[syzbot] [media?] general protection fault in vidtv_mux_stop_thread

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 9b2ffa6148b1 Merge tag 'mtd/fixes-for-6.13-rc5' of git://g..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=10f0a2f8580000
kernel config: https://syzkaller.appspot.com/x/.config?x=c078001e66e4a17e
dashboard link: https://syzkaller.appspot.com/bug?extid=5e248227c80a3be8e96a
compiler: gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=168b890f980000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1562eadf980000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/c1d66e09941d/disk-9b2ffa61.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/8aa24ea0a81d/vmlinux-9b2ffa61.xz
kernel image: https://storage.googleapis.com/syzbot-assets/0d9c0b1e880a/bzImage-9b2ffa61.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+5e2482...@syzkaller.appspotmail.com

Oops: general protection fault, probably for non-canonical address 0xdffffc0000000025: 0000 [#1] PREEMPT SMP KASAN PTI
KASAN: null-ptr-deref in range [0x0000000000000128-0x000000000000012f]
CPU: 0 UID: 0 PID: 5842 Comm: syz-executor248 Not tainted 6.13.0-rc4-syzkaller-00012-g9b2ffa6148b1 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
RIP: 0010:vidtv_mux_stop_thread+0x26/0x80 drivers/media/test-drivers/vidtv/vidtv_mux.c:471
Code: 90 90 90 90 66 0f 1f 00 55 53 48 89 fb e8 82 2e c8 f9 48 8d bb 28 01 00 00 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <0f> b6 04 02 84 c0 74 02 7e 3b 0f b6 ab 28 01 00 00 31 ff 89 ee e8
RSP: 0018:ffffc90003f2faa8 EFLAGS: 00010202
RAX: dffffc0000000000 RBX: 0000000000000000 RCX: ffffffff87cfb125
RDX: 0000000000000025 RSI: ffffffff87d120ce RDI: 0000000000000128
RBP: ffff888029b8d220 R08: 0000000000000005 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000003 R12: ffff888029b8d188
R13: ffffffff8f590aa0 R14: ffffc9000581c5c8 R15: ffff888029a17710
FS: 00007f7eef5156c0(0000) GS:ffff8880b8600000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f7eef5e635c CR3: 0000000076ca6000 CR4: 00000000003526f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
vidtv_stop_streaming drivers/media/test-drivers/vidtv/vidtv_bridge.c:209 [inline]
vidtv_stop_feed+0x151/0x250 drivers/media/test-drivers/vidtv/vidtv_bridge.c:252
dmx_section_feed_stop_filtering+0x90/0x160 drivers/media/dvb-core/dvb_demux.c:1000
dvb_dmxdev_feed_stop.isra.0+0x1ee/0x270 drivers/media/dvb-core/dmxdev.c:486
dvb_dmxdev_filter_stop+0x22a/0x3a0 drivers/media/dvb-core/dmxdev.c:559
dvb_dmxdev_filter_free drivers/media/dvb-core/dmxdev.c:840 [inline]
dvb_demux_release+0x92/0x550 drivers/media/dvb-core/dmxdev.c:1246
__fput+0x3f8/0xb60 fs/file_table.c:450
task_work_run+0x14e/0x250 kernel/task_work.c:239
get_signal+0x1d3/0x2610 kernel/signal.c:2790
arch_do_signal_or_restart+0x90/0x7e0 arch/x86/kernel/signal.c:337
exit_to_user_mode_loop kernel/entry/common.c:111 [inline]
exit_to_user_mode_prepare include/linux/entry-common.h:329 [inline]
__syscall_exit_to_user_mode_work kernel/entry/common.c:207 [inline]
syscall_exit_to_user_mode+0x150/0x2a0 kernel/entry/common.c:218
do_syscall_64+0xda/0x250 arch/x86/entry/common.c:89
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f7eef55b309
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 e1 18 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f7eef515218 EFLAGS: 00000246 ORIG_RAX: 0000000000000013
RAX: fffffffffffffe00 RBX: 00007f7eef5e53e8 RCX: 00007f7eef55b309
RDX: 0000000000000009 RSI: 0000000020003080 RDI: 0000000000000003
RBP: 00007f7eef5e53e0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f7eef5b2280
R13: 00736d79736c6c61 R14: 616b2f636f72702f R15: 0000100000000008
</TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:vidtv_mux_stop_thread+0x26/0x80 drivers/media/test-drivers/vidtv/vidtv_mux.c:471
Code: 90 90 90 90 66 0f 1f 00 55 53 48 89 fb e8 82 2e c8 f9 48 8d bb 28 01 00 00 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <0f> b6 04 02 84 c0 74 02 7e 3b 0f b6 ab 28 01 00 00 31 ff 89 ee e8
RSP: 0018:ffffc90003f2faa8 EFLAGS: 00010202
RAX: dffffc0000000000 RBX: 0000000000000000 RCX: ffffffff87cfb125
RDX: 0000000000000025 RSI: ffffffff87d120ce RDI: 0000000000000128
RBP: ffff888029b8d220 R08: 0000000000000005 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000003 R12: ffff888029b8d188
R13: ffffffff8f590aa0 R14: ffffc9000581c5c8 R15: ffff888029a17710
FS: 00007f7eef5156c0(0000) GS:ffff8880b8600000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f7eef5e635c CR3: 0000000076ca6000 CR4: 00000000003526f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
----------------
Code disassembly (best guess):
0: 90 nop
1: 90 nop
2: 90 nop
3: 90 nop
4: 66 0f 1f 00 nopw (%rax)
8: 55 push %rbp
9: 53 push %rbx
a: 48 89 fb mov %rdi,%rbx
d: e8 82 2e c8 f9 call 0xf9c82e94
12: 48 8d bb 28 01 00 00 lea 0x128(%rbx),%rdi
19: 48 b8 00 00 00 00 00 movabs $0xdffffc0000000000,%rax
20: fc ff df
23: 48 89 fa mov %rdi,%rdx
26: 48 c1 ea 03 shr $0x3,%rdx
* 2a: 0f b6 04 02 movzbl (%rdx,%rax,1),%eax <-- trapping instruction
2e: 84 c0 test %al,%al
30: 74 02 je 0x34
32: 7e 3b jle 0x6f
34: 0f b6 ab 28 01 00 00 movzbl 0x128(%rbx),%ebp
3b: 31 ff xor %edi,%edi
3d: 89 ee mov %ebp,%esi
3f: e8 .byte 0xe8


