[PATCH bpf v2 1/2] bpf: enforce that struct_ops programs be GPL-only

[PATCH bpf v2 1/2] bpf: enforce that struct_ops programs be GPL-only

[Toke Høiland-Jørgensen]

With the introduction of the struct_ops program type, it became possible to
implement kernel functionality in BPF, making it viable to use BPF in place
of a regular kernel module for these particular operations.

Thus far, the only user of this mechanism is for implementing TCP
congestion control algorithms. These are clearly marked as GPL-only when
implemented as modules (as seen by the use of EXPORT_SYMBOL_GPL for
tcp_register_congestion_control()), so it seems like an oversight that this
was not carried over to BPF implementations. Since this is the only user
of the struct_ops mechanism, just enforcing GPL-only for the struct_ops
program type seems like the simplest way to fix this.

v2: Move check to the top of check_struct_ops_btf_id().

Fixes: 0baf26b0fcd7 ("bpf: tcp: Support tcp_congestion_ops in bpf")
Acked-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
---
 kernel/bpf/verifier.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 44e4ec1640f1..3a738724a380 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -12158,6 +12158,11 @@ static int check_struct_ops_btf_id(struct bpf_verifier_env *env)
 	u32 btf_id, member_idx;
 	const char *mname;
 
+	if (!prog->gpl_compatible) {
+		verbose(env, "struct ops programs must have a GPL compatible license\n");
+		return -EINVAL;
+	}
+
 	btf_id = prog->aux->attach_btf_id;
 	st_ops = bpf_struct_ops_find(btf_id);
 	if (!st_ops) {
-- 
2.31.0

[PATCH bpf v2 2/2] bpf/selftests: test that kernel rejects a TCP CC with an invalid license

[Toke Høiland-Jørgensen]

This adds a selftest to check that the verifier rejects a TCP CC struct_ops
with a non-GPL license.

v2:
- Use a minimal struct_ops BPF program instead of rewriting bpf_dctcp's
  license in memory.
- Check for the verifier reject message instead of just the return code.

Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
---
 .../selftests/bpf/prog_tests/bpf_tcp_ca.c     | 44 +++++++++++++++++++
 .../selftests/bpf/progs/bpf_nogpltcp.c        | 19 ++++++++
 2 files changed, 63 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/progs/bpf_nogpltcp.c

diff --git a/tools/testing/selftests/bpf/prog_tests/bpf_tcp_ca.c b/tools/testing/selftests/bpf/prog_tests/bpf_tcp_ca.c
index 37c5494a0381..a09c716528e1 100644
--- a/tools/testing/selftests/bpf/prog_tests/bpf_tcp_ca.c
+++ b/tools/testing/selftests/bpf/prog_tests/bpf_tcp_ca.c
@@ -6,6 +6,7 @@
 #include <test_progs.h>
 #include "bpf_dctcp.skel.h"
 #include "bpf_cubic.skel.h"
+#include "bpf_nogpltcp.skel.h"
 
 #define min(a, b) ((a) < (b) ? (a) : (b))
 
@@ -227,10 +228,53 @@ static void test_dctcp(void)
 	bpf_dctcp__destroy(dctcp_skel);
 }
 
