From: Kees Cook <keescook@chromium.org>
To: Andrii Nakryiko <andrii@kernel.org>
Cc: bpf@vger.kernel.org, ast@kernel.org, daniel@iogearbox.net,
kpsingh@kernel.org, paul@paul-moore.com,
linux-security-module@vger.kernel.org
Subject: Re: [PATCH bpf-next 1/8] bpf: move unprivileged checks into map_create() and bpf_prog_load()
Date: Wed, 12 Apr 2023 10:49:42 -0700 [thread overview]
Message-ID: <6436ef37.170a0220.d660b.33fe@mx.google.com> (raw)
In-Reply-To: <20230412043300.360803-2-andrii@kernel.org>
On Tue, Apr 11, 2023 at 09:32:53PM -0700, Andrii Nakryiko wrote:
> Make each bpf() syscall command a bit more self-contained, making it
> easier to further enhance it. We move sysctl_unprivileged_bpf_disabled
> handling down to map_create() and bpf_prog_load(), two special commands
> in this regard.
>
> Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
> ---
> kernel/bpf/syscall.c | 37 ++++++++++++++++++++++---------------
> 1 file changed, 22 insertions(+), 15 deletions(-)
>
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index 6d575505f89c..c1d268025985 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -1130,6 +1130,17 @@ static int map_create(union bpf_attr *attr)
> int f_flags;
> int err;
>
> + /* Intent here is for unprivileged_bpf_disabled to block key object
> + * creation commands for unprivileged users; other actions depend
> + * of fd availability and access to bpffs, so are dependent on
> + * object creation success. Capabilities are later verified for
> + * operations such as load and map create, so even with unprivileged
> + * BPF disabled, capability checks are still carried out for these
> + * and other operations.
> + */
> + if (!bpf_capable() && sysctl_unprivileged_bpf_disabled)
> + return -EPERM;
This appears to be a problem in the original code, but capability checks
should be last, so that audit doesn't see a capability as having been
used when it wasn't. i.e. if bpf_capable() passes, but
sysctl_unprivileged_bpf_disabled isn't true, it'll look like a
capability got used, and the flag gets set. Not a big deal at the end of
the day, but the preferred ordering should be:
if (sysctl_unprivileged_bpf_disabled && !bpf_capable())
...
> +
> err = CHECK_ATTR(BPF_MAP_CREATE);
> if (err)
> return -EINVAL;
> @@ -2512,6 +2523,17 @@ static int bpf_prog_load(union bpf_attr *attr, bpfptr_t uattr, u32 uattr_size)
> char license[128];
> bool is_gpl;
>
> + /* Intent here is for unprivileged_bpf_disabled to block key object
> + * creation commands for unprivileged users; other actions depend
> + * of fd availability and access to bpffs, so are dependent on
> + * object creation success. Capabilities are later verified for
> + * operations such as load and map create, so even with unprivileged
> + * BPF disabled, capability checks are still carried out for these
> + * and other operations.
> + */
> + if (!bpf_capable() && sysctl_unprivileged_bpf_disabled)
> + return -EPERM;
> +
> if (CHECK_ATTR(BPF_PROG_LOAD))
> return -EINVAL;
>
> @@ -5008,23 +5030,8 @@ static int bpf_prog_bind_map(union bpf_attr *attr)
> static int __sys_bpf(int cmd, bpfptr_t uattr, unsigned int size)
> {
> union bpf_attr attr;
> - bool capable;
> int err;
>
> - capable = bpf_capable() || !sysctl_unprivileged_bpf_disabled;
> -
> - /* Intent here is for unprivileged_bpf_disabled to block key object
> - * creation commands for unprivileged users; other actions depend
> - * of fd availability and access to bpffs, so are dependent on
> - * object creation success. Capabilities are later verified for
> - * operations such as load and map create, so even with unprivileged
> - * BPF disabled, capability checks are still carried out for these
> - * and other operations.
