From: "Wachowski, Karol" <karol.wachowski@xxxxxxxxx>
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@xxxxxxxxxxx>
Cc: Eric Anholt <eric@xxxxxxxxxx>
Cc: Rob Herring <robh@xxxxxxxxxx>
Cc: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx>
Cc: Maxime Ripard <mripard@xxxxxxxxxx>
Cc: Thomas Zimmermann <tzimmermann@xxxxxxx>
Cc: David Airlie <airlied@xxxxxxxxx>
Cc: Daniel Vetter <daniel@xxxxxxxx>
Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx
Cc: <stable@xxxxxxxxxxxxxxx> # v5.2+
Signed-off-by: Wachowski, Karol <karol.wachowski@xxxxxxxxx>
Signed-off-by: Jacek Lawrynowicz <jacek.lawrynowicz@xxxxxxxxxxxxxxx>
---
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 177773bcdbfd..885a62c2e1be 100644
--- a/drivers/gpu/drm/drm_gem_shmem_helper.c
+++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
@@ -611,6 +611,9 @@ 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;
+
dma_resv_lock(shmem->base.resv, NULL);
ret = drm_gem_shmem_get_pages(shmem);
dma_resv_unlock(shmem->base.resv);
--
2.45.1