+static char *err_str = NULL;
+static bool found = false;
+
+static int libbpf_debug_print(enum libbpf_print_level level,
+			      const char *format, va_list args)
+{
+	char *log_buf;
+
+	if (level != LIBBPF_WARN ||
+	    strcmp(format, "libbpf: \n%s\n")) {
+		vprintf(format, args);
+		return 0;
+	}
+
+	log_buf = va_arg(args, char *);
+	if (!log_buf)
+		goto out;
+	if (err_str && strstr(log_buf, err_str) != NULL)
+		found = true;
+out:
+	printf(format, log_buf);
+	return 0;
+}
+
+static void test_invalid_license(void)
+{
+	libbpf_print_fn_t old_print_fn = NULL;
+	struct bpf_nogpltcp *skel;
+
+	err_str = "struct ops programs must have a GPL compatible license";
+	old_print_fn = libbpf_set_print(libbpf_debug_print);
+
+	skel = bpf_nogpltcp__open_and_load();
+	if (CHECK(skel, "bpf_nogplgtcp__open_and_load()", "didn't fail\n"))
+		bpf_nogpltcp__destroy(skel);
+
+	CHECK(!found, "errmsg check", "expected string '%s'", err_str);
+
+	libbpf_set_print(old_print_fn);
+}
+
 void test_bpf_tcp_ca(void)
 {
 	if (test__start_subtest("dctcp"))
 		test_dctcp();
 	if (test__start_subtest("cubic"))
 		test_cubic();
+	if (test__start_subtest("invalid_license"))
+		test_invalid_license();
 }
diff --git a/tools/testing/selftests/bpf/progs/bpf_nogpltcp.c b/tools/testing/selftests/bpf/progs/bpf_nogpltcp.c
new file mode 100644
index 000000000000..2ecd833dcd41
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/bpf_nogpltcp.c
@@ -0,0 +1,19 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/bpf.h>
+#include <linux/types.h>
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+#include "bpf_tcp_helpers.h"
+
+char _license[] SEC("license") = "X";
+
+void BPF_STRUCT_OPS(nogpltcp_init, struct sock *sk)
+{
+}
+
+SEC(".struct_ops")
+struct tcp_congestion_ops bpf_nogpltcp = {
+	.init           = (void *)nogpltcp_init,
+	.name           = "bpf_nogpltcp",
+};
-- 
2.31.0

Re: [PATCH bpf v2 2/2] bpf/selftests: test that kernel rejects a TCP CC with an invalid license

[Martin KaFai Lau]

On Thu, Mar 25, 2021 at 10:11:22PM +0100, Toke Høiland-Jørgensen wrote:
> This adds a selftest to check that the verifier rejects a TCP CC struct_ops
> with a non-GPL license.
> 
> v2:
> - Use a minimal struct_ops BPF program instead of rewriting bpf_dctcp's
>   license in memory.
> - Check for the verifier reject message instead of just the return code.
> 
> Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
> ---
>  .../selftests/bpf/prog_tests/bpf_tcp_ca.c     | 44 +++++++++++++++++++
>  .../selftests/bpf/progs/bpf_nogpltcp.c        | 19 ++++++++
>  2 files changed, 63 insertions(+)
>  create mode 100644 tools/testing/selftests/bpf/progs/bpf_nogpltcp.c
> 
> diff --git a/tools/testing/selftests/bpf/prog_tests/bpf_tcp_ca.c b/tools/testing/selftests/bpf/prog_tests/bpf_tcp_ca.c
> index 37c5494a0381..a09c716528e1 100644
> --- a/tools/testing/selftests/bpf/prog_tests/bpf_tcp_ca.c
> +++ b/tools/testing/selftests/bpf/prog_tests/bpf_tcp_ca.c
> @@ -6,6 +6,7 @@
>  #include <test_progs.h>
>  #include "bpf_dctcp.skel.h"
>  #include "bpf_cubic.skel.h"
> +#include "bpf_nogpltcp.skel.h"
>  
>  #define min(a, b) ((a) < (b) ? (a) : (b))
>  
> @@ -227,10 +228,53 @@ static void test_dctcp(void)
>  	bpf_dctcp__destroy(dctcp_skel);
>  }
>  
> +static char *err_str = NULL;
> +static bool found = false;
Nit. These two inits are not needed.

