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

Affected Software

References

• https://git.kernel.org/stable/c/2b4c99f7d9a57ecd644eda9b1fb0a1072414959f
• https://git.kernel.org/stable/c/2e6ad51c709fa794e0ce26003c9c9cd944e3383a
• https://git.kernel.org/stable/c/3fa0f1e0e31b1b73cdf59d4c36c7242e6ef821be
• https://git.kernel.org/stable/c/618b15d09fed6126356101543451d49860db4388
• https://git.kernel.org/stable/c/78bc7f0ab99458221224d3ab97199c0f8e6861f1
• https://git.kernel.org/stable/c/ab2a55907823f0bca56b6d03ea05e4071ba8535f
• https://git.kernel.org/stable/c/bf70e0eab64c625da84d9fdf4e84466b79418920
• https://git.kernel.org/stable/c/c11dbc7705b3739974ac31a13f4ab81e61a5fb07