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    Subject[PATCH 5.17 140/158] fbdev: Prevent possible use-after-free in fb_release()
    Date
    From: Daniel Vetter <daniel.vetter@ffwll.ch>

    [ Upstream commit 89bfd4017e58faaf70411555e7f508495114e90b ]

    Most fbdev drivers have issues with the fb_info lifetime, because call to
    framebuffer_release() from their driver's .remove callback, rather than
    doing from fbops.fb_destroy callback.

    Doing that will destroy the fb_info too early, while references to it may
    still exist, leading to a use-after-free error.

    To prevent this, check the fb_info reference counter when attempting to
    kfree the data structure in framebuffer_release(). That will leak it but
    at least will prevent the mentioned error.

    Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
    Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
    Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
    Link: https://patchwork.freedesktop.org/patch/msgid/20220505220413.365977-1-javierm@redhat.com
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    drivers/video/fbdev/core/fbsysfs.c | 4 ++++
    1 file changed, 4 insertions(+)

    diff --git a/drivers/video/fbdev/core/fbsysfs.c b/drivers/video/fbdev/core/fbsysfs.c
    index 26892940c213..82e31a2d845e 100644
    --- a/drivers/video/fbdev/core/fbsysfs.c
    +++ b/drivers/video/fbdev/core/fbsysfs.c
    @@ -80,6 +80,10 @@ void framebuffer_release(struct fb_info *info)
    {
    if (!info)
    return;
    +
    + if (WARN_ON(refcount_read(&info->count)))
    + return;
    +
    kfree(info->apertures);
    kfree(info);
    }
    --
    2.35.1


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