[syzbot] [ppp?] KMSAN: uninit-value in ppp_sync_send (2)

Hello,

syzbot found the following issue on:

HEAD commit:    9946eaf552b1 Merge tag 'hardening-v6.14-rc2' of git://git...
git tree:       upstream
console+strace: https://syzkaller.appspot.com/x/log.txt?x=131dabdf980000
kernel config:  https://syzkaller.appspot.com/x/.config?x=f20bce78db15972a
dashboard link: https://syzkaller.appspot.com/bug?extid=29fc8991b0ecb186cf40
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=17b142a4580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=14167df8580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/955ec208b383/disk-9946eaf5.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/ccb7613686d1/vmlinux-9946eaf5.xz
kernel image: https://storage.googleapis.com/syzbot-assets/10b92522362a/bzImage-9946eaf5.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_sync_txmunge drivers/net/ppp/ppp_synctty.c:516 [inline]
BUG: KMSAN: uninit-value in ppp_sync_send+0x21c/0xb00 drivers/net/ppp/ppp_synctty.c:568
 ppp_sync_txmunge drivers/net/ppp/ppp_synctty.c:516 [inline]
 ppp_sync_send+0x21c/0xb00 drivers/net/ppp/ppp_synctty.c:568
 ppp_channel_bridge_input drivers/net/ppp/ppp_generic.c:2280 [inline]
 ppp_input+0x1f1/0xe60 drivers/net/ppp/ppp_generic.c:2304
 pppoe_rcv_core+0x1d3/0x720 drivers/net/ppp/pppoe.c:379
 sk_backlog_rcv+0x13b/0x420 include/net/sock.h:1122
 __release_sock+0x1da/0x330 net/core/sock.c:3106
 release_sock+0x6b/0x250 net/core/sock.c:3660
 pppoe_sendmsg+0xb35/0xc50 drivers/net/ppp/pppoe.c:903
 sock_sendmsg_nosec net/socket.c:718 [inline]
 __sock_sendmsg+0x30f/0x380 net/socket.c:733
 ____sys_sendmsg+0x903/0xb60 net/socket.c:2573
 ___sys_sendmsg+0x28d/0x3c0 net/socket.c:2627
 __sys_sendmmsg+0x2ff/0x880 net/socket.c:2716
 __do_sys_sendmmsg net/socket.c:2743 [inline]
 __se_sys_sendmmsg net/socket.c:2740 [inline]
 __x64_sys_sendmmsg+0xbc/0x120 net/socket.c:2740
 x64_sys_call+0x33c2/0x3c30 arch/x86/include/generated/asm/syscalls_64.h:308
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xcd/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:4121 [inline]
 slab_alloc_node mm/slub.c:4164 [inline]
 kmem_cache_alloc_node_noprof+0x907/0xe00 mm/slub.c:4216
 kmalloc_reserve+0x13d/0x4a0 net/core/skbuff.c:587
 __alloc_skb+0x363/0x7b0 net/core/skbuff.c:678
 alloc_skb include/linux/skbuff.h:1331 [inline]
 sock_wmalloc+0xfe/0x1a0 net/core/sock.c:2746
 pppoe_sendmsg+0x385/0xc50 drivers/net/ppp/pppoe.c:867
 sock_sendmsg_nosec net/socket.c:718 [inline]
 __sock_sendmsg+0x30f/0x380 net/socket.c:733
 ____sys_sendmsg+0x903/0xb60 net/socket.c:2573
 ___sys_sendmsg+0x28d/0x3c0 net/socket.c:2627
 __sys_sendmmsg+0x2ff/0x880 net/socket.c:2716
 __do_sys_sendmmsg net/socket.c:2743 [inline]
 __se_sys_sendmmsg net/socket.c:2740 [inline]
 __x64_sys_sendmmsg+0xbc/0x120 net/socket.c:2740
 x64_sys_call+0x33c2/0x3c30 arch/x86/include/generated/asm/syscalls_64.h:308
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xcd/0x1e0 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

CPU: 1 UID: 0 PID: 5806 Comm: syz-executor201 Not tainted 6.14.0-rc1-syzkaller-00235-g9946eaf552b1 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 12/27/2024
=====================================================


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