[PATCH bpf v2 0/2] Enlarge offset check value in bpf_skb_load_bytes

[PATCH bpf v2 0/2] Enlarge offset check value in bpf_skb_load_bytes

[Liu Jian]

The data length of skb frags + frag_list may be greater than 0xffff,
and skb_header_pointer can not handle negative offset and negative len.
So here INT_MAX is used to check the validity of offset and len.

And add the test case for the change.

Liu Jian (2):
  net: Enlarge offset check value from 0xffff to INT_MAX in
    bpf_skb_load_bytes
  selftests: bpf: add test for skb_load_bytes

 net/core/filter.c                             |  4 +-
 .../selftests/bpf/prog_tests/skb_load_bytes.c | 45 +++++++++++++++++++
 .../selftests/bpf/progs/skb_load_bytes.c      | 19 ++++++++
 3 files changed, 66 insertions(+), 2 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/skb_load_bytes.c
 create mode 100644 tools/testing/selftests/bpf/progs/skb_load_bytes.c

-- 
2.17.1

[PATCH bpf v2 1/2] net: Enlarge offset check value from 0xffff to INT_MAX in bpf_skb_load_bytes

[Liu Jian]

The data length of skb frags + frag_list may be greater than 0xffff,
and skb_header_pointer can not handle negative offset and negative len.
So here INT_MAX is used to check the validity of offset and len.
Add the same change to the related function skb_store_bytes.

Fixes: 05c74e5e53f6 ("bpf: add bpf_skb_load_bytes helper")
Signed-off-by: Liu Jian <liujian56@huawei.com>
Acked-by: Song Liu <songliubraving@fb.com>
---
v1->v2: change nothing, only add Acked-by tag
 net/core/filter.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/core/filter.c b/net/core/filter.c
index 64470a727ef7..1571b6bc51ea 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -1687,7 +1687,7 @@ BPF_CALL_5(bpf_skb_store_bytes, struct sk_buff *, skb, u32, offset,
 
 	if (unlikely(flags & ~(BPF_F_RECOMPUTE_CSUM | BPF_F_INVALIDATE_HASH)))
 		return -EINVAL;
-	if (unlikely(offset > 0xffff))
+	if (unlikely(offset > INT_MAX || len > INT_MAX))
 		return -EFAULT;
 	if (unlikely(bpf_try_make_writable(skb, offset + len)))
 		return -EFAULT;
@@ -1722,7 +1722,7 @@ BPF_CALL_4(bpf_skb_load_bytes, const struct sk_buff *, skb, u32, offset,
 {
 	void *ptr;
 
-	if (unlikely(offset > 0xffff))
+	if (unlikely(offset > INT_MAX || len > INT_MAX))
 		goto err_clear;
 
 	ptr = skb_header_pointer(skb, offset, len, to);
-- 
2.17.1

[PATCH bpf v2 2/2] selftests: bpf: add test for skb_load_bytes

[Liu Jian]

Use bpf_prog_test_run_opts to test the skb_load_bytes function.
Tests the behavior when offset is greater than INT_MAX or a normal value.

Signed-off-by: Liu Jian <liujian56@huawei.com>
---
v1->v2: As Liu Song's review comments, use bpf skeleton and global variable.
 .../selftests/bpf/prog_tests/skb_load_bytes.c | 45 +++++++++++++++++++
 .../selftests/bpf/progs/skb_load_bytes.c      | 19 ++++++++
 2 files changed, 64 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/skb_load_bytes.c
 create mode 100644 tools/testing/selftests/bpf/progs/skb_load_bytes.c

