Subject: CVE-2024-38538: net: bridge: xmit: make sure we have at least eth header len bytes

From: Greg Kroah-Hartman <[email-masked]>

Description
===========

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

The Linux kernel CVE team has assigned CVE-2024-38538 to this issue.

Affected and fixed versions
===========================

	Issue introduced in 2.6.12 with commit 1da177e4c3f4 and fixed in 6.1.93 with commit 28126b83f86a
	Issue introduced in 2.6.12 with commit 1da177e4c3f4 and fixed in 6.6.33 with commit 1abb37114790
	Issue introduced in 2.6.12 with commit 1da177e4c3f4 and fixed in 6.8.12 with commit f482fd4ce919
	Issue introduced in 2.6.12 with commit 1da177e4c3f4 and fixed in 6.9.3 with commit 5b5d669f5698
	Issue introduced in 2.6.12 with commit 1da177e4c3f4 and fixed in 6.10 with commit 8bd67ebb50c0

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2024-38538
will be updated if fixes are backported, please check that for the most
up to date information about this issue.

Affected files
==============

The file(s) affected by this issue are:
	net/bridge/br_device.c

Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/28126b83f86ab9cc7936029c2dff845d3dcedba2
	https://git.kernel.org/stable/c/1abb371147905ba250b4cc0230c4be7e90bea4d5
	https://git.kernel.org/stable/c/f482fd4ce919836a49012b2d31b00fc36e2488f2
	https://git.kernel.org/stable/c/5b5d669f569807c7ab07546e73c0741845a2547a
	https://git.kernel.org/stable/c/8bd67ebb50c0145fd2ca8681ab65eb7e8cde1afc