CVE-2024-58237

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

bpf: consider that tail calls invalidate packet pointers

Tail-called programs could execute any of the helpers that invalidate

packet pointers. Hence, conservatively assume that each tail call

invalidates packet pointers.

Making the change in bpf_helper_changes_pkt_data() automatically makes

use of check_cfg() logic that computes 'changes_pkt_data' effect for

global sub-programs, such that the following program could be

rejected:

int tail_call(struct __sk_buff *sk)

{

bpf_tail_call_static(sk, &jmp_table, 0);

return 0;

}

SEC("tc")

int not_safe(struct __sk_buff *sk)

{

int *p = (void *)(long)sk->data;

... make p valid ...

tail_call(sk);

*p = 42; /* this is unsafe */

...

}

The tc_bpf2bpf.c:subprog_tc() needs change: mark it as a function that

can invalidate packet pointers. Otherwise, it can't be freplaced with

tailcall_freplace.c:entry_freplace() that does a tail call.