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

[syzbot <syzbot+bd7c90de4c9f1f8ab660@syzkaller.appspotmail.com>]

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=135fa7fa580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=9682a42d8ec8b05c
dashboard link: https://syzkaller.appspot.com/bug?extid=bd7c90de4c9f1f8ab660
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=16db1402580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1481265a580000

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+bd7c90de4c9f1f8ab660@syzkaller.appspotmail.com

=====================================================
BUG: KMSAN: uninit-value in dvb_dmxdev_read_sec drivers/media/dvb-core/dmxdev.c:975 [inline]
BUG: KMSAN: uninit-value in dvb_demux_read+0x580/0xa40 drivers/media/dvb-core/dmxdev.c:1020
 dvb_dmxdev_read_sec drivers/media/dvb-core/dmxdev.c:975 [inline]
 dvb_demux_read+0x580/0xa40 drivers/media/dvb-core/dmxdev.c:1020
 do_loop_readv_writev fs/read_write.c:847 [inline]
 vfs_readv+0x931/0xf30 fs/read_write.c:1020
 do_preadv fs/read_write.c:1132 [inline]
 __do_sys_preadv fs/read_write.c:1179 [inline]
 __se_sys_preadv fs/read_write.c:1174 [inline]
 __x64_sys_preadv+0x2a3/0x510 fs/read_write.c:1174
 x64_sys_call+0x3033/0x3e70 arch/x86/include/generated/asm/syscalls_64.h:296
 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_dmxdev_init+0xd8/0x680 drivers/media/dvb-core/dmxdev.c:1417
 vidtv_bridge_dmxdev_init drivers/media/test-drivers/vidtv/vidtv_bridge.c:343 [inline]
 vidtv_bridge_dvb_init drivers/media/test-drivers/vidtv/vidtv_bridge.c:445 [inline]
 vidtv_bridge_probe+0x1bfd/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: 1 UID: 0 PID: 6063 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(voluntary) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/24/2026
=====================================================


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