On Fri, Mar 11, 2022 at 07:23:02AM +0000, Zheyu Ma wrote:
The user program can control the 'drm_buf_desc::flags' via ioctl system call and enter the function drm_legacy_addbufs_agp(). If the driver doesn't initialize the agp resources, the driver will cause a null pointer dereference.
The following log reveals it: general protection fault, probably for non-canonical address 0xdffffc000000000f: 0000 [#1] PREEMPT SMP KASAN PTI KASAN: null-ptr-deref in range [0x0000000000000078-0x000000000000007f] Call Trace: <TASK> drm_ioctl_kernel+0x342/0x450 drivers/gpu/drm/drm_ioctl.c:785 drm_ioctl+0x592/0x940 drivers/gpu/drm/drm_ioctl.c:885 vfs_ioctl fs/ioctl.c:51 [inline] __do_sys_ioctl fs/ioctl.c:874 [inline] __se_sys_ioctl+0xaa/0xf0 fs/ioctl.c:860 do_syscall_x64 arch/x86/entry/common.c:50 [inline] do_syscall_64+0x43/0x90 arch/x86/entry/common.c:80 entry_SYSCALL_64_after_hwframe+0x44/0xae
Fix this bug by adding a check.
Signed-off-by: Zheyu Ma zheyuma97@gmail.com
You can only hit this if you enabled a DRIVER_LEGACY drm driver, which opens you up to tons of other CVEs and issues. What's your .config? -Daniel
drivers/gpu/drm/drm_bufs.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/drm_bufs.c b/drivers/gpu/drm/drm_bufs.c index fcca21e8efac..4fe2363b1e34 100644 --- a/drivers/gpu/drm/drm_bufs.c +++ b/drivers/gpu/drm/drm_bufs.c @@ -734,7 +734,7 @@ int drm_legacy_addbufs_agp(struct drm_device *dev, int i, valid; struct drm_buf **temp_buflist;
- if (!dma)
if (!dma || !dev->agp) return -EINVAL;
count = request->count;
-- 2.25.1