> +
> +static int libbpf_debug_print(enum libbpf_print_level level,
> +			      const char *format, va_list args)
> +{
> +	char *log_buf;
> +
> +	if (level != LIBBPF_WARN ||
> +	    strcmp(format, "libbpf: \n%s\n")) {
> +		vprintf(format, args);
> +		return 0;
> +	}
> +
> +	log_buf = va_arg(args, char *);
> +	if (!log_buf)
> +		goto out;
> +	if (err_str && strstr(log_buf, err_str) != NULL)
> +		found = true;
> +out:
> +	printf(format, log_buf);
> +	return 0;
> +}
> +
> +static void test_invalid_license(void)
> +{
> +	libbpf_print_fn_t old_print_fn = NULL;
Nit. Same here.  Not need to init NULL.

Others lgtm.

Acked-by: Martin KaFai Lau <kafai@fb.com>

> +	struct bpf_nogpltcp *skel;
> +
> +	err_str = "struct ops programs must have a GPL compatible license";
> +	old_print_fn = libbpf_set_print(libbpf_debug_print);
> +
> +	skel = bpf_nogpltcp__open_and_load();
> +	if (CHECK(skel, "bpf_nogplgtcp__open_and_load()", "didn't fail\n"))
> +		bpf_nogpltcp__destroy(skel);
> +
> +	CHECK(!found, "errmsg check", "expected string '%s'", err_str);
> +
> +	libbpf_set_print(old_print_fn);
> +}

Re: [PATCH bpf v2 2/2] bpf/selftests: test that kernel rejects a TCP CC with an invalid license

[Andrii Nakryiko]

On Thu, Mar 25, 2021 at 2:11 PM Toke Høiland-Jørgensen <toke@redhat.com> wrote:
>
> This adds a selftest to check that the verifier rejects a TCP CC struct_ops
> with a non-GPL license.
>
> v2:
> - Use a minimal struct_ops BPF program instead of rewriting bpf_dctcp's
>   license in memory.
> - Check for the verifier reject message instead of just the return code.
>
> Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
> ---
>  .../selftests/bpf/prog_tests/bpf_tcp_ca.c     | 44 +++++++++++++++++++
>  .../selftests/bpf/progs/bpf_nogpltcp.c        | 19 ++++++++
>  2 files changed, 63 insertions(+)
>  create mode 100644 tools/testing/selftests/bpf/progs/bpf_nogpltcp.c
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/bpf_tcp_ca.c b/tools/testing/selftests/bpf/prog_tests/bpf_tcp_ca.c
> index 37c5494a0381..a09c716528e1 100644
> --- a/tools/testing/selftests/bpf/prog_tests/bpf_tcp_ca.c
> +++ b/tools/testing/selftests/bpf/prog_tests/bpf_tcp_ca.c
> @@ -6,6 +6,7 @@
>  #include <test_progs.h>
>  #include "bpf_dctcp.skel.h"
>  #include "bpf_cubic.skel.h"
> +#include "bpf_nogpltcp.skel.h"

total nit, but my eyes can't read "nogpltcp"... wouldn't
"bpf_tcp_nogpl" be a bit easier?

>
>  #define min(a, b) ((a) < (b) ? (a) : (b))
>
> @@ -227,10 +228,53 @@ static void test_dctcp(void)
>         bpf_dctcp__destroy(dctcp_skel);
>  }
>
> +static char *err_str = NULL;
> +static bool found = false;
> +
> +static int libbpf_debug_print(enum libbpf_print_level level,
> +                             const char *format, va_list args)
> +{
> +       char *log_buf;
> +
> +       if (level != LIBBPF_WARN ||
> +           strcmp(format, "libbpf: \n%s\n")) {
> +               vprintf(format, args);
> +               return 0;
> +       }
> +
> +       log_buf = va_arg(args, char *);
> +       if (!log_buf)
> +               goto out;
> +       if (err_str && strstr(log_buf, err_str) != NULL)
> +               found = true;
> +out:
> +       printf(format, log_buf);
> +       return 0;
> +}
> +
> +static void test_invalid_license(void)
> +{
> +       libbpf_print_fn_t old_print_fn = NULL;
> +       struct bpf_nogpltcp *skel;
> +
> +       err_str = "struct ops programs must have a GPL compatible license";
> +       old_print_fn = libbpf_set_print(libbpf_debug_print);
> +
> +       skel = bpf_nogpltcp__open_and_load();
> +       if (CHECK(skel, "bpf_nogplgtcp__open_and_load()", "didn't fail\n"))