---
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[Edward Adam Davis]

#syz test: https://github.com/ea1davis/linux md/syz

[syzbot]

Hello,

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

Reported-by: syzbot+5e2482...@syzkaller.appspotmail.com
Tested-by: syzbot+5e2482...@syzkaller.appspotmail.com

Tested on:

commit: 2c8e951c media: vidtv_bridge: Fix a null-ptr-deref in ..
git tree: https://github.com/ea1davis/linux md/syz
console output: https://syzkaller.appspot.com/x/log.txt?x=150b30b0580000
kernel config: https://syzkaller.appspot.com/x/.config?x=e8d97faf7b870c89

dashboard link: https://syzkaller.appspot.com/bug?extid=5e248227c80a3be8e96a
compiler: gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40

Note: no patches were applied.
Note: testing is done by a robot and is best-effort only.

[Edward Adam Davis]

syzbot report a null-ptr-deref in vidtv_mux_stop_thread. [1]

If dvb->mux is not initialized successfully by vidtv_mux_init() in the
vidtv_start_streaming(), it will trigger null pointer dereference about mux
in vidtv_mux_stop_thread().

Adjust the timing of streaming initialization and check it before
stopping it.

[1]

Reported-by: syzbot+5e2482...@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=5e248227c80a3be8e96a
Signed-off-by: Edward Adam Davis <ead...@qq.com>
---
drivers/media/test-drivers/vidtv/vidtv_bridge.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/media/test-drivers/vidtv/vidtv_bridge.c b/drivers/media/test-drivers/vidtv/vidtv_bridge.c
index e1dd8adeba46..438483c62fac 100644
--- a/drivers/media/test-drivers/vidtv/vidtv_bridge.c
+++ b/drivers/media/test-drivers/vidtv/vidtv_bridge.c
@@ -191,10 +191,11 @@ static int vidtv_start_streaming(struct vidtv_dvb *dvb)

mux_args.mux_buf_sz = mux_buf_sz;

- dvb->streaming = true;
dvb->mux = vidtv_mux_init(dvb->fe[0], dev, &mux_args);
if (!dvb->mux)
return -ENOMEM;
+
+ dvb->streaming = true;
vidtv_mux_start_thread(dvb->mux);

dev_dbg_ratelimited(dev, "Started streaming\n");
@@ -205,6 +206,11 @@ static int vidtv_stop_streaming(struct vidtv_dvb *dvb)
{
struct device *dev = &dvb->pdev->dev;

+ if (!dvb->streaming) {
+ dev_warn_ratelimited(dev, "No streaming. Skipping.\n");
+ return 0;
+ }
+
dvb->streaming = false;
vidtv_mux_stop_thread(dvb->mux);
vidtv_mux_destroy(dvb->mux);
--
2.47.0