[syzbot] [can?] KMSAN: kernel-infoleak in raw_recvmsg

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 71b1543c83d6 Merge tag '6.9-rc5-ksmbd-fixes' of git://git...
git tree: upstream
console+strace: https://syzkaller.appspot.com/x/log.txt?x=1784bdd7180000
kernel config: https://syzkaller.appspot.com/x/.config?x=776c05250f36d55c
dashboard link: https://syzkaller.appspot.com/bug?extid=5681e40d297b30f5b513
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=15b440d3180000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=14b00907180000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/14813ccfbcb3/disk-71b1543c.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/e7b88b42cf07/vmlinux-71b1543c.xz
kernel image: https://storage.googleapis.com/syzbot-assets/3a64a5abfbba/bzImage-71b1543c.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+5681e4...@syzkaller.appspotmail.com

=====================================================
BUG: KMSAN: kernel-infoleak in instrument_copy_to_user include/linux/instrumented.h:114 [inline]
BUG: KMSAN: kernel-infoleak in copy_to_user_iter lib/iov_iter.c:24 [inline]
BUG: KMSAN: kernel-infoleak in iterate_ubuf include/linux/iov_iter.h:29 [inline]
BUG: KMSAN: kernel-infoleak in iterate_and_advance2 include/linux/iov_iter.h:245 [inline]
BUG: KMSAN: kernel-infoleak in iterate_and_advance include/linux/iov_iter.h:271 [inline]
BUG: KMSAN: kernel-infoleak in _copy_to_iter+0x366/0x2520 lib/iov_iter.c:185
instrument_copy_to_user include/linux/instrumented.h:114 [inline]
copy_to_user_iter lib/iov_iter.c:24 [inline]
iterate_ubuf include/linux/iov_iter.h:29 [inline]
iterate_and_advance2 include/linux/iov_iter.h:245 [inline]
iterate_and_advance include/linux/iov_iter.h:271 [inline]
_copy_to_iter+0x366/0x2520 lib/iov_iter.c:185
copy_to_iter include/linux/uio.h:196 [inline]
memcpy_to_msg include/linux/skbuff.h:4113 [inline]
raw_recvmsg+0x2b8/0x9e0 net/can/raw.c:1008
sock_recvmsg_nosec net/socket.c:1046 [inline]
sock_recvmsg+0x2c4/0x340 net/socket.c:1068
____sys_recvmsg+0x18a/0x620 net/socket.c:2803
___sys_recvmsg+0x223/0x840 net/socket.c:2845
do_recvmmsg+0x4fc/0xfd0 net/socket.c:2939
__sys_recvmmsg net/socket.c:3018 [inline]
__do_sys_recvmmsg net/socket.c:3041 [inline]
__se_sys_recvmmsg net/socket.c:3034 [inline]
__x64_sys_recvmmsg+0x397/0x490 net/socket.c:3034
x64_sys_call+0xf6c/0x3b50 arch/x86/include/generated/asm/syscalls_64.h:300
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:3804 [inline]
slab_alloc_node mm/slub.c:3845 [inline]
kmem_cache_alloc_node+0x613/0xc50 mm/slub.c:3888
kmalloc_reserve+0x13d/0x4a0 net/core/skbuff.c:577
__alloc_skb+0x35b/0x7a0 net/core/skbuff.c:668
alloc_skb include/linux/skbuff.h:1313 [inline]
alloc_skb_with_frags+0xc8/0xbf0 net/core/skbuff.c:6504
sock_alloc_send_pskb+0xa81/0xbf0 net/core/sock.c:2795
sock_alloc_send_skb include/net/sock.h:1842 [inline]
j1939_sk_alloc_skb net/can/j1939/socket.c:878 [inline]
j1939_sk_send_loop net/can/j1939/socket.c:1142 [inline]
j1939_sk_sendmsg+0xc0a/0x2730 net/can/j1939/socket.c:1277
sock_sendmsg_nosec net/socket.c:730 [inline]
__sock_sendmsg+0x30f/0x380 net/socket.c:745
____sys_sendmsg+0x877/0xb60 net/socket.c:2584
___sys_sendmsg+0x28d/0x3c0 net/socket.c:2638
__sys_sendmsg net/socket.c:2667 [inline]
__do_sys_sendmsg net/socket.c:2676 [inline]
__se_sys_sendmsg net/socket.c:2674 [inline]
__x64_sys_sendmsg+0x307/0x4a0 net/socket.c:2674
x64_sys_call+0xc4b/0x3b50 arch/x86/include/generated/asm/syscalls_64.h:47
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

Bytes 12-15 of 16 are uninitialized
Memory access of size 16 starts at ffff888120969690
Data copied to user address 00000000200017c0

CPU: 1 PID: 5050 Comm: syz-executor198 Not tainted 6.9.0-rc5-syzkaller-00031-g71b1543c83d6 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/27/2024
=====================================================


---
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[Oliver Hartkopp]

Hello Oleksij,

can this probably be caused by a missing initialization of unused data
in j1939_sk_alloc_skb()?

Best regards,
Oliver