Re: [syzbot] [media?] KASAN: slab-use-after-free Read in dvb_frontend_release (3)
From: syzbot
Date: Fri Feb 20 2026 - 02:18:13 EST
Hello,
syzbot has tested the proposed patch but the reproducer is still triggering an issue:
KASAN: slab-use-after-free Read in dvb_device_open
==================================================================
BUG: KASAN: slab-use-after-free in instrument_atomic_read include/linux/instrumented.h:68 [inline]
BUG: KASAN: slab-use-after-free in atomic_read include/linux/atomic/atomic-instrumented.h:32 [inline]
BUG: KASAN: slab-use-after-free in refcount_read include/linux/refcount.h:170 [inline]
BUG: KASAN: slab-use-after-free in __refcount_add_not_zero include/linux/refcount.h:176 [inline]
BUG: KASAN: slab-use-after-free in __refcount_inc_not_zero include/linux/refcount.h:317 [inline]
BUG: KASAN: slab-use-after-free in refcount_inc_not_zero include/linux/refcount.h:335 [inline]
BUG: KASAN: slab-use-after-free in kref_get_unless_zero include/linux/kref.h:133 [inline]
BUG: KASAN: slab-use-after-free in dvb_device_open+0x117/0x590 drivers/media/dvb-core/dvbdev.c:99
Read of size 4 at addr ffff88802bb50010 by task syz.0.19/6537
CPU: 1 UID: 0 PID: 6537 Comm: syz.0.19 Not tainted syzkaller #0 PREEMPT_{RT,(full)}
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
Call Trace:
<TASK>
dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
print_address_description mm/kasan/report.c:378 [inline]
print_report+0xba/0x230 mm/kasan/report.c:482
kasan_report+0x117/0x150 mm/kasan/report.c:595
check_region_inline mm/kasan/generic.c:-1 [inline]
kasan_check_range+0x264/0x2c0 mm/kasan/generic.c:200
instrument_atomic_read include/linux/instrumented.h:68 [inline]
atomic_read include/linux/atomic/atomic-instrumented.h:32 [inline]
refcount_read include/linux/refcount.h:170 [inline]
__refcount_add_not_zero include/linux/refcount.h:176 [inline]
__refcount_inc_not_zero include/linux/refcount.h:317 [inline]
refcount_inc_not_zero include/linux/refcount.h:335 [inline]
kref_get_unless_zero include/linux/kref.h:133 [inline]
dvb_device_open+0x117/0x590 drivers/media/dvb-core/dvbdev.c:99
chrdev_open+0x4d0/0x5f0 fs/char_dev.c:411
do_dentry_open+0x83d/0x13e0 fs/open.c:949
vfs_open+0x3b/0x350 fs/open.c:1081
do_open fs/namei.c:4671 [inline]
path_openat+0x2e3d/0x38a0 fs/namei.c:4830
do_file_open+0x23e/0x4a0 fs/namei.c:4859
do_sys_openat2+0x113/0x200 fs/open.c:1366
do_sys_open fs/open.c:1372 [inline]
__do_sys_openat fs/open.c:1388 [inline]
__se_sys_openat fs/open.c:1383 [inline]
__x64_sys_openat+0x138/0x170 fs/open.c:1383
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f8a3bbbc84e
Code: 08 0f 85 a5 a8 ff ff 49 89 fb 48 89 f0 48 89 d7 48 89 ce 4c 89 c2 4d 89 ca 4c 8b 44 24 08 4c 8b 4c 24 10 4c 89 5c 24 08 0f 05 <c3> 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 80 00 00 00 00 48 83 ec 08
RSP: 002b:00007f8a3b25db28 EFLAGS: 00000246 ORIG_RAX: 0000000000000101
RAX: ffffffffffffffda RBX: 00007f8a3b25e6c0 RCX: 00007f8a3bbbc84e
RDX: 0000000000000400 RSI: 00007f8a3b25dc00 RDI: ffffffffffffff9c
RBP: 00007f8a3b25dc00 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: cccccccccccccccd
R13: 00007f8a3be76038 R14: 00007f8a3be75fa0 R15: 00007ffd6024f3a8
</TASK>
Allocated by task 1:
kasan_save_stack mm/kasan/common.c:57 [inline]
kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
poison_kmalloc_redzone mm/kasan/common.c:398 [inline]
__kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:415
kasan_kmalloc include/linux/kasan.h:263 [inline]
__kmalloc_cache_noprof+0x3a6/0x690 mm/slub.c:5297
kmalloc_noprof include/linux/slab.h:962 [inline]
kzalloc_noprof include/linux/slab.h:1204 [inline]
dvb_register_device+0x2fd/0x2210 drivers/media/dvb-core/dvbdev.c:477
dvb_register_frontend+0x665/0x970 drivers/media/dvb-core/dvb_frontend.c:3053
vidtv_bridge_dvb_init drivers/media/test-drivers/vidtv/vidtv_bridge.c:436 [inline]
vidtv_bridge_probe+0x9aa/0xf80 drivers/media/test-drivers/vidtv/vidtv_bridge.c:508
platform_probe+0xf9/0x190 drivers/base/platform.c:1446
call_driver_probe drivers/base/dd.c:-1 [inline]
really_probe+0x267/0xaf0 drivers/base/dd.c:661
__driver_probe_device+0x18c/0x320 drivers/base/dd.c:803
driver_probe_device+0x4f/0x240 drivers/base/dd.c:833
__driver_attach+0x349/0x640 drivers/base/dd.c:1227
bus_for_each_dev+0x23e/0x2c0 drivers/base/bus.c:383
bus_add_driver+0x348/0x670 drivers/base/bus.c:715
driver_register+0x23a/0x320 drivers/base/driver.c:249
vidtv_bridge_init+0x28/0x50 drivers/media/test-drivers/vidtv/vidtv_bridge.c:598
do_one_initcall+0x250/0x840 init/main.c:1378
