CVE-2024-47794

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.