bpf: Fix stack-out-of-bounds write in devmap

Overview

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

bpf: Fix stack-out-of-bounds write in devmap

get_upper_ifindexes() iterates over all upper devices and writes their indices into an array without checking bounds.

Also the callers assume that the max number of upper devices is MAX_NEST_DEV and allocate excluded_devices[1+MAX_NEST_DEV] on the stack, but that assumption is not correct and the number of upper devices could be larger than MAX_NEST_DEV (e.g., many macvlans), causing a stack-out-of-bounds write.

Add a max parameter to get_upper_ifindexes() to avoid the issue. When there are too many upper devices, return -EOVERFLOW and abort the redirect.

To reproduce, create more than MAX_NEST_DEV(8) macvlans on a device with an XDP program attached using BPF_F_BROADCAST | BPF_F_EXCLUDE_INGRESS. Then send a packet to the device to trigger the XDP redirect path.

Affected

• Linux >= aeea1b86f9363f3feabb496534d886f082a89f21 < 88df604f0d16a692867582350ce3f2fcd22243f1
• Linux >= aeea1b86f9363f3feabb496534d886f082a89f21 < 5000e40acc8d0c36ab709662e32120986ac22e7e
• Linux >= aeea1b86f9363f3feabb496534d886f082a89f21 < 8a95fb9df1105b1618872c2846a6c01e3ba20b45
• Linux >= aeea1b86f9363f3feabb496534d886f082a89f21 < d2c31d8e03d05edc16656e5ffe187f0d1da763d7
• Linux >= aeea1b86f9363f3feabb496534d886f082a89f21 < 75d474702b2ba8b6bcb26eb3004dbc5e95ffd5d2
• Linux >= aeea1b86f9363f3feabb496534d886f082a89f21 < ca831567908fd3f73cf97d8a6c09a5054697a182
• Linux >= aeea1b86f9363f3feabb496534d886f082a89f21 < b7bf516c3ecd9a2aae2dc2635178ab87b734fef1
• Linux 5.15

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.