Patch "drm/shmem-helper: Fix BUG_ON() on mmap(PROT_WRITE, MAP_PRIVATE)" has been added to the 6.6-stable tree

[gregkh at linuxfoundation.org]

This is a note to let you know that I've just added the patch titled

    drm/shmem-helper: Fix BUG_ON() on mmap(PROT_WRITE, MAP_PRIVATE)

to the 6.6-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     drm-shmem-helper-fix-bug_on-on-mmap-prot_write-map_private.patch
and it can be found in the queue-6.6 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable at vger.kernel.org> know about it.


>From 39bc27bd688066a63e56f7f64ad34fae03fbe3b8 Mon Sep 17 00:00:00 2001
From: "Wachowski, Karol" <karol.wachowski at intel.com>
Date: Mon, 20 May 2024 12:05:14 +0200
Subject: drm/shmem-helper: Fix BUG_ON() on mmap(PROT_WRITE, MAP_PRIVATE)
MIME-Version: 1.0
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From: Wachowski, Karol <karol.wachowski at 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 at tronnes.org>
Cc: Eric Anholt <eric at anholt.net>
Cc: Rob Herring <robh at kernel.org>
Cc: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
Cc: Maxime Ripard <mripard at kernel.org>
Cc: Thomas Zimmermann <tzimmermann at suse.de>
Cc: David Airlie <airlied at gmail.com>
Cc: Daniel Vetter <daniel at ffwll.ch>
Cc: dri-devel at lists.freedesktop.org
Cc: <stable at vger.kernel.org> # v5.2+
Signed-off-by: Wachowski, Karol <karol.wachowski at intel.com>
Signed-off-by: Jacek Lawrynowicz <jacek.lawrynowicz at linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter at ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20240520100514.925681-1-jacek.lawrynowicz@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
---
 drivers/gpu/drm/drm_gem_shmem_helper.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/drivers/gpu/drm/drm_gem_shmem_helper.c
+++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
@@ -610,6 +610,9 @@ int drm_gem_shmem_mmap(struct drm_gem_sh
 		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);


Patches currently in stable-queue which might be from karol.wachowski at intel.com are

queue-6.6/drm-shmem-helper-fix-bug_on-on-mmap-prot_write-map_private.patch