Re: [PATCH] drm/vkms: Fix use after free and double free on init error

[Thomas Zimmermann]

Am 12.02.25 um 09:49 schrieb José Expósito:

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.chau...@bootlin.com>
Link: https://lore.kernel.org/all/Z5uDHcCmAwiTsGte@louis-chauvet-laptop/
Fixes: 2df7af93fdad ("drm/vkms: Add vkms_config type")
Signed-off-by: José Expósito <jose.exposit...@gmail.com>

Reviewed-by: Thomas Zimmermann <tzimmrem...@suse.de>

Thanks for posting this patch separately.

Best regards
Thomas

---
  drivers/gpu/drm/vkms/vkms_drv.c | 15 +++++++++------
  1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/vkms/vkms_drv.c b/drivers/gpu/drm/vkms/vkms_drv.c
index 7c142bfc3bd9..b6de91134a22 100644
--- 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);
  }

--
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)