drm/vkms: Fix use after free and double free on init error

If the driver initialization fails, the vkms_exit() function might
access an uninitialized or freed default_config pointer and it might
double free it.

Fix both possible errors by initializing default_config only when the
driver initialization succeeded.

Reported-by: Louis Chauvet <louis.chauvet@bootlin.com>
Closes: https://lore.kernel.org/all/Z5uDHcCmAwiTsGte@louis-chauvet-laptop/
Fixes: 2df7af93fdad ("drm/vkms: Add vkms_config type")
Signed-off-by: José Expósito <jose.exposito89@gmail.com>
Reviewed-by: Thomas Zimmermann <tzimmremann@suse.de>
Reviewed-by: Louis Chauvet <louis.chauvet@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250212084912.3196-1-jose.exposito89@gmail.com
Signed-off-by: Louis Chauvet <louis.chauvet@bootlin.com>

diff --git a/drivers/gpu/drm/vkms/vkms_drv.c b/drivers/gpu/drm/vkms/vkms_drv.c
index 7c142bfc3bd9de9556621db3e7f570dc0a4fab3a..b6de91134a225b1747b07f845906fc7da1a534f8 100644 (file)
--- a/drivers/gpu/drm/vkms/vkms_drv.c
+++ b/drivers/gpu/drm/vkms/vkms_drv.c
@@ -235,17 +235,19 @@ static int __init vkms_init(void)
        if (!config)
                return -ENOMEM;
 
-       default_config = config;
-
        config->cursor = enable_cursor;
        config->writeback = enable_writeback;
        config->overlay = enable_overlay;
 
        ret = vkms_create(config);
-       if (ret)
+       if (ret) {
                kfree(config);
+               return ret;
+       }
 
-       return ret;
+       default_config = config;
+
+       return 0;
 }
 
 static void vkms_destroy(struct vkms_config *config)
@@ -269,9 +271,10 @@ static void vkms_destroy(struct vkms_config *config)
 
 static void __exit vkms_exit(void)
 {
-       if (default_config->dev)
-               vkms_destroy(default_config);
+       if (!default_config)
+               return;
 
+       vkms_destroy(default_config);
        kfree(default_config);
 }