On Wed, Oct 27, 2021 at 11:35 PM Kumar Kartikeya Dwivedi
<memxor@xxxxxxxxx> wrote:
>
> Add a simple wrapper for passing an fd and getting a new one >= 3 if it
> is one of 0, 1, or 2. There are two primary reasons to make this change:
> First, libbpf relies on the assumption a certain BPF fd is never 0 (e.g.
> most recently noticed in [0]). Second, Alexei pointed out in [1] that
> some environments reset stdin, stdout, and stderr if they notice an
> invalid fd at these numbers. To protect against both these cases, switch
> all internal BPF syscall wrappers in libbpf to always return an fd >= 3.
> We only need to modify the syscall wrappers and not other code that
> assumes a valid fd by doing >= 0, to avoid pointless churn, and because
> it is still a valid assumption. The cost paid is two additional syscalls
> if fd is in range [0, 2].
>
> [0]: e31eec77e4ab ("bpf: selftests: Fix fd cleanup in get_branch_snapshot")
> [1]: https://lore.kernel.org/bpf/CAADnVQKVKY8o_3aU8Gzke443+uHa-eGoM0h7W4srChMXU1S4Bg@xxxxxxxxxxxxxx
>
> Acked-by: Song Liu <songliubraving@xxxxxx>
> Signed-off-by: Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx>
> ---
LGTM, thanks.
Acked-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
> tools/lib/bpf/bpf.c | 35 +++++++++++++++++++++------------
> tools/lib/bpf/libbpf_internal.h | 24 ++++++++++++++++++++++
> 2 files changed, 46 insertions(+), 13 deletions(-)
>
[...]