> - */
> - if (!capable &&
> - (cmd == BPF_MAP_CREATE || cmd == BPF_PROG_LOAD))
> - return -EPERM;
> -
> err = bpf_check_uarg_tail_zero(uattr, sizeof(attr), size);
> if (err)
> return err;
> --
> 2.34.1
>
--
Kees Cook
next prev parent reply other threads:[~2023-04-12 17:49 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-04-12 4:32 [PATCH bpf-next 0/8] New BPF map and BTF security LSM hooks Andrii Nakryiko
2023-04-12 4:32 ` [PATCH bpf-next 1/8] bpf: move unprivileged checks into map_create() and bpf_prog_load() Andrii Nakryiko
2023-04-12 17:49 ` Kees Cook [this message]
2023-04-13 0:22 ` Andrii Nakryiko
2023-04-12 4:32 ` [PATCH bpf-next 2/8] bpf: inline map creation logic in map_create() function Andrii Nakryiko
2023-04-12 17:53 ` Kees Cook
2023-04-13 0:22 ` Andrii Nakryiko
2023-04-12 4:32 ` [PATCH bpf-next 3/8] bpf: centralize permissions checks for all BPF map types Andrii Nakryiko
2023-04-12 18:01 ` Kees Cook
2023-04-13 0:23 ` Andrii Nakryiko
2023-04-12 4:32 ` [PATCH bpf-next 4/8] bpf, lsm: implement bpf_map_create_security LSM hook Andrii Nakryiko
2023-04-12 18:20 ` Kees Cook
2023-04-13 0:23 ` Andrii Nakryiko
2023-04-12 4:32 ` [PATCH bpf-next 5/8] selftests/bpf: validate new " Andrii Nakryiko
2023-04-12 18:23 ` Kees Cook
2023-04-13 0:23 ` Andrii Nakryiko
2023-04-12 4:32 ` [PATCH bpf-next 6/8] bpf: drop unnecessary bpf_capable() check in BPF_MAP_FREEZE command Andrii Nakryiko
2023-04-12 18:24 ` Kees Cook
2023-04-13 0:17 ` Andrii Nakryiko
2023-04-12 4:32 ` [PATCH bpf-next 7/8] bpf, lsm: implement bpf_btf_load_security LSM hook Andrii Nakryiko
2023-04-12 16:52 ` Paul Moore
2023-04-13 1:43 ` Andrii Nakryiko
2023-04-13 2:47 ` Paul Moore
2023-04-12 4:33 ` [PATCH bpf-next 8/8] selftests/bpf: enhance lsm_map_create test with BTF LSM control Andrii Nakryiko
2023-04-12 16:49 ` [PATCH bpf-next 0/8] New BPF map and BTF security LSM hooks Paul Moore
2023-04-12 17:47 ` Kees Cook
2023-04-12 18:06 ` Paul Moore
2023-04-12 18:28 ` Kees Cook
2023-04-12 19:06 ` Paul Moore
2023-04-13 1:43 ` Andrii Nakryiko
2023-04-13 2:56 ` Paul Moore
2023-04-13 5:16 ` Andrii Nakryiko
2023-04-13 15:11 ` Paul Moore
2023-04-17 23:29 ` Andrii Nakryiko
2023-04-18 0:47 ` Casey Schaufler
2023-04-21 0:00 ` Andrii Nakryiko
2023-04-18 14:21 ` Paul Moore
2023-04-21 0:00 ` Andrii Nakryiko
2023-04-21 18:57 ` Kees Cook
2023-04-13 16:54 ` Casey Schaufler
2023-04-17 23:31 ` Andrii Nakryiko
2023-04-13 19:03 ` Jonathan Corbet
2023-04-17 23:28 ` Andrii Nakryiko
2023-04-13 16:27 ` Casey Schaufler
2023-04-17 23:31 ` Andrii Nakryiko
2023-04-17 23:53 ` Casey Schaufler
2023-04-18 0:28 ` Andrii Nakryiko
2023-04-18 0:52 ` Casey Schaufler
2023-04-12 18:38 ` Casey Schaufler
2023-04-14 20:23 ` Dr. Greg
2023-04-17 23:31 ` Andrii Nakryiko
2023-04-19 10:53 ` Dr. Greg
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