Wind River Support Network

Description

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

bpf: Prevent tailcall infinite loop caused by freplace

There is a potential infinite loop issue that can occur when using a
combination of tail calls and freplace.

In an upcoming selftest, the attach target for entry_freplace of
tailcall_freplace.c is subprog_tc of tc_bpf2bpf.c, while the tail call in
entry_freplace leads to entry_tc. This results in an infinite loop:

entry_tc {-}> subprog_tc -> entry_freplace --tailcall{-}> entry_tc.

The problem arises because the tail_call_cnt in entry_freplace resets to
zero each time entry_freplace is executed, causing the tail call mechanism
to never terminate, eventually leading to a kernel panic.

To fix this issue, the solution is twofold:

1. Prevent updating a program extended by an freplace program to a
prog_array map.
2. Prevent extending a program that is already part of a prog_array map
with an freplace program.

This ensures that:
 * If a program or its subprogram has been extended by an freplace program,
it can no longer be updated to a prog_array map.
 * If a program has been added to a prog_array map, neither it nor its
subprograms can be extended by an freplace program.

Moreover, an extension program should not be tailcalled. As such, return
-EINVAL if the program has a type of BPF_PROG_TYPE_EXT when adding it to a
prog_array map.

Additionally, fix a minor code style issue by replacing eight spaces with a
tab for proper formatting.

 

========Wind River Notice========

This fix of CVE has big changes. so backport the fix to current kernel might cause more issues.

There is a simple way to mitigate it, see:

[https://access.redhat.com/security/cve/cve-2024-47794]

 

Mitigating steps(Verified on qemu-x86-64):

1. Checking unprivileged_bpf_disabled:

cat /proc/sys/kernel/unprivileged_bpf_disabled

2. The setting of 1 would mean that unprivileged users can not use eBPF, mitigating the flaw:

echo 1 > /proc/sys/kernel/unprivileged_bpf_disabled

CVEs

• CVE-2024-47794