[syzbot] [media?] KMSAN: uninit-value in dvbdmx_release_ts_feed

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 2687c848e578 x86/vmware: Fix hypercall clobbers
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16bd1402580000
kernel config: https://syzkaller.appspot.com/x/.config?x=9682a42d8ec8b05c
dashboard link: https://syzkaller.appspot.com/bug?extid=01d4620886bee3db0e74
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1154ab22580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1566fa5a580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/915713ca8484/disk-2687c848.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/9b87f40abe9d/vmlinux-2687c848.xz
kernel image: https://storage.googleapis.com/syzbot-assets/d4744727b418/bzImage-2687c848.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+01d462...@syzkaller.appspotmail.com

dvb_demux: dvb_demux_feed_del: feed not in list (type=0 state=0 pid=ffff)
=====================================================
BUG: KMSAN: uninit-value in dvbdmx_release_ts_feed+0x198/0x290 drivers/media/dvb-core/dvb_demux.c:858
dvbdmx_release_ts_feed+0x198/0x290 drivers/media/dvb-core/dvb_demux.c:858
dvb_dmxdev_start_feed drivers/media/dvb-core/dmxdev.c:-1 [inline]
dvb_dmxdev_filter_start+0x1187/0x1af0 drivers/media/dvb-core/dmxdev.c:766
dvb_dmxdev_pes_filter_set+0x810/0x860 drivers/media/dvb-core/dmxdev.c:963
dvb_demux_do_ioctl+0x9a3/0xc80 drivers/media/dvb-core/dmxdev.c:1077
dvb_usercopy+0x263/0x500 drivers/media/dvb-core/dvbdev.c:999
dvb_demux_ioctl+0x46/0x70 drivers/media/dvb-core/dmxdev.c:1186
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:597 [inline]
__se_sys_ioctl+0x23c/0x400 fs/ioctl.c:583
__x64_sys_ioctl+0x97/0xe0 fs/ioctl.c:583
x64_sys_call+0x18a7/0x3e70 arch/x86/include/generated/asm/syscalls_64.h:17
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xc9/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Uninit was created at:
__alloc_frozen_pages_noprof+0x6df/0xf50 mm/page_alloc.c:5263
alloc_pages_mpol+0x328/0x860 mm/mempolicy.c:2486
alloc_frozen_pages_noprof mm/mempolicy.c:2557 [inline]
alloc_pages_noprof+0x101/0x280 mm/mempolicy.c:2577
vm_area_alloc_pages mm/vmalloc.c:3649 [inline]
__vmalloc_area_node mm/vmalloc.c:3863 [inline]
__vmalloc_node_range_noprof+0xa97/0x2d80 mm/vmalloc.c:4051
__vmalloc_node_noprof mm/vmalloc.c:4111 [inline]
__vmalloc_noprof+0x128/0x1f0 mm/vmalloc.c:4127
__vmalloc_array_noprof mm/util.c:633 [inline]
vmalloc_array_noprof+0x48/0x80 mm/util.c:644
dvb_dmx_init+0x121/0x930 drivers/media/dvb-core/dvb_demux.c:1253
vidtv_bridge_dmx_init drivers/media/test-drivers/vidtv/vidtv_bridge.c:334 [inline]
vidtv_bridge_dvb_init drivers/media/test-drivers/vidtv/vidtv_bridge.c:441 [inline]
vidtv_bridge_probe+0x1b1f/0x2690 drivers/media/test-drivers/vidtv/vidtv_bridge.c:508
platform_probe+0x213/0x370 drivers/base/platform.c:1446
call_driver_probe drivers/base/dd.c:-1 [inline]
really_probe+0x4d5/0xe40 drivers/base/dd.c:661
__driver_probe_device+0x25e/0x370 drivers/base/dd.c:803
driver_probe_device+0x70/0x8f0 drivers/base/dd.c:833
__driver_attach+0x53e/0xaa0 drivers/base/dd.c:1227
bus_for_each_dev+0x33b/0x580 drivers/base/bus.c:383
driver_attach+0x51/0x70 drivers/base/dd.c:1245
bus_add_driver+0x54f/0xdb0 drivers/base/bus.c:715
driver_register+0x42e/0x6a0 drivers/base/driver.c:249
__platform_driver_register+0x65/0x80 drivers/base/platform.c:908
vidtv_bridge_init+0x73/0x100 drivers/media/test-drivers/vidtv/vidtv_bridge.c:598
do_one_initcall+0x22b/0xad0 init/main.c:1378
do_initcall_level+0x157/0x2e0 init/main.c:1440
do_initcalls+0x176/0x310 init/main.c:1456
do_basic_setup+0x1d/0x30 init/main.c:1475
kernel_init_freeable+0x213/0x430 init/main.c:1688
kernel_init+0x2f/0x5e0 init/main.c:1578
ret_from_fork+0x207/0x6f0 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246

