[PATCH 6.6 066/452] drm, fbcon, vga_switcheroo: Avoid race condition in fbcon setup

6.6-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Thomas Zimmermann <[email protected]>

[ Upstream commit eb76d0f5553575599561010f24c277cc5b31d003 ]

Protect vga_switcheroo_client_fb_set() with console lock. Avoids OOB
access in fbcon_remap_all(). Without holding the console lock the call
races with switching outputs.

VGA switcheroo calls fbcon_remap_all() when switching clients. The fbcon
function uses struct fb_info.node, which is set by register_framebuffer().
As the fb-helper code currently sets up VGA switcheroo before registering
the framebuffer, the value of node is -1 and therefore not a legal value.
For example, fbcon uses the value within set_con2fb_map() [1] as an index
into an array.

Moving vga_switcheroo_client_fb_set() after register_framebuffer() can
result in VGA switching that does not switch fbcon correctly.

Therefore move vga_switcheroo_client_fb_set() under fbcon_fb_registered(),
which already holds the console lock. Fbdev calls fbcon_fb_registered()
from within register_framebuffer(). Serializes the helper with VGA
switcheroo's call to fbcon_remap_all().

Although vga_switcheroo_client_fb_set() takes an instance of struct fb_info
as parameter, it really only needs the contained fbcon state. Moving the
call to fbcon initialization is therefore cleaner than before. Only amdgpu,
i915, nouveau and radeon support vga_switcheroo. For all other drivers,
this change does nothing.

Signed-off-by: Thomas Zimmermann <[email protected]>
Link: https://elixir.bootlin.com/linux/v6.17/source/drivers/video/fbdev/core/fbcon.c#L2942 # [1]
Fixes: 6a9ee8af344e ("vga_switcheroo: initial implementation (v15)")
Acked-by: Javier Martinez Canillas <[email protected]>
Acked-by: Alex Deucher <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: <[email protected]> # v2.6.34+
Link: https://patch.msgid.link/[email protected]
[ Minor context conflict resolved. ]
Signed-off-by: Wenshan Lan <[email protected]>
Signed-off-by: Sasha Levin <[email protected]>
---
 drivers/gpu/drm/drm_fb_helper.c  | 14 --------------
 drivers/video/fbdev/core/fbcon.c |  9 +++++++++
 2 files changed, 9 insertions(+), 14 deletions(-)

diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
index eee7b56d441f71..9691c93f19a0dd 100644
--- a/drivers/gpu/drm/drm_fb_helper.c
+++ b/drivers/gpu/drm/drm_fb_helper.c
@@ -30,9 +30,7 @@
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 
 #include <linux/console.h>
-#include <linux/pci.h>
 #include <linux/sysrq.h>
-#include <linux/vga_switcheroo.h>
 
 #include <drm/drm_atomic.h>
 #include <drm/drm_drv.h>
@@ -575,11 +573,6 @@ EXPORT_SYMBOL(drm_fb_helper_release_info);
  */
 void drm_fb_helper_unregister_info(struct drm_fb_helper *fb_helper)
 {
-	struct fb_info *info = fb_helper->info;
-	struct device *dev = info->device;
-
-	if (dev_is_pci(dev))
-		vga_switcheroo_client_fb_set(to_pci_dev(dev), NULL);
 	unregister_framebuffer(fb_helper->info);
 }
 EXPORT_SYMBOL(drm_fb_helper_unregister_info);
@@ -1673,7 +1666,6 @@ static int drm_fb_helper_single_fb_probe(struct drm_fb_helper *fb_helper)
 {
 	struct drm_client_dev *client = &fb_helper->client;
 	struct drm_fb_helper_surface_size sizes;
-	struct fb_info *info;
 	int ret;
 
 	ret = drm_fb_helper_find_sizes(fb_helper, &sizes);
@@ -1691,12 +1683,6 @@ static int drm_fb_helper_single_fb_probe(struct drm_fb_helper *fb_helper)
 
 	strcpy(fb_helper->fb->comm, "[fbcon]");
 
-	info = fb_helper->info;
-
-	/* Set the fb info for vgaswitcheroo clients. Does nothing otherwise. */
-	if (dev_is_pci(info->device))
-		vga_switcheroo_client_fb_set(to_pci_dev(info->device), info);
-
 	return 0;
 }
 
diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c
index 703c4e851612c8..d1ac4e45eea68e 100644
--- a/drivers/video/fbdev/core/fbcon.c
+++ b/drivers/video/fbdev/core/fbcon.c
@@ -64,6 +64,7 @@
 #include <linux/console.h>
 #include <linux/string.h>
 #include <linux/kd.h>
+#include <linux/pci.h>
 #include <linux/slab.h>
 #include <linux/fb.h>
 #include <linux/fbcon.h>
@@ -75,6 +76,7 @@
 #include <linux/interrupt.h>
 #include <linux/crc32.h> /* For counting font checksums */
 #include <linux/uaccess.h>
+#include <linux/vga_switcheroo.h>
 #include <asm/irq.h>
 
 #include "fbcon.h"
@@ -2914,6 +2916,9 @@ void fbcon_fb_unregistered(struct fb_info *info)
 
 	console_lock();
 
+	if (info->device && dev_is_pci(info->device))
+		vga_switcheroo_client_fb_set(to_pci_dev(info->device), NULL);
+
 	fbcon_registered_fb[info->node] = NULL;
 	fbcon_num_registered_fb--;
 
@@ -3047,6 +3052,10 @@ static int do_fb_registered(struct fb_info *info)
 		}
 	}
 
+	/* Set the fb info for vga_switcheroo clients. Does nothing otherwise. */
+	if (info->device && dev_is_pci(info->device))
+		vga_switcheroo_client_fb_set(to_pci_dev(info->device), info);
+
 	return ret;
 }
 
-- 
2.53.0