[PATCH 6.1.y 5.15.y] drm/shmem-helper: Fix BUG_ON() on mmap(PROT_WRITE, MAP_PRIVATE)

[PATCH 6.1.y 5.15.y] drm/shmem-helper: Fix BUG_ON() on mmap(PROT_WRITE, MAP_PRIVATE)

[Sherry Yang]

From: "Wachowski, Karol" <karol.wachowski@intel.com>

commit 39bc27bd688066a63e56f7f64ad34fae03fbe3b8 upstream.

Lack of check for copy-on-write (COW) mapping in drm_gem_shmem_mmap
allows users to call mmap with PROT_WRITE and MAP_PRIVATE flag
causing a kernel panic due to BUG_ON in vmf_insert_pfn_prot:
BUG_ON((vma->vm_flags & VM_PFNMAP) && is_cow_mapping(vma->vm_flags));

Return -EINVAL early if COW mapping is detected.

This bug affects all drm drivers using default shmem helpers.
It can be reproduced by this simple example:
void *ptr = mmap(0, size, PROT_WRITE, MAP_PRIVATE, fd, mmap_offset);
ptr[0] = 0;

Fixes: 2194a63a818d ("drm: Add library for shmem backed GEM objects")
Cc: Noralf Trønnes <noralf@tronnes.org>
Cc: Eric Anholt <eric@anholt.net>
Cc: Rob Herring <robh@kernel.org>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: David Airlie <airlied@gmail.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: dri-devel@lists.freedesktop.org
Cc: <stable@vger.kernel.org> # v5.2+
Signed-off-by: Wachowski, Karol <karol.wachowski@intel.com>
Signed-off-by: Jacek Lawrynowicz <jacek.lawrynowicz@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20240520100514.925681-1-jacek.lawrynowicz@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[Sherry: bp to fix CVE-2024-39497, ignore context change due to missing
commit 21aa27ddc582 ("drm/shmem-helper: Switch to reservation lock")]
Signed-off-by: Sherry Yang <sherry.yang@oracle.com>
---
 drivers/gpu/drm/drm_gem_shmem_helper.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
index e33f06bb66eb..fb8093577245 100644
--- a/drivers/gpu/drm/drm_gem_shmem_helper.c
+++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
@@ -638,6 +638,9 @@ int drm_gem_shmem_mmap(struct drm_gem_shmem_object *shmem, struct vm_area_struct
 		return ret;
 	}
 
+	if (is_cow_mapping(vma->vm_flags))
+		return -EINVAL;
+
 	ret = drm_gem_shmem_get_pages(shmem);
 	if (ret)
 		return ret;
-- 
2.46.0

Re: [PATCH 6.1.y 5.15.y] drm/shmem-helper: Fix BUG_ON() on mmap(PROT_WRITE, MAP_PRIVATE)

[Greg KH]

On Thu, Oct 17, 2024 at 10:18:29AM -0700, Sherry Yang wrote:
> From: "Wachowski, Karol" <karol.wachowski@intel.com>
> 
> commit 39bc27bd688066a63e56f7f64ad34fae03fbe3b8 upstream.

Now queued up, thanks.

greg k-h