CPU: 0 UID: 0 PID: 6181 Comm: syz.1.40 Not tainted syzkaller #0 PREEMPT(voluntary)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/24/2026
=====================================================


---
This report is generated by a bot. It may contain errors.
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If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
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If you want to undo deduplication, reply with:
#syz undup

[Edward Adam Davis]

#syz test

diff --git a/drivers/media/dvb-core/dvb_demux.c b/drivers/media/dvb-core/dvb_demux.c
index 290fc7961647..669ce8b95ad5 100644
--- a/drivers/media/dvb-core/dvb_demux.c
+++ b/drivers/media/dvb-core/dvb_demux.c
@@ -670,18 +670,22 @@ static void dvb_demux_feed_add(struct dvb_demux_feed *feed)
spin_unlock_irq(&feed->demux->lock);
}

-static void dvb_demux_feed_del(struct dvb_demux_feed *feed)
+static int dvb_demux_feed_del(struct dvb_demux_feed *feed)
{
+ int ret;
spin_lock_irq(&feed->demux->lock);
if (!(dvb_demux_feed_find(feed))) {
pr_err("%s: feed not in list (type=%x state=%x pid=%x)\n",
__func__, feed->type, feed->state, feed->pid);
+ ret = -EINVAL;
goto out;
}

list_del(&feed->list_head);
+ ret = 0;
out:
spin_unlock_irq(&feed->demux->lock);
+ return ret;
}

static int dmx_ts_feed_set(struct dmx_ts_feed *ts_feed, u16 pid, int ts_type,
@@ -840,6 +844,7 @@ static int dvbdmx_release_ts_feed(struct dmx_demux *dmx,
{
struct dvb_demux *demux = (struct dvb_demux *)dmx;
struct dvb_demux_feed *feed = (struct dvb_demux_feed *)ts_feed;
+ int ret;

mutex_lock(&demux->mutex);

@@ -851,11 +856,12 @@ static int dvbdmx_release_ts_feed(struct dmx_demux *dmx,
feed->state = DMX_STATE_FREE;
feed->filter->state = DMX_STATE_FREE;

- dvb_demux_feed_del(feed);
+ ret = dvb_demux_feed_del(feed);

feed->pid = 0xffff;

- if (feed->ts_type & TS_DECODER && feed->pes_type < DMX_PES_OTHER)
+ if (!ret && feed->ts_type & TS_DECODER &&
+ feed->pes_type < DMX_PES_OTHER)
demux->pesfilter[feed->pes_type] = NULL;

mutex_unlock(&demux->mutex);

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+01d462...@syzkaller.appspotmail.com
Tested-by: syzbot+01d462...@syzkaller.appspotmail.com

Tested on:

commit: e7aa5724 Merge tag 'spi-fix-v6.19-rc8' of git://git.ke..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=14e52a52580000

kernel config: https://syzkaller.appspot.com/x/.config?x=9682a42d8ec8b05c
dashboard link: https://syzkaller.appspot.com/bug?extid=01d4620886bee3db0e74
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8

patch: https://syzkaller.appspot.com/x/patch.diff?x=13179402580000

Note: testing is done by a robot and is best-effort only.

[Edward Adam Davis]

syzbot reported a uninit-value bug in [1].

When dmx_ts_feed_set() fails, the feed is not properly initialized. This
includes the feed not being added to the demux's feed_list and ts_type,
pes_type, etc., not being set. Under these circumstances, it is illogical
to determine whether to set the pesfilter in dvbdmx_release_ts_feed()
based on the uninitialized members ts_type and pes_type of the feed.

