linux-kernel - [PATCH] gpiolib: cdev: Don't access uninitialized descriptor

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Date:   Fri,  8 Jul 2022 16:55:48 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <brgl@...ev.pl>,
        Dipen Patel <dipenp@...dia.com>,
        Thierry Reding <treding@...dia.com>
Cc:     Viresh Kumar <viresh.kumar@...aro.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] gpiolib: cdev: Don't access uninitialized descriptor

linereq_free() can be called from in the middle of errors, where the
descriptor may be NULL for few lines. Don't access uninitialized
descriptor pointer as it leads to kernel crash:

    Unable to handle kernel NULL pointer dereference at virtual address 0000000000000008

    [...]

    Call trace:
     linereq_free+0x54/0xb8
     linereq_create+0x424/0x570
     gpio_ioctl+0x94/0x640
     __arm64_sys_ioctl+0xac/0xf0
     invoke_syscall+0x44/0x100
     el0_svc_common.constprop.3+0x6c/0xf0
     do_el0_svc+0x2c/0xb8
     el0_svc+0x20/0x60
     el0t_64_sync_handler+0x98/0xc0
     el0t_64_sync+0x170/0x174

Fixes: 2068339a6c35 ("gpiolib: cdev: Add hardware timestamp clock type")
Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
---
 drivers/gpio/gpiolib-cdev.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/gpio/gpiolib-cdev.c b/drivers/gpio/gpiolib-cdev.c
index f5aa5f93342a..d3d1b5aed282 100644
--- a/drivers/gpio/gpiolib-cdev.c
+++ b/drivers/gpio/gpiolib-cdev.c
@@ -1460,11 +1460,13 @@ static ssize_t linereq_read(struct file *file,
 static void linereq_free(struct linereq *lr)
 {
 	unsigned int i;
-	bool hte;
+	bool hte = false;
 
 	for (i = 0; i < lr->num_lines; i++) {
-		hte = !!test_bit(FLAG_EVENT_CLOCK_HTE,
-				 &lr->lines[i].desc->flags);
+		if (lr->lines[i].desc) {
+			hte = !!test_bit(FLAG_EVENT_CLOCK_HTE,
+					 &lr->lines[i].desc->flags);
+		}
 		edge_detector_stop(&lr->lines[i], hte);
 		if (lr->lines[i].desc)
 			gpiod_free(lr->lines[i].desc);
-- 
2.31.1.272.g89b43f80a514