do_initcall_level+0x104/0x190 init/main.c:1440
do_initcalls+0x59/0xa0 init/main.c:1456
kernel_init_freeable+0x2a6/0x3d0 init/main.c:1688
kernel_init+0x1d/0x1d0 init/main.c:1578
ret_from_fork+0x51e/0xb90 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
Freed by task 6534:
kasan_save_stack mm/kasan/common.c:57 [inline]
kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
kasan_save_free_info+0x46/0x50 mm/kasan/generic.c:584
poison_slab_object mm/kasan/common.c:253 [inline]
__kasan_slab_free+0x5c/0x80 mm/kasan/common.c:285
kasan_slab_free include/linux/kasan.h:235 [inline]
slab_free_hook mm/slub.c:2670 [inline]
slab_free mm/slub.c:6082 [inline]
kfree+0x1c1/0x690 mm/slub.c:6399
dvb_frontend_release+0x3de/0x500 drivers/media/dvb-core/dvb_frontend.c:2935
__fput+0x45e/0xa80 fs/file_table.c:469
task_work_run+0x1d9/0x270 kernel/task_work.c:233
get_signal+0x11c3/0x1310 kernel/signal.c:2807
arch_do_signal_or_restart+0xbc/0x830 arch/x86/kernel/signal.c:337
__exit_to_user_mode_loop kernel/entry/common.c:64 [inline]
exit_to_user_mode_loop+0x86/0x480 kernel/entry/common.c:98
__exit_to_user_mode_prepare include/linux/irq-entry-common.h:226 [inline]
syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:256 [inline]
syscall_exit_to_user_mode include/linux/entry-common.h:325 [inline]
do_syscall_64+0x32d/0xf80 arch/x86/entry/syscall_64.c:100
entry_SYSCALL_64_after_hwframe+0x77/0x7f
The buggy address belongs to the object at ffff88802bb50000
which belongs to the cache kmalloc-512 of size 512
The buggy address is located 16 bytes inside of
freed 512-byte region [ffff88802bb50000, ffff88802bb50200)
The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x2bb50
head: order:2 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
flags: 0x80000000000040(head|node=0|zone=1)
page_type: f5(slab)
raw: 0080000000000040 ffff88813fe0dc80 dead000000000100 dead000000000122
raw: 0000000000000000 0000000000100010 00000000f5000000 0000000000000000
head: 0080000000000040 ffff88813fe0dc80 dead000000000100 dead000000000122
head: 0000000000000000 0000000000100010 00000000f5000000 0000000000000000
head: 0080000000000002 ffffea0000aed401 00000000ffffffff 00000000ffffffff
head: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000004
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 2, migratetype Unmovable, gfp_mask 0xd20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 1, tgid 1 (swapper/0), ts 14383756285, free_ts 0
set_page_owner include/linux/page_owner.h:32 [inline]
post_alloc_hook+0x228/0x280 mm/page_alloc.c:1884
prep_new_page mm/page_alloc.c:1892 [inline]
get_page_from_freelist+0x28bb/0x2950 mm/page_alloc.c:3950
__alloc_frozen_pages_noprof+0x18d/0x380 mm/page_alloc.c:5245
alloc_slab_page mm/slub.c:3238 [inline]
allocate_slab+0x77/0x660 mm/slub.c:3411
new_slab mm/slub.c:3469 [inline]
refill_objects+0x334/0x3c0 mm/slub.c:7091
refill_sheaf mm/slub.c:2787 [inline]
__pcs_replace_empty_main+0x328/0x5f0 mm/slub.c:4536
alloc_from_pcs mm/slub.c:4639 [inline]
slab_alloc_node mm/slub.c:4773 [inline]
__kmalloc_cache_noprof+0x44e/0x690 mm/slub.c:5292
kmalloc_noprof include/linux/slab.h:962 [inline]
kzalloc_noprof include/linux/slab.h:1204 [inline]
device_private_init drivers/base/core.c:3534 [inline]
device_add+0xbe/0xb80 drivers/base/core.c:3585
platform_device_add+0x46a/0x800 drivers/base/platform.c:757
vidtv_bridge_init+0x12/0x50 drivers/media/test-drivers/vidtv/vidtv_bridge.c:594
do_one_initcall+0x250/0x840 init/main.c:1378
do_initcall_level+0x104/0x190 init/main.c:1440
do_initcalls+0x59/0xa0 init/main.c:1456
kernel_init_freeable+0x2a6/0x3d0 init/main.c:1688
kernel_init+0x1d/0x1d0 init/main.c:1578
ret_from_fork+0x51e/0xb90 arch/x86/kernel/process.c:158
page_owner free stack trace missing
Memory state around the buggy address:
ffff88802bb4ff00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffff88802bb4ff80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff88802bb50000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff88802bb50080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff88802bb50100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================
Tested on:
commit: c22e26bd Merge tag 'landlock-7.0-rc1' of git://git.ker..
git tree: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
console output: https://syzkaller.appspot.com/x/log.txt?x=16c73c02580000
kernel config: https://syzkaller.appspot.com/x/.config?x=6428d17febdfb14e
dashboard link: https://syzkaller.appspot.com/bug?extid=ae466a728017ec940b41
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=15f7195a580000