diff --git a/tools/testing/selftests/bpf/prog_tests/skb_load_bytes.c b/tools/testing/selftests/bpf/prog_tests/skb_load_bytes.c
new file mode 100644
index 000000000000..81cc224a0c69
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/skb_load_bytes.c
@@ -0,0 +1,45 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <test_progs.h>
+#include <network_helpers.h>
+#include "skb_load_bytes.skel.h"
+
+void test_skb_load_bytes(void)
+{
+	struct skb_load_bytes *skel;
+	int err, prog_fd, test_result;
+	struct __sk_buff skb = { 0 };
+
+	LIBBPF_OPTS(bpf_test_run_opts, tattr,
+		.data_in = &pkt_v4,
+		.data_size_in = sizeof(pkt_v4),
+		.ctx_in = &skb,
+		.ctx_size_in = sizeof(skb),
+	);
+
+	skel = skb_load_bytes__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "skel_open_and_load"))
+		return;
+
+	prog_fd = bpf_program__fd(skel->progs.skb_process);
+	if (prog_fd < 0)
+		goto out;
+
+	skel->bss->load_offset = (uint32_t)(-1);
+	tattr.data_out = NULL;
+	tattr.data_size_out = 0;
+	err = bpf_prog_test_run_opts(prog_fd, &tattr);
+	CHECK_ATTR(err != 0, "offset -1", "err %d errno %d\n", err, errno);
+	test_result = skel->bss->test_result;
+	CHECK_ATTR(test_result != -EFAULT, "offset -1", "test error\n");
+
+	skel->bss->load_offset = (uint32_t)10;
+	tattr.data_out = NULL;
+	tattr.data_size_out = 0;
+	err = bpf_prog_test_run_opts(prog_fd, &tattr);
+	CHECK_ATTR(err != 0, "offset 10", "err %d errno %d\n", err, errno);
+	test_result = skel->bss->test_result;
+	CHECK_ATTR(test_result != 0, "offset 10", "test error\n");
+
+out:
+	skb_load_bytes__destroy(skel);
+}
diff --git a/tools/testing/selftests/bpf/progs/skb_load_bytes.c b/tools/testing/selftests/bpf/progs/skb_load_bytes.c
new file mode 100644
index 000000000000..e4252fd973be
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/skb_load_bytes.c
@@ -0,0 +1,19 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+
+char _license[] SEC("license") = "GPL";
+
+__u32 load_offset = 0;
+int test_result = 0;
+
+SEC("tc")
+int skb_process(struct __sk_buff *skb)
+{
+	char buf[16];
+
+	test_result = bpf_skb_load_bytes(skb, load_offset, buf, 10);
+
+	return 0;
+}
-- 
2.17.1

Re: [PATCH bpf v2 2/2] selftests: bpf: add test for skb_load_bytes

[Song Liu]

I guess this should go via bpf-next instead? Please mark the patches with
prefix "PATCH bpf-next". 

> On Apr 12, 2022, at 11:21 PM, Liu Jian <liujian56@huawei.com> wrote:
> 
> Use bpf_prog_test_run_opts to test the skb_load_bytes function.
> Tests the behavior when offset is greater than INT_MAX or a normal value.
> 
> Signed-off-by: Liu Jian <liujian56@huawei.com>
> ---
> v1->v2: As Liu Song's review comments, use bpf skeleton and global variable.
> .../selftests/bpf/prog_tests/skb_load_bytes.c | 45 +++++++++++++++++++
> .../selftests/bpf/progs/skb_load_bytes.c      | 19 ++++++++
> 2 files changed, 64 insertions(+)
> create mode 100644 tools/testing/selftests/bpf/prog_tests/skb_load_bytes.c
> create mode 100644 tools/testing/selftests/bpf/progs/skb_load_bytes.c
> 
> diff --git a/tools/testing/selftests/bpf/prog_tests/skb_load_bytes.c b/tools/testing/selftests/bpf/prog_tests/skb_load_bytes.c
> new file mode 100644
> index 000000000000..81cc224a0c69
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/prog_tests/skb_load_bytes.c
> @@ -0,0 +1,45 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#include <test_progs.h>
> +#include <network_helpers.h>
> +#include "skb_load_bytes.skel.h"
> +
> +void test_skb_load_bytes(void)
> +{
> +	struct skb_load_bytes *skel;
> +	int err, prog_fd, test_result;
> +	struct __sk_buff skb = { 0 };
> +
> +	LIBBPF_OPTS(bpf_test_run_opts, tattr,
> +		.data_in = &pkt_v4,
> +		.data_size_in = sizeof(pkt_v4),
> +		.ctx_in = &skb,
> +		.ctx_size_in = sizeof(skb),
> +	);
> +
> +	skel = skb_load_bytes__open_and_load();
> +	if (!ASSERT_OK_PTR(skel, "skel_open_and_load"))
> +		return;
> +
> +	prog_fd = bpf_program__fd(skel->progs.skb_process);
> +	if (prog_fd < 0)
> +		goto out;

I guess we should report error here? like

	if (ASSERT_GE(prog_fd, 0, "prog_fd"))
		goto out;

> +
> +	skel->bss->load_offset = (uint32_t)(-1);
> +	tattr.data_out = NULL;
> +	tattr.data_size_out = 0;
> +	err = bpf_prog_test_run_opts(prog_fd, &tattr);
> +	CHECK_ATTR(err != 0, "offset -1", "err %d errno %d\n", err, errno);

We can use ASSERT_OK() here. 

