can: bcm: bcm_tx_setup(): fix KMSAN uninit-value in vfs_write

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

can: bcm: bcm_tx_setup(): fix KMSAN uninit-value in vfs_write

Syzkaller reported the following issue:

=====================================================

BUG: KMSAN: uninit-value in aio_rw_done fs/aio.c:1520 [inline]

BUG: KMSAN: uninit-value in aio_write+0x899/0x950 fs/aio.c:1600

aio_rw_done fs/aio.c:1520 [inline]

aio_write+0x899/0x950 fs/aio.c:1600

io_submit_one+0x1d1c/0x3bf0 fs/aio.c:2019

__do_sys_io_submit fs/aio.c:2078 [inline]

__se_sys_io_submit+0x293/0x770 fs/aio.c:2048

__x64_sys_io_submit+0x92/0xd0 fs/aio.c:2048

do_syscall_x64 arch/x86/entry/common.c:50 [inline]

do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80

entry_SYSCALL_64_after_hwframe+0x63/0xcd

Uninit was created at:

slab_post_alloc_hook mm/slab.h:766 [inline]

slab_alloc_node mm/slub.c:3452 [inline]

__kmem_cache_alloc_node+0x71f/0xce0 mm/slub.c:3491

__do_kmalloc_node mm/slab_common.c:967 [inline]

__kmalloc+0x11d/0x3b0 mm/slab_common.c:981

kmalloc_array include/linux/slab.h:636 [inline]

bcm_tx_setup+0x80e/0x29d0 net/can/bcm.c:930

bcm_sendmsg+0x3a2/0xce0 net/can/bcm.c:1351

sock_sendmsg_nosec net/socket.c:714 [inline]

sock_sendmsg net/socket.c:734 [inline]

sock_write_iter+0x495/0x5e0 net/socket.c:1108

call_write_iter include/linux/fs.h:2189 [inline]

aio_write+0x63a/0x950 fs/aio.c:1600

io_submit_one+0x1d1c/0x3bf0 fs/aio.c:2019

__do_sys_io_submit fs/aio.c:2078 [inline]

__se_sys_io_submit+0x293/0x770 fs/aio.c:2048

__x64_sys_io_submit+0x92/0xd0 fs/aio.c:2048

do_syscall_x64 arch/x86/entry/common.c:50 [inline]

do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80

entry_SYSCALL_64_after_hwframe+0x63/0xcd

CPU: 1 PID: 5034 Comm: syz-executor350 Not tainted 6.2.0-rc6-syzkaller-80422-geda666ff2276 #0

Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/12/2023

=====================================================

We can follow the call chain and find that 'bcm_tx_setup' function

calls 'memcpy_from_msg' to copy some content to the newly allocated

frame of 'op->frames'. After that the 'len' field of copied structure

being compared with some constant value (64 or 8). However, if

'memcpy_from_msg' returns an error, we will compare some uninitialized

memory. This triggers 'uninit-value' issue.

This patch will add 'memcpy_from_msg' possible errors processing to

avoid uninit-value issue.

Tested via syzkaller