Since dvb_demux_feed_del() checks whether the feed has been successfully
added to the demux's feed_list, it can be confirmed that the feed has
been correctly initialized when it is added to the demux's feed_list.
A return value is added to dvb_demux_feed_del().
When the feed is not added to the feed_list, it is considered that the
feed has not yet been initialized, and when releasing the feed, it will
no longer determine whether to update the pesfilter based on its members.

[1]

BUG: KMSAN: uninit-value in dvbdmx_release_ts_feed+0x198/0x290 drivers/media/dvb-core/dvb_demux.c:858
dvbdmx_release_ts_feed+0x198/0x290 drivers/media/dvb-core/dvb_demux.c:858
dvb_dmxdev_start_feed drivers/media/dvb-core/dmxdev.c:-1 [inline]
dvb_dmxdev_filter_start+0x1187/0x1af0 drivers/media/dvb-core/dmxdev.c:766

Uninit was created at:

dvb_dmx_init+0x121/0x930 drivers/media/dvb-core/dvb_demux.c:1253
vidtv_bridge_dmx_init drivers/media/test-drivers/vidtv/vidtv_bridge.c:334 [inline]

Reported-by: syzbot+01d462...@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=01d4620886bee3db0e74
Tested-by: syzbot+01d462...@syzkaller.appspotmail.com
Signed-off-by: Edward Adam Davis <ead...@qq.com>
---
drivers/media/dvb-core/dvb_demux.c | 12 +++++++++---
1 file changed, 9 insertions(+), 3 deletions(-)

--
2.43.0

[syzbot]

For archival purposes, forwarding an incoming command email to
linux-...@vger.kernel.org, syzkall...@googlegroups.com.

***

Subject: [PATCH] media: dvb-core: fix uninit-value in dvbdmx_release_ts_feed()
Author: suun...@gmail.com

dvb_dmx_init() allocates feed and filter arrays with vmalloc_array(),
which does not initialize the allocated memory. If an error occurs during
dvb_dmxdev_start_feed() and dvbdmx_release_ts_feed() is called on a feed
that was never properly set up, dvbdmx_release_ts_feed() reads
uninitialized fields from the feed structure, triggering a KMSAN
uninit-value warning.

Fix this by using vcalloc() instead of vmalloc_array() to ensure the
structures are zero-initialized at allocation time.

Reported-by: syzbot+01d462...@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=01d4620886bee3db0e74

Fixes: e4b21577b463 ("media: dvb-core: use vmalloc_array to simplify code")
Signed-off-by: SeungJu Cheon <suun...@gmail.com>
---
#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master

drivers/media/dvb-core/dvb_demux.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/media/dvb-core/dvb_demux.c b/drivers/media/dvb-core/dvb_demux.c
index 290fc7961647..5c046db122ea 100644
--- a/drivers/media/dvb-core/dvb_demux.c
+++ b/drivers/media/dvb-core/dvb_demux.c
@@ -1244,13 +1244,13 @@ int dvb_dmx_init(struct dvb_demux *dvbdemux)

dvbdemux->cnt_storage = NULL;
dvbdemux->users = 0;
- dvbdemux->filter = vmalloc_array(dvbdemux->filternum,
+ dvbdemux->filter = vcalloc(dvbdemux->filternum,
sizeof(struct dvb_demux_filter));

if (!dvbdemux->filter)
return -ENOMEM;

- dvbdemux->feed = vmalloc_array(dvbdemux->feednum,
+ dvbdemux->feed = vcalloc(dvbdemux->feednum,
sizeof(struct dvb_demux_feed));
if (!dvbdemux->feed) {
vfree(dvbdemux->filter);
--
2.52.0

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+01d462...@syzkaller.appspotmail.com
Tested-by: syzbot+01d462...@syzkaller.appspotmail.com

Tested on:

commit: e7aa5724 Merge tag 'spi-fix-v6.19-rc8' of git://git.ke..
git tree: upstream

console output: https://syzkaller.appspot.com/x/log.txt?x=14605402580000

kernel config: https://syzkaller.appspot.com/x/.config?x=9682a42d8ec8b05c
dashboard link: https://syzkaller.appspot.com/bug?extid=01d4620886bee3db0e74
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8

patch: https://syzkaller.appspot.com/x/patch.diff?x=119ab65a580000