[syzbot] [ppp?] KMSAN: uninit-value in ppp_async_push (3)

Hello,

syzbot found the following issue on:

HEAD commit:    614da38e2f7a Merge tag 'hid-for-linus-2024051401' of git:/..
git tree:       upstream
console+strace: https://syzkaller.appspot.com/x/log.txt?x=1315203c980000
kernel config:  https://syzkaller.appspot.com/x/.config?x=f5d2cbf33633f507
dashboard link: https://syzkaller.appspot.com/bug?extid=ec0723ba9605678b14bf
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=14b284e8980000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1653d768980000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/89eafb874b71/disk-614da38e.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/356000512ad9/vmlinux-614da38e.xz
kernel image: https://storage.googleapis.com/syzbot-assets/839c73939115/bzImage-614da38e.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: [email protected]

=====================================================
BUG: KMSAN: uninit-value in ppp_async_encode drivers/net/ppp/ppp_async.c:548 [inline]
BUG: KMSAN: uninit-value in ppp_async_push+0xc05/0x2660 drivers/net/ppp/ppp_async.c:675
 ppp_async_encode drivers/net/ppp/ppp_async.c:548 [inline]
 ppp_async_push+0xc05/0x2660 drivers/net/ppp/ppp_async.c:675
 ppp_async_send+0x130/0x1b0 drivers/net/ppp/ppp_async.c:634
 ppp_push+0x220/0x22b0 drivers/net/ppp/ppp_generic.c:1883
 ppp_send_frame drivers/net/ppp/ppp_generic.c:1846 [inline]
 __ppp_xmit_process+0x123a/0x2780 drivers/net/ppp/ppp_generic.c:1646
 ppp_xmit_process+0x100/0x2b0 drivers/net/ppp/ppp_generic.c:1667
 ppp_write+0x63a/0x7d0 drivers/net/ppp/ppp_generic.c:521
 do_loop_readv_writev fs/read_write.c:764 [inline]
 vfs_writev+0xb0e/0x1450 fs/read_write.c:973
 do_pwritev fs/read_write.c:1072 [inline]
 __do_sys_pwritev fs/read_write.c:1119 [inline]
 __se_sys_pwritev fs/read_write.c:1114 [inline]
 __x64_sys_pwritev+0x2e5/0x500 fs/read_write.c:1114
 x64_sys_call+0x3539/0x3b50 arch/x86/include/generated/asm/syscalls_64.h:297
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xcf/0x1e0 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Uninit was created at:
 slab_post_alloc_hook mm/slub.c:3877 [inline]
 slab_alloc_node mm/slub.c:3918 [inline]
 kmem_cache_alloc_node+0x622/0xc90 mm/slub.c:3961
 kmalloc_reserve+0x13d/0x4a0 net/core/skbuff.c:577
 __alloc_skb+0x35b/0x7a0 net/core/skbuff.c:668
 alloc_skb include/linux/skbuff.h:1319 [inline]
 ppp_write+0xe5/0x7d0 drivers/net/ppp/ppp_generic.c:509
 do_loop_readv_writev fs/read_write.c:764 [inline]
 vfs_writev+0xb0e/0x1450 fs/read_write.c:973
 do_pwritev fs/read_write.c:1072 [inline]
 __do_sys_pwritev fs/read_write.c:1119 [inline]
 __se_sys_pwritev fs/read_write.c:1114 [inline]
 __x64_sys_pwritev+0x2e5/0x500 fs/read_write.c:1114
 x64_sys_call+0x3539/0x3b50 arch/x86/include/generated/asm/syscalls_64.h:297
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xcf/0x1e0 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

CPU: 1 PID: 5049 Comm: syz-executor420 Not tainted 6.9.0-syzkaller-02707-g614da38e2f7a #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/02/2024
=====================================================


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at [email protected].

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

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
If you attach or paste a git patch, syzbot will apply it before testing.

If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup