[PATCH v2] drm/cirrus: fix a NULL vs IS_ERR() checks

[Shile Zhang]

The function drm_gem_shmem_vmap can returns error pointers as well,
which could cause following kernel crash:

BUG: unable to handle page fault for address: fffffffffffffffc
PGD 1426a12067 P4D 1426a12067 PUD 1426a14067 PMD 0
Oops: 0000 [#1] SMP NOPTI
CPU: 12 PID: 3598532 Comm: stress-ng Kdump: loaded Not tainted 5.10.50.x86_64 #1
...
RIP: 0010:memcpy_toio+0x23/0x50
Code: 00 00 00 00 0f 1f 00 0f 1f 44 00 00 48 85 d2 74 28 40 f6 c7 01 75 2b 48 83 fa 01 76 06 40 f6 c7 02 75 17 48 89 d1 48 c1 e9 02 <f3> a5 f6 c2 02 74 02 66 a5 f6 c2 01 74 01 a4 c3 66 a5 48 83 ea 02
RSP: 0018:ffffafbf8a203c68 EFLAGS: 00010216
RAX: 0000000000000000 RBX: fffffffffffffffc RCX: 0000000000000200
RDX: 0000000000000800 RSI: fffffffffffffffc RDI: ffffafbf82000000
RBP: ffffafbf82000000 R08: 0000000000000002 R09: 0000000000000000
R10: 00000000000002b5 R11: 0000000000000000 R12: 0000000000000800
R13: ffff8a6801099300 R14: 0000000000000001 R15: 0000000000000300
FS:  00007f4a6bc5f740(0000) GS:ffff8a8641900000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: fffffffffffffffc CR3: 00000016d3874001 CR4: 00000000003606e0
Call Trace:
 drm_fb_memcpy_dstclip+0x5e/0x80 [drm_kms_helper]
 cirrus_fb_blit_rect.isra.0+0xb7/0xe0 [cirrus]
 cirrus_pipe_update+0x9f/0xa8 [cirrus]
 drm_atomic_helper_commit_planes+0xb8/0x220 [drm_kms_helper]
 drm_atomic_helper_commit_tail+0x42/0x80 [drm_kms_helper]
 commit_tail+0xce/0x130 [drm_kms_helper]
 drm_atomic_helper_commit+0x113/0x140 [drm_kms_helper]
 drm_client_modeset_commit_atomic+0x1c4/0x200 [drm]
 drm_client_modeset_commit_locked+0x53/0x80 [drm]
 drm_client_modeset_commit+0x24/0x40 [drm]
 drm_fbdev_client_restore+0x48/0x85 [drm_kms_helper]
 drm_client_dev_restore+0x64/0xb0 [drm]
 drm_release+0xf2/0x110 [drm]
 __fput+0x96/0x240
 task_work_run+0x5c/0x90
 exit_to_user_mode_loop+0xce/0xd0
 exit_to_user_mode_prepare+0x6a/0x70
 syscall_exit_to_user_mode+0x12/0x40
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x7f4a6bd82c2b

Fixes: ab3e023b1b4c9 ("drm/cirrus: rewrite and modernize driver.")

Signed-off-by: Shile Zhang <shile.zhang@xxxxxxxxxxxxxxxxx>
---
v2: rebase to latest stable linux-5.10.y branch.
v1: https://lore.kernel.org/lkml/550e9439-adf6-3df8-41a0-9a7ee5447907@xxxxxxxxxxxxxxxxx/
---
 drivers/gpu/drm/tiny/cirrus.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/tiny/cirrus.c b/drivers/gpu/drm/tiny/cirrus.c
index 744a8e337e41e..d64f6bb767eeb 100644
--- a/drivers/gpu/drm/tiny/cirrus.c
+++ b/drivers/gpu/drm/tiny/cirrus.c
@@ -323,7 +323,7 @@ static int cirrus_fb_blit_rect(struct drm_framebuffer *fb,
 
 	ret = -ENOMEM;
 	vmap = drm_gem_shmem_vmap(fb->obj[0]);
-	if (!vmap)
+	if (IS_ERR_OR_NULL(vmap))
 		goto out_dev_exit;
 
 	if (cirrus->cpp == fb->format->cpp[0])
-- 
2.33.0.rc2