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From: saeed.mirzamohammadi@oracle.com
To: linux-kernel@vger.kernel.org
Cc: b.zolnierkie@samsung.com, akpm@linux-foundation.org,
	rppt@kernel.org, daniel.vetter@ffwll.ch, jani.nikula@intel.com,
	gustavoars@kernel.org, dri-devel@lists.freedesktop.org,
	linux-fbdev@vger.kernel.org
Subject: [PATCH 1/1] video: fbdev: fix divide error in fbcon_switch
Date: Wed, 21 Oct 2020 16:57:58 -0700	[thread overview]
Message-ID: <20201021235758.59993-1-saeed.mirzamohammadi@oracle.com> (raw)

From: Saeed Mirzamohammadi <saeed.mirzamohammadi@oracle.com>

This patch fixes the issue due to:

[   89.572883] divide_error: 0000 [#1] SMP KASAN PTI
[   89.572897] CPU: 3 PID: 16083 Comm: repro Not tainted 5.9.0-rc7.20200930.rc1.allarch-19-g3e32d0d.syzk #5
[   89.572902] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 0.5.1 01/01/2011
[   89.572934] RIP: 0010:cirrusfb_check_var+0x84/0x1260

The error happens when the pixels value is calculated before performing the sanity checks on bits_per_pixel.
A bits_per_pixel set to zero causes divide by zero error.

This patch moves the calculation after the sanity check.

Signed-off-by: Saeed Mirzamohammadi <saeed.mirzamohammadi@oracle.com>
Tested-by: Saeed Mirzamohammadi <saeed.mirzamohammadi@oracle.com>
---
 drivers/video/fbdev/cirrusfb.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/video/fbdev/cirrusfb.c b/drivers/video/fbdev/cirrusfb.c
index 15a9ee7cd734..a7749101b094 100644
--- a/drivers/video/fbdev/cirrusfb.c
+++ b/drivers/video/fbdev/cirrusfb.c
@@ -531,7 +531,7 @@ static int cirrusfb_check_var(struct fb_var_screeninfo *var,
 {
 	int yres;
 	/* memory size in pixels */
-	unsigned pixels = info->screen_size * 8 / var->bits_per_pixel;
+	unsigned int pixels;
 	struct cirrusfb_info *cinfo = info->par;
 
 	switch (var->bits_per_pixel) {
@@ -573,6 +573,7 @@ static int cirrusfb_check_var(struct fb_var_screeninfo *var,
 		return -EINVAL;
 	}
 
+	pixels = info->screen_size * 8 / var->bits_per_pixel;
 	if (var->xres_virtual < var->xres)
 		var->xres_virtual = var->xres;
 	/* use highest possible virtual resolution */
-- 
2.27.0


WARNING: multiple messages have this Message-ID (diff)
From: saeed.mirzamohammadi@oracle.com
To: linux-kernel@vger.kernel.org
Cc: linux-fbdev@vger.kernel.org, b.zolnierkie@samsung.com,
	jani.nikula@intel.com, daniel.vetter@ffwll.ch,
	gustavoars@kernel.org, dri-devel@lists.freedesktop.org,
	akpm@linux-foundation.org, rppt@kernel.org
Subject: [PATCH 1/1] video: fbdev: fix divide error in fbcon_switch
Date: Wed, 21 Oct 2020 16:57:58 -0700	[thread overview]
Message-ID: <20201021235758.59993-1-saeed.mirzamohammadi@oracle.com> (raw)

From: Saeed Mirzamohammadi <saeed.mirzamohammadi@oracle.com>

This patch fixes the issue due to:

[   89.572883] divide_error: 0000 [#1] SMP KASAN PTI
[   89.572897] CPU: 3 PID: 16083 Comm: repro Not tainted 5.9.0-rc7.20200930.rc1.allarch-19-g3e32d0d.syzk #5
[   89.572902] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 0.5.1 01/01/2011
[   89.572934] RIP: 0010:cirrusfb_check_var+0x84/0x1260

The error happens when the pixels value is calculated before performing the sanity checks on bits_per_pixel.
A bits_per_pixel set to zero causes divide by zero error.

This patch moves the calculation after the sanity check.

Signed-off-by: Saeed Mirzamohammadi <saeed.mirzamohammadi@oracle.com>
Tested-by: Saeed Mirzamohammadi <saeed.mirzamohammadi@oracle.com>
---
 drivers/video/fbdev/cirrusfb.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/video/fbdev/cirrusfb.c b/drivers/video/fbdev/cirrusfb.c
index 15a9ee7cd734..a7749101b094 100644
--- a/drivers/video/fbdev/cirrusfb.c
+++ b/drivers/video/fbdev/cirrusfb.c
@@ -531,7 +531,7 @@ static int cirrusfb_check_var(struct fb_var_screeninfo *var,
 {
 	int yres;
 	/* memory size in pixels */
-	unsigned pixels = info->screen_size * 8 / var->bits_per_pixel;
+	unsigned int pixels;
 	struct cirrusfb_info *cinfo = info->par;
 
 	switch (var->bits_per_pixel) {
@@ -573,6 +573,7 @@ static int cirrusfb_check_var(struct fb_var_screeninfo *var,
 		return -EINVAL;
 	}
 
+	pixels = info->screen_size * 8 / var->bits_per_pixel;
 	if (var->xres_virtual < var->xres)
 		var->xres_virtual = var->xres;
 	/* use highest possible virtual resolution */
-- 
2.27.0

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             reply	other threads:[~2020-10-21 23:59 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-21 23:57 saeed.mirzamohammadi [this message]
2020-10-21 23:57 ` [PATCH 1/1] video: fbdev: fix divide error in fbcon_switch saeed.mirzamohammadi
2020-10-22  0:33 ` Saeed Mirzamohammadi
2020-10-22  0:33   ` Saeed Mirzamohammadi
2020-10-22  7:28 ` Thomas Zimmermann
2020-10-22  7:28   ` Thomas Zimmermann
2020-10-22  7:34 ` Thomas Zimmermann
2020-10-22  7:34   ` Thomas Zimmermann
2020-10-25 23:31   ` Saeed Mirzamohammadi
2020-10-26 17:00   ` Saeed Mirzamohammadi
2020-10-26 17:00     ` Saeed Mirzamohammadi
2020-10-27  6:22     ` Greg KH
2020-10-27  6:22       ` Greg KH
2020-10-27 16:22       ` Saeed Mirzamohammadi
2020-10-27 16:33       ` Saeed Mirzamohammadi
2020-10-27 17:12       ` Saeed Mirzamohammadi
2020-10-29 11:03         ` Greg KH
2020-10-29 11:03           ` Greg KH
2020-10-29 11:13           ` Jani Nikula
2020-10-29 11:13             ` Jani Nikula
2020-10-29 11:30             ` Greg KH
2020-10-29 11:30               ` Greg KH

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