ASSERT_OK_PTR()

> +               bpf_nogpltcp__destroy(skel);

you should destroy unconditionally

> +
> +       CHECK(!found, "errmsg check", "expected string '%s'", err_str);

ASSERT_EQ(found, true, "expected_err_msg");

I can never be sure which way CHECK() is checking

> +
> +       libbpf_set_print(old_print_fn);
> +}
> +
>  void test_bpf_tcp_ca(void)
>  {
>         if (test__start_subtest("dctcp"))
>                 test_dctcp();
>         if (test__start_subtest("cubic"))
>                 test_cubic();
> +       if (test__start_subtest("invalid_license"))
> +               test_invalid_license();
>  }
> diff --git a/tools/testing/selftests/bpf/progs/bpf_nogpltcp.c b/tools/testing/selftests/bpf/progs/bpf_nogpltcp.c
> new file mode 100644
> index 000000000000..2ecd833dcd41
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/bpf_nogpltcp.c
> @@ -0,0 +1,19 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +#include <linux/bpf.h>
> +#include <linux/types.h>
> +#include <bpf/bpf_helpers.h>
> +#include <bpf/bpf_tracing.h>
> +#include "bpf_tcp_helpers.h"
> +
> +char _license[] SEC("license") = "X";
> +
> +void BPF_STRUCT_OPS(nogpltcp_init, struct sock *sk)
> +{
> +}
> +
> +SEC(".struct_ops")
> +struct tcp_congestion_ops bpf_nogpltcp = {
> +       .init           = (void *)nogpltcp_init,
> +       .name           = "bpf_nogpltcp",
> +};
> --
> 2.31.0
>

Re: [PATCH bpf v2 2/2] bpf/selftests: test that kernel rejects a TCP CC with an invalid license

[Toke Høiland-Jørgensen]

Andrii Nakryiko <andrii.nakryiko@gmail.com> writes:

> On Thu, Mar 25, 2021 at 2:11 PM Toke Høiland-Jørgensen <toke@redhat.com> wrote:
>>
>> This adds a selftest to check that the verifier rejects a TCP CC struct_ops
>> with a non-GPL license.
>>
>> v2:
>> - Use a minimal struct_ops BPF program instead of rewriting bpf_dctcp's
>>   license in memory.
>> - Check for the verifier reject message instead of just the return code.
>>
>> Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
>> ---
>>  .../selftests/bpf/prog_tests/bpf_tcp_ca.c     | 44 +++++++++++++++++++
>>  .../selftests/bpf/progs/bpf_nogpltcp.c        | 19 ++++++++
>>  2 files changed, 63 insertions(+)
>>  create mode 100644 tools/testing/selftests/bpf/progs/bpf_nogpltcp.c
>>
>> diff --git a/tools/testing/selftests/bpf/prog_tests/bpf_tcp_ca.c b/tools/testing/selftests/bpf/prog_tests/bpf_tcp_ca.c
>> index 37c5494a0381..a09c716528e1 100644
>> --- a/tools/testing/selftests/bpf/prog_tests/bpf_tcp_ca.c
>> +++ b/tools/testing/selftests/bpf/prog_tests/bpf_tcp_ca.c
>> @@ -6,6 +6,7 @@
>>  #include <test_progs.h>
>>  #include "bpf_dctcp.skel.h"
>>  #include "bpf_cubic.skel.h"
>> +#include "bpf_nogpltcp.skel.h"
>
> total nit, but my eyes can't read "nogpltcp"... wouldn't
> "bpf_tcp_nogpl" be a bit easier?

