CVE-2024-42076: net: can: j1939: Initialize unused data in j1939_send_one()

In the Linux kernel, the following vulnerability has been resolved:

net: can: j1939: Initialize unused data in j1939sendone()

syzbot reported kernel-infoleak in rawrecvmsg() [1]. j1939sendone() creates full frame including unused data, but it doesn't initialize it. This causes the kernel-infoleak issue. Fix this by initializing unused data.

[1] BUG: KMSAN: kernel-infoleak in instrumentcopytouser include/linux/instrumented.h:114 [inline] BUG: KMSAN: kernel-infoleak in copytouseriter lib/ioviter.c:24 [inline] BUG: KMSAN: kernel-infoleak in iterateubuf include/linux/ioviter.h:29 [inline] BUG: KMSAN: kernel-infoleak in iterateandadvance2 include/linux/ioviter.h:245 [inline] BUG: KMSAN: kernel-infoleak in iterateandadvance include/linux/ioviter.h:271 [inline] BUG: KMSAN: kernel-infoleak in copytoiter+0x366/0x2520 lib/ioviter.c:185 instrumentcopytouser include/linux/instrumented.h:114 [inline] copytouseriter lib/ioviter.c:24 [inline] iterateubuf include/linux/ioviter.h:29 [inline] iterateandadvance2 include/linux/ioviter.h:245 [inline] iterateandadvance include/linux/ioviter.h:271 [inline] copytoiter+0x366/0x2520 lib/ioviter.c:185 copytoiter include/linux/uio.h:196 [inline] memcpytomsg include/linux/skbuff.h:4113 [inline] rawrecvmsg+0x2b8/0x9e0 net/can/raw.c:1008 sockrecvmsgnosec net/socket.c:1046 [inline] sockrecvmsg+0x2c4/0x340 net/socket.c:1068 sysrecvmsg+0x18a/0x620 net/socket.c:2803 sysrecvmsg+0x223/0x840 net/socket.c:2845 dorecvmmsg+0x4fc/0xfd0 net/socket.c:2939 sysrecvmmsg net/socket.c:3018 [inline] dosysrecvmmsg net/socket.c:3041 [inline] sesysrecvmmsg net/socket.c:3034 [inline] x64sysrecvmmsg+0x397/0x490 net/socket.c:3034 x64syscall+0xf6c/0x3b50 arch/x86/include/generated/asm/syscalls64.h:300 dosyscallx64 arch/x86/entry/common.c:52 [inline] dosyscall64+0xcf/0x1e0 arch/x86/entry/common.c:83 entrySYSCALL64afterhwframe+0x77/0x7f

Uninit was created at: slabpostallochook mm/slub.c:3804 [inline] slaballocnode mm/slub.c:3845 [inline] kmemcacheallocnode+0x613/0xc50 mm/slub.c:3888 kmallocreserve+0x13d/0x4a0 net/core/skbuff.c:577 allocskb+0x35b/0x7a0 net/core/skbuff.c:668 allocskb include/linux/skbuff.h:1313 [inline] allocskbwithfrags+0xc8/0xbf0 net/core/skbuff.c:6504 sockallocsendpskb+0xa81/0xbf0 net/core/sock.c:2795 sockallocsendskb include/net/sock.h:1842 [inline] j1939skallocskb net/can/j1939/socket.c:878 [inline] j1939sksendloop net/can/j1939/socket.c:1142 [inline] j1939sksendmsg+0xc0a/0x2730 net/can/j1939/socket.c:1277 socksendmsgnosec net/socket.c:730 [inline] socksendmsg+0x30f/0x380 net/socket.c:745 syssendmsg+0x877/0xb60 net/socket.c:2584 syssendmsg+0x28d/0x3c0 net/socket.c:2638 syssendmsg net/socket.c:2667 [inline] dosyssendmsg net/socket.c:2676 [inline] sesyssendmsg net/socket.c:2674 [inline] x64syssendmsg+0x307/0x4a0 net/socket.c:2674 x64syscall+0xc4b/0x3b50 arch/x86/include/generated/asm/syscalls64.h:47 dosyscallx64 arch/x86/entry/common.c:52 [inline] dosyscall64+0xcf/0x1e0 arch/x86/entry/common.c:83 entrySYSCALL64afterhwframe+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