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.
Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20241210041100.1898468-8-eddyz87@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Add a test case to ensure that attaching a tail callee program with an
freplace program fails, and that updating an extended program to a
prog_array map is also prohibited.
This test is designed to prevent the potential infinite loop issue caused
by the combination of tail calls and freplace, ensuring the correct
behavior and stability of the system.
Additionally, fix the broken tailcalls/tailcall_freplace selftest
because an extension prog should not be tailcalled.
cd tools/testing/selftests/bpf; ./test_progs -t tailcalls
337/25 tailcalls/tailcall_freplace:OK
337/26 tailcalls/tailcall_bpf2bpf_freplace:OK
337 tailcalls:OK
Summary: 1/26 PASSED, 0 SKIPPED, 0 FAILED
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Leon Hwang <leon.hwang@linux.dev>
Link: https://lore.kernel.org/r/20241015150207.70264-3-leon.hwang@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Add a selftest to confirm the issue, which gets -EINVAL when update
attached freplace prog to prog_array map, has been fixed.
cd tools/testing/selftests/bpf; ./test_progs -t tailcalls
328/25 tailcalls/tailcall_freplace:OK
328 tailcalls:OK
Summary: 1/25 PASSED, 0 SKIPPED, 0 FAILED
Acked-by: Yonghong Song <yonghong.song@linux.dev>
Signed-off-by: Leon Hwang <leon.hwang@linux.dev>
Link: https://lore.kernel.org/r/20240728114612.48486-3-leon.hwang@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