Haha, yeah, good point - my eyes also just lump it into a blob...

>>
>>  #define min(a, b) ((a) < (b) ? (a) : (b))
>>
>> @@ -227,10 +228,53 @@ static void test_dctcp(void)
>>         bpf_dctcp__destroy(dctcp_skel);
>>  }
>>
>> +static char *err_str = NULL;
>> +static bool found = false;
>> +
>> +static int libbpf_debug_print(enum libbpf_print_level level,
>> +                             const char *format, va_list args)
>> +{
>> +       char *log_buf;
>> +
>> +       if (level != LIBBPF_WARN ||
>> +           strcmp(format, "libbpf: \n%s\n")) {
>> +               vprintf(format, args);
>> +               return 0;
>> +       }
>> +
>> +       log_buf = va_arg(args, char *);
>> +       if (!log_buf)
>> +               goto out;
>> +       if (err_str && strstr(log_buf, err_str) != NULL)
>> +               found = true;
>> +out:
>> +       printf(format, log_buf);
>> +       return 0;
>> +}
>> +
>> +static void test_invalid_license(void)
>> +{
>> +       libbpf_print_fn_t old_print_fn = NULL;
>> +       struct bpf_nogpltcp *skel;
>> +
>> +       err_str = "struct ops programs must have a GPL compatible license";
>> +       old_print_fn = libbpf_set_print(libbpf_debug_print);
>> +
>> +       skel = bpf_nogpltcp__open_and_load();
>> +       if (CHECK(skel, "bpf_nogplgtcp__open_and_load()", "didn't fail\n"))
>
> ASSERT_OK_PTR()
>
>> +               bpf_nogpltcp__destroy(skel);
>
> you should destroy unconditionally
>
>> +
>> +       CHECK(!found, "errmsg check", "expected string '%s'", err_str);
>
> ASSERT_EQ(found, true, "expected_err_msg");
>
> I can never be sure which way CHECK() is checking

Ah, thanks! I always get confused about CHECK() as well! Maybe it should
be renamed to ASSERT()? But that would require flipping all the if()
statements around them as well :/

-Toke

Re: [PATCH bpf v2 2/2] bpf/selftests: test that kernel rejects a TCP CC with an invalid license

[Andrii Nakryiko]

-- Andrii

On Fri, Mar 26, 2021 at 2:43 AM Toke Høiland-Jørgensen <toke@redhat.com> wrote:
>
> Andrii Nakryiko <andrii.nakryiko@gmail.com> writes:
>
> > On Thu, Mar 25, 2021 at 2:11 PM Toke Høiland-Jørgensen <toke@redhat.com> wrote:
> >>
> >> This adds a selftest to check that the verifier rejects a TCP CC struct_ops
> >> with a non-GPL license.
> >>
> >> v2:
> >> - Use a minimal struct_ops BPF program instead of rewriting bpf_dctcp's
> >>   license in memory.
> >> - Check for the verifier reject message instead of just the return code.
> >>
> >> Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
> >> ---
> >>  .../selftests/bpf/prog_tests/bpf_tcp_ca.c     | 44 +++++++++++++++++++
> >>  .../selftests/bpf/progs/bpf_nogpltcp.c        | 19 ++++++++
> >>  2 files changed, 63 insertions(+)
> >>  create mode 100644 tools/testing/selftests/bpf/progs/bpf_nogpltcp.c
> >>
> >> diff --git a/tools/testing/selftests/bpf/prog_tests/bpf_tcp_ca.c b/tools/testing/selftests/bpf/prog_tests/bpf_tcp_ca.c
> >> index 37c5494a0381..a09c716528e1 100644
> >> --- a/tools/testing/selftests/bpf/prog_tests/bpf_tcp_ca.c
> >> +++ b/tools/testing/selftests/bpf/prog_tests/bpf_tcp_ca.c
> >> @@ -6,6 +6,7 @@
> >>  #include <test_progs.h>
> >>  #include "bpf_dctcp.skel.h"
> >>  #include "bpf_cubic.skel.h"
> >> +#include "bpf_nogpltcp.skel.h"
> >
> > total nit, but my eyes can't read "nogpltcp"... wouldn't
> > "bpf_tcp_nogpl" be a bit easier?
>
> Haha, yeah, good point - my eyes also just lump it into a blob...

