On 5/26/22 21:47, Javier Martinez Canillas wrote:
> Commit b3c9a924aab6 ("fbdev: vesafb: Cleanup fb_info in .fb_destroy rather
> than .remove") fixed a use-after-free error due the vesafb driver freeing
> the fb_info in the .remove handler instead of doing it in .fb_destroy.
>
> This can happen if the .fb_destroy callback is executed after the .remove
> callback, since the former tries to access a pointer freed by the latter.
>
> But that change didn't take into account that another possible scenario is
> that .fb_destroy is called before the .remove callback. For example, if no
> process has the fbdev chardev opened by the time the driver is removed.
>
> If that's the case, fb_info will be freed when unregister_framebuffer() is
> called, making the fb_info pointer accessed in vesafb_remove() after that
> to no longer be valid.
>
> To prevent that, move the expression containing the info->par to happen
> before the unregister_framebuffer() function call.
>
> Fixes: b3c9a924aab6 ("fbdev: vesafb: Cleanup fb_info in .fb_destroy rather
> than .remove")
> Reported-by: Pascal Ernster <[email protected]>
> Signed-off-by: Javier Martinez Canillas <[email protected]>
applied to the fbdev git tree.
Thanks!
Helge
> ---
>
> drivers/video/fbdev/vesafb.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/video/fbdev/vesafb.c b/drivers/video/fbdev/vesafb.c
> index e25e8de5ff67..929d4775cb4b 100644
> --- a/drivers/video/fbdev/vesafb.c
> +++ b/drivers/video/fbdev/vesafb.c
> @@ -490,11 +490,12 @@ static int vesafb_remove(struct platform_device *pdev)
> {
> struct fb_info *info = platform_get_drvdata(pdev);
>
> - /* vesafb_destroy takes care of info cleanup */
> - unregister_framebuffer(info);
> if (((struct vesafb_par *)(info->par))->region)
> release_region(0x3c0, 32);
>
> + /* vesafb_destroy takes care of info cleanup */
> + unregister_framebuffer(info);
> +
> return 0;
> }
>