> +	test_result = skel->bss->test_result;
> +	CHECK_ATTR(test_result != -EFAULT, "offset -1", "test error\n");
And ASSERT_NEQ

> +
> +	skel->bss->load_offset = (uint32_t)10;
> +	tattr.data_out = NULL;
> +	tattr.data_size_out = 0;

I guess = NULL and = 0 are not needed here. 

> +	err = bpf_prog_test_run_opts(prog_fd, &tattr);
> +	CHECK_ATTR(err != 0, "offset 10", "err %d errno %d\n", err, errno);
> +	test_result = skel->bss->test_result;
> +	CHECK_ATTR(test_result != 0, "offset 10", "test error\n");
> +
> +out:
> +	skb_load_bytes__destroy(skel);
> +}
> diff --git a/tools/testing/selftests/bpf/progs/skb_load_bytes.c b/tools/testing/selftests/bpf/progs/skb_load_bytes.c
> new file mode 100644
> index 000000000000..e4252fd973be
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/skb_load_bytes.c
> @@ -0,0 +1,19 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +#include <linux/bpf.h>
> +#include <bpf/bpf_helpers.h>
> +
> +char _license[] SEC("license") = "GPL";
> +
> +__u32 load_offset = 0;
> +int test_result = 0;
> +
> +SEC("tc")
> +int skb_process(struct __sk_buff *skb)
> +{
> +	char buf[16];
> +
> +	test_result = bpf_skb_load_bytes(skb, load_offset, buf, 10);
> +
> +	return 0;
> +}
> -- 
> 2.17.1
> 

Re: [PATCH bpf v2 1/2] net: Enlarge offset check value from 0xffff to INT_MAX in bpf_skb_load_bytes

[Daniel Borkmann]

On 4/13/22 8:21 AM, Liu Jian wrote:
> The data length of skb frags + frag_list may be greater than 0xffff,
> and skb_header_pointer can not handle negative offset and negative len.
> So here INT_MAX is used to check the validity of offset and len.
> Add the same change to the related function skb_store_bytes.
> 
> Fixes: 05c74e5e53f6 ("bpf: add bpf_skb_load_bytes helper")
> Signed-off-by: Liu Jian <liujian56@huawei.com>
> Acked-by: Song Liu <songliubraving@fb.com>
> ---
> v1->v2: change nothing, only add Acked-by tag
>   net/core/filter.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/net/core/filter.c b/net/core/filter.c
> index 64470a727ef7..1571b6bc51ea 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -1687,7 +1687,7 @@ BPF_CALL_5(bpf_skb_store_bytes, struct sk_buff *, skb, u32, offset,
>   
>   	if (unlikely(flags & ~(BPF_F_RECOMPUTE_CSUM | BPF_F_INVALIDATE_HASH)))
>   		return -EINVAL;
> -	if (unlikely(offset > 0xffff))
> +	if (unlikely(offset > INT_MAX || len > INT_MAX))
>   		return -EFAULT;
>   	if (unlikely(bpf_try_make_writable(skb, offset + len)))
>   		return -EFAULT;
> @@ -1722,7 +1722,7 @@ BPF_CALL_4(bpf_skb_load_bytes, const struct sk_buff *, skb, u32, offset,
>   {
>   	void *ptr;
>   
> -	if (unlikely(offset > 0xffff))
> +	if (unlikely(offset > INT_MAX || len > INT_MAX))
>   		goto err_clear;
>   
>   	ptr = skb_header_pointer(skb, offset, len, to);
> 

While at it, lets also change skb_ensure_writable()'s write_len param to unsigned int
type. Both pskb_may_pull() and skb_clone_writable()'s length parameters are of type
unsigned int already.