media: vimc: upon streaming, check that the pipeline starts with a source entity

Userspace can disable links and create pipelines that
do not start with a source entity. Trying to stream
from such a pipeline should fail with -EPIPE
currently this is not handled and cause kernel crash.

Reproducing the crash:
media-ctl -d0 -l "5:1->21:0[0]" -v
v4l2-ctl -z platform:vimc -d "RGB/YUV Capture" -v width=1920,height=1440
v4l2-ctl --stream-mmap --stream-count=100 -d /dev/video2

Panic message:
[   39.078841][  T248] BUG: kernel NULL pointer dereference, address: 0000000000000000
[   39.079338][  T248] #PF: supervisor read access in kernel mode
[   39.079704][  T248] #PF: error_code(0x0000) - not-present page
[   39.080071][  T248] PGD 0 P4D 0
[   39.080279][  T248] Oops: 0000 [#1] SMP PTI
[   39.080546][  T248] CPU: 0 PID: 248 Comm: vimc-streamer t Not tainted 5.4.0-rc1+ #17
[   39.081030][  T248] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.12.0-0-ga698c8995f-prebuilt.qemu.org 04/01/2014
[   39.081779][  T248] RIP: 0010:vimc_sca_process_frame+0xdb/0x210 [vimc]
[   39.082191][  T248] Code: 44 8d 0c 28 8b 93 a4 01 00 00 48 8b 8b 98 01 00 00 85 d2 74 40 48 8b 74 24 10 8d 7a ff 4c 01 c9 31 d2 4c 01 fe eb 03 4c 89 c2 <44> 0f b6 04 16 44 88 04 11 4c 8d 42 01 48 39 fa 75 eb 8b 93 a4 01
[   39.083436][  T248] RSP: 0018:ffffb15a005abe90 EFLAGS: 00010246
[   39.083808][  T248] RAX: 0000000000000000 RBX: ffffa3fdc46d2e00 RCX: ffffb15a02579000
[   39.084298][  T248] RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000002
[   39.084792][  T248] RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
[   39.085280][  T248] R10: 0000000000000001 R11: 0000000000000000 R12: 0000000000000000
[   39.085770][  T248] R13: ffffa3fdc46d2ee0 R14: 0000000000000000 R15: 0000000000000000
[   39.086258][  T248] FS:  0000000000000000(0000) GS:ffffa3fdc7800000(0000) knlGS:0000000000000000
[   39.086806][  T248] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   39.087217][  T248] CR2: 0000000000000000 CR3: 0000000003c92005 CR4: 0000000000360ef0
[   39.087706][  T248] Call Trace:
[   39.087909][  T248]  ? vimc_streamer_pipeline_terminate+0x90/0x90 [vimc]
[   39.088318][  T248]  vimc_streamer_thread+0x7c/0xe0 [vimc]
[   39.088663][  T248]  kthread+0x10d/0x130
[   39.088919][  T248]  ? kthread_park+0x80/0x80
[   39.089205][  T248]  ret_from_fork+0x35/0x40
[   39.089475][  T248] Modules linked in: vimc videobuf2_vmalloc videobuf2_memops v4l2_tpg videobuf2_v4l2 videobuf2_common videodev mc
[   39.090208][  T248] CR2: 0000000000000000
[   39.090463][  T248] ---[ end trace 697650fefbf78bee ]---
[   39.090796][  T248] RIP: 0010:vimc_sca_process_frame+0xdb/0x210 [vimc]
[   39.091209][  T248] Code: 44 8d 0c 28 8b 93 a4 01 00 00 48 8b 8b 98 01 00 00 85 d2 74 40 48 8b 74 24 10 8d 7a ff 4c 01 c9 31 d2 4c 01 fe eb 03 4c 89 c2 <44> 0f b6 04 16 44 88 04 11 4c 8d 42 01 48 39 fa 75 eb 8b 93 a4 01
[   39.092417][  T248] RSP: 0018:ffffb15a005abe90 EFLAGS: 00010246
[   39.092789][  T248] RAX: 0000000000000000 RBX: ffffa3fdc46d2e00 RCX: ffffb15a02579000
[   39.093278][  T248] RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000002
[   39.093766][  T248] RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
[   39.094254][  T248] R10: 0000000000000001 R11: 0000000000000000 R12: 0000000000000000
[   39.094742][  T248] R13: ffffa3fdc46d2ee0 R14: 0000000000000000 R15: 0000000000000000
[   39.095309][  T248] FS:  0000000000000000(0000) GS:ffffa3fdc7800000(0000) knlGS:0000000000000000
[   39.095974][  T248] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   39.096372][  T248] CR2: 0000000000000000 CR3: 0000000003c92005 CR4: 0000000000360ef0
Signed-off-by: Dafna Hirschfeld <dafna.hirschfeld@collabora.com>
Acked-by: Helen Koike <helen.koike@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>

drivers/media/platform/vimc/vimc-common.c

@@ -164,6 +164,16 @@ static const struct vimc_pix_map vimc_pix_map_list[] = {
 	},
 };
 
+bool vimc_is_source(struct media_entity *ent)
+{
+	unsigned int i;
+
+	for (i = 0; i < ent->num_pads; i++)
+		if (ent->pads[i].flags & MEDIA_PAD_FL_SINK)
+			return false;
+	return true;
+}
+
 const struct vimc_pix_map *vimc_pix_map_by_index(unsigned int i)
 {
 	if (i >= ARRAY_SIZE(vimc_pix_map_list))

drivers/media/platform/vimc/vimc-common.h

@@ -139,6 +139,14 @@ struct vimc_ent_config {
 	void (*rm)(struct vimc_device *vimc, struct vimc_ent_device *ved);
 };
 
+/**
+ * vimc_is_source - returns true if the entity has only source pads
+ *
+ * @ent: pointer to &struct media_entity
+ *
+ */
+bool vimc_is_source(struct media_entity *ent);
+
 /* prototypes for vimc_ent_config add and rm hooks */
 struct vimc_ent_device *vimc_cap_add(struct vimc_device *vimc,
 				     const char *vcfg_name);

drivers/media/platform/vimc/vimc-streamer.c

@@ -104,9 +104,18 @@ static int vimc_streamer_pipeline_init(struct vimc_stream *stream,
 		}
 
 		entity = vimc_get_source_entity(ved->ent);
-		/* Check if the end of the pipeline was reached*/
-		if (!entity)
+		/* Check if the end of the pipeline was reached */
+		if (!entity) {
+			/* the first entity of the pipe should be source only */
+			if (!vimc_is_source(ved->ent)) {
+				dev_err(ved->dev,
+					"first entity in the pipe '%s' is not a source\n",
+					ved->ent->name);
+				vimc_streamer_pipeline_terminate(stream);
+				return -EPIPE;
+			}
 			return 0;
+		}
 
 		/* Get the next device in the pipeline */
 		if (is_media_entity_v4l2_subdev(entity)) {