CVE-2024-38538

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

net: bridge: xmit: make sure we have at least eth header len bytes

syzbot triggered an uninit value[1] error in bridge device's xmit path

by sending a short (less than ETH_HLEN bytes) skb. To fix it check if

we can actually pull that amount instead of assuming.

Tested with dropwatch:

drop at: br_dev_xmit+0xb93/0x12d0 [bridge] (0xffffffffc06739b3)

origin: software

timestamp: Mon May 13 11:31:53 2024 778214037 nsec

protocol: 0x88a8

length: 2

original length: 2

drop reason: PKT_TOO_SMALL

[1]

BUG: KMSAN: uninit-value in br_dev_xmit+0x61d/0x1cb0 net/bridge/br_device.c:65

br_dev_xmit+0x61d/0x1cb0 net/bridge/br_device.c:65

__netdev_start_xmit include/linux/netdevice.h:4903 [inline]

netdev_start_xmit include/linux/netdevice.h:4917 [inline]

xmit_one net/core/dev.c:3531 [inline]

dev_hard_start_xmit+0x247/0xa20 net/core/dev.c:3547

__dev_queue_xmit+0x34db/0x5350 net/core/dev.c:4341

dev_queue_xmit include/linux/netdevice.h:3091 [inline]

__bpf_tx_skb net/core/filter.c:2136 [inline]

__bpf_redirect_common net/core/filter.c:2180 [inline]

__bpf_redirect+0x14a6/0x1620 net/core/filter.c:2187

____bpf_clone_redirect net/core/filter.c:2460 [inline]

bpf_clone_redirect+0x328/0x470 net/core/filter.c:2432

___bpf_prog_run+0x13fe/0xe0f0 kernel/bpf/core.c:1997

__bpf_prog_run512+0xb5/0xe0 kernel/bpf/core.c:2238

bpf_dispatcher_nop_func include/linux/bpf.h:1234 [inline]

__bpf_prog_run include/linux/filter.h:657 [inline]

bpf_prog_run include/linux/filter.h:664 [inline]

bpf_test_run+0x499/0xc30 net/bpf/test_run.c:425

bpf_prog_test_run_skb+0x14ea/0x1f20 net/bpf/test_run.c:1058

bpf_prog_test_run+0x6b7/0xad0 kernel/bpf/syscall.c:4269

__sys_bpf+0x6aa/0xd90 kernel/bpf/syscall.c:5678

__do_sys_bpf kernel/bpf/syscall.c:5767 [inline]

__se_sys_bpf kernel/bpf/syscall.c:5765 [inline]

__x64_sys_bpf+0xa0/0xe0 kernel/bpf/syscall.c:5765

x64_sys_call+0x96b/0x3b50 arch/x86/include/generated/asm/syscalls_64.h:322

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