition may occur if the user physically removes the uctrl device while calling open(). This is a race condition between uctrl_open() function and the uctrl_remove() function, which may lead to Use-After-Free. Therefore, add a kref when open() uctrl driver and decrement the kref when close() and uctrl_remove() so that the race condition is not occured. ---------------CPU 0--------------------CPU 1----------------- | p =3D dev_get_drvdata(&op->dev); | ... | kfree(p); -- (1) uctrl_get_event_status(global _driver); =E2=80=94 (2) Signed-off-by: Yoochan Lee --- drivers/sbus/char/uctrl.c | 23 +++++++++++++++++++---- 1 file changed, 19 insertions(+), 4 deletions(-) diff --git a/drivers/sbus/char/uctrl.c b/drivers/sbus/char/uctrl.c index 05de0ce79cb9..17a8acdfc03a 100644 --- a/drivers/sbus/char/uctrl.c +++ b/drivers/sbus/char/uctrl.c @@ -189,6 +189,7 @@ static struct uctrl_driver { int irq; int pending; struct uctrl_status status; + struct kref *refcnt; } *global_driver; =20 static void uctrl_get_event_status(struct uctrl_driver *); @@ -204,12 +205,28 @@ uctrl_ioctl(struct file *file, unsigned int cmd, unsi= gned long arg) return 0; } =20 +static void uctrl_delete(struct kref *kref) +{ + struct uctrl_driver *p =3D container_of(kref, struct uctrl_driver, refcnt= ); + + misc_deregister(&uctrl_dev); + free_irq(p->irq, p); + of_iounmap(&op->resource[0], p->regs, resource_size(&op->resource[0])); + kfree(p); +} + +static int uctrl_close(struct inode *inode, struct file *file) +{ + kref_put(&global_driver->refcnt, uctrl_delete); +} + static int uctrl_open(struct inode *inode, struct file *file) { mutex_lock(&uctrl_mutex); uctrl_get_event_status(global_driver); uctrl_get_external_status(global_driver); + kref_get(&global_driver->refcnt); mutex_unlock(&uctrl_mutex); return 0; } @@ -224,6 +241,7 @@ static const struct file_operations uctrl_fops =3D { .llseek =3D no_llseek, .unlocked_ioctl =3D uctrl_ioctl, .open =3D uctrl_open, + .release =3D uctrl_close, }; =20 static struct miscdevice uctrl_dev =3D { @@ -404,10 +422,7 @@ static int uctrl_remove(struct platform_device *op) struct uctrl_driver *p =3D dev_get_drvdata(&op->dev); =20 if (p) { - misc_deregister(&uctrl_dev); - free_irq(p->irq, p); - of_iounmap(&op->resource[0], p->regs, resource_size(&op->resource[0])); - kfree(p); + kref_put(&p->refcnt, uctrl_delete); } return 0; } --=20 2.39.0