thanks

>
> >>
> >>  #define min(a, b) ((a) < (b) ? (a) : (b))
> >>
> >> @@ -227,10 +228,53 @@ static void test_dctcp(void)
> >>         bpf_dctcp__destroy(dctcp_skel);
> >>  }
> >>
> >> +static char *err_str = NULL;
> >> +static bool found = false;
> >> +
> >> +static int libbpf_debug_print(enum libbpf_print_level level,
> >> +                             const char *format, va_list args)
> >> +{
> >> +       char *log_buf;
> >> +
> >> +       if (level != LIBBPF_WARN ||
> >> +           strcmp(format, "libbpf: \n%s\n")) {
> >> +               vprintf(format, args);
> >> +               return 0;
> >> +       }
> >> +
> >> +       log_buf = va_arg(args, char *);
> >> +       if (!log_buf)
> >> +               goto out;
> >> +       if (err_str && strstr(log_buf, err_str) != NULL)
> >> +               found = true;
> >> +out:
> >> +       printf(format, log_buf);
> >> +       return 0;
> >> +}
> >> +
> >> +static void test_invalid_license(void)
> >> +{
> >> +       libbpf_print_fn_t old_print_fn = NULL;
> >> +       struct bpf_nogpltcp *skel;
> >> +
> >> +       err_str = "struct ops programs must have a GPL compatible license";
> >> +       old_print_fn = libbpf_set_print(libbpf_debug_print);
> >> +
> >> +       skel = bpf_nogpltcp__open_and_load();
> >> +       if (CHECK(skel, "bpf_nogplgtcp__open_and_load()", "didn't fail\n"))
> >
> > ASSERT_OK_PTR()
> >
> >> +               bpf_nogpltcp__destroy(skel);
> >
> > you should destroy unconditionally
> >
> >> +
> >> +       CHECK(!found, "errmsg check", "expected string '%s'", err_str);
> >
> > ASSERT_EQ(found, true, "expected_err_msg");
> >
> > I can never be sure which way CHECK() is checking
>
> Ah, thanks! I always get confused about CHECK() as well! Maybe it should
> be renamed to ASSERT()? But that would require flipping all the if()
> statements around them as well :/

Exactly, it's the opposite of assert (ASSERT_NOT %-), that
CHECK(!found) is "assert not not found", right?) and it throws me off
every. single. time. Ideally we complete the set of ASSERT_XXX()
macros and convert as much as possible to that. We can also have just
generic ASSERT() for all other complicated cases.

>
> -Toke
>

Re: [PATCH bpf v2 2/2] bpf/selftests: test that kernel rejects a TCP CC with an invalid license

[Toke Høiland-Jørgensen]

Andrii Nakryiko <andrii.nakryiko@gmail.com> writes:


>> Ah, thanks! I always get confused about CHECK() as well! Maybe it should
>> be renamed to ASSERT()? But that would require flipping all the if()
>> statements around them as well :/
>
> Exactly, it's the opposite of assert (ASSERT_NOT %-), that
> CHECK(!found) is "assert not not found", right?) and it throws me off
> every. single. time.

Yup, me too, I have to basically infer the right meaning from the
surrounding if statements (i.e., whether it triggers an error path or
not).

> Ideally we complete the set of ASSERT_XXX() macros and convert as much
> as possible to that. We can also have just generic ASSERT() for all
> other complicated cases.

Totally on board with that! I'll try to remember to fix any selftests I
fiddle with (and not introduce any new uses of CHECK() of course).

-Toke