[bpf-next v6 1/2] bpf: Add bpf_copy_from_user_str kfunc

[bpf-next v6 1/2] bpf: Add bpf_copy_from_user_str kfunc

[Jordan Rome]

This adds a kfunc wrapper around strncpy_from_user,
which can be called from sleepable BPF programs.

This matches the non-sleepable 'bpf_probe_read_user_str'
helper except it includes an additional 'flags'
param, which allows consumers to clear the entire
destination buffer on success.

Signed-off-by: Jordan Rome <linux@jordanrome.com>
---
 include/uapi/linux/bpf.h       |  8 +++++++
 kernel/bpf/helpers.c           | 44 ++++++++++++++++++++++++++++++++++
 tools/include/uapi/linux/bpf.h |  8 +++++++
 3 files changed, 60 insertions(+)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index e05b39e39c3f..5e6be3489e43 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -7513,4 +7513,12 @@ struct bpf_iter_num {
 	__u64 __opaque[1];
 } __attribute__((aligned(8)));

+/*
+ * Flags to control bpf_copy_from_user_str() behaviour.
+ *     - BPF_F_PAD_ZEROS: Memset 0 the tail of the destination buffer on success
+ */
+enum {
+	BPF_F_PAD_ZEROS = (1ULL << 0)
+};
+
 #endif /* _UAPI__LINUX_BPF_H__ */
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index d02ae323996b..a0d2cc8f4f3f 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -2939,6 +2939,49 @@ __bpf_kfunc void bpf_iter_bits_destroy(struct bpf_iter_bits *it)
 	bpf_mem_free(&bpf_global_ma, kit->bits);
 }

+/**
+ * bpf_copy_from_user_str() - Copy a string from an unsafe user address
+ * @dst:             Destination address, in kernel space.  This buffer must be at
+ *                   least @dst__szk bytes long.
+ * @dst__szk:        Maximum number of bytes to copy, including the trailing NUL.
+ * @unsafe_ptr__ign: Source address, in user space.
+ * @flags:           The only supported flag is BPF_F_PAD_ZEROS
+ *
+ * Copies a NUL-terminated string from userspace to BPF space. If user string is
+ * too long this will still ensure zero termination in the dst buffer unless
+ * buffer size is 0.
+ *
+ * If BPF_F_PAD_ZEROS flag is set, memset the tail of @dst to 0 on success and
+ * memset all of @dst on failure.
+ */
+__bpf_kfunc int bpf_copy_from_user_str(void *dst, u32 dst__szk, const void __user *unsafe_ptr__ign, u64 flags)
+{
+	int ret;
+
+	if (unlikely(!dst__szk))
+		return 0;
+
+	if (unlikely(flags & ~BPF_F_PAD_ZEROS))
+		return -EINVAL;
+
+	ret = strncpy_from_user(dst, unsafe_ptr__ign, dst__szk - 1);
+	if (ret < 0) {
+		if (flags & BPF_F_PAD_ZEROS)
+			memset((char *)dst, 0, dst__szk);
+
+		return ret;
+	}
+
+	if (flags & BPF_F_PAD_ZEROS)
+		memset((char *)dst + ret, 0, dst__szk - ret);
+	else
+		((char *)dst)[ret] = '\0';
+
+	ret++;
+
+	return ret;
+}
+
 __bpf_kfunc_end_defs();

 BTF_KFUNCS_START(generic_btf_ids)
@@ -3024,6 +3067,7 @@ BTF_ID_FLAGS(func, bpf_preempt_enable)
 BTF_ID_FLAGS(func, bpf_iter_bits_new, KF_ITER_NEW)
 BTF_ID_FLAGS(func, bpf_iter_bits_next, KF_ITER_NEXT | KF_RET_NULL)
 BTF_ID_FLAGS(func, bpf_iter_bits_destroy, KF_ITER_DESTROY)
+BTF_ID_FLAGS(func, bpf_copy_from_user_str, KF_SLEEPABLE)
 BTF_KFUNCS_END(common_btf_ids)

 static const struct btf_kfunc_id_set common_kfunc_set = {
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index e05b39e39c3f..a8dcb99ed904 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -7513,4 +7513,12 @@ struct bpf_iter_num {
 	__u64 __opaque[1];
 } __attribute__((aligned(8)));

+/*
+ * Flags to control bpf_copy_from_user_str() behaviour.
+ *     - BPF_F_PAD_ZEROS: Memset 0 the entire destination buffer on success
+ */
+enum {
+	BPF_F_PAD_ZEROS = (1ULL << 0)
+};
+
 #endif /* _UAPI__LINUX_BPF_H__ */
--
2.43.5

[bpf-next v6 2/2] bpf: Add tests for bpf_copy_from_user_str kfunc

[Jordan Rome]

This adds tests for both the happy path and
the error path.

Signed-off-by: Jordan Rome <linux@jordanrome.com>
---
 .../selftests/bpf/prog_tests/attach_probe.c   |  8 ++-
 .../selftests/bpf/prog_tests/read_vsyscall.c  |  1 +
 .../selftests/bpf/progs/read_vsyscall.c       |  9 ++-
 .../selftests/bpf/progs/test_attach_probe.c   | 57 ++++++++++++++++++-
 4 files changed, 68 insertions(+), 7 deletions(-)

diff --git a/tools/testing/selftests/bpf/prog_tests/attach_probe.c b/tools/testing/selftests/bpf/prog_tests/attach_probe.c
index 7175af39134f..329c7862b52d 100644
--- a/tools/testing/selftests/bpf/prog_tests/attach_probe.c
+++ b/tools/testing/selftests/bpf/prog_tests/attach_probe.c
@@ -283,9 +283,11 @@ static void test_uprobe_sleepable(struct test_attach_probe *skel)
 	trigger_func3();

 	ASSERT_EQ(skel->bss->uprobe_byname3_sleepable_res, 9, "check_uprobe_byname3_sleepable_res");
-	ASSERT_EQ(skel->bss->uprobe_byname3_res, 10, "check_uprobe_byname3_res");
-	ASSERT_EQ(skel->bss->uretprobe_byname3_sleepable_res, 11, "check_uretprobe_byname3_sleepable_res");
-	ASSERT_EQ(skel->bss->uretprobe_byname3_res, 12, "check_uretprobe_byname3_res");
+	ASSERT_EQ(skel->bss->uprobe_byname3_str_sleepable_res, 10, "check_uprobe_byname3_str_sleepable_res");
+	ASSERT_EQ(skel->bss->uprobe_byname3_res, 11, "check_uprobe_byname3_res");
+	ASSERT_EQ(skel->bss->uretprobe_byname3_sleepable_res, 12, "check_uretprobe_byname3_sleepable_res");
+	ASSERT_EQ(skel->bss->uretprobe_byname3_str_sleepable_res, 13, "check_uretprobe_byname3_str_sleepable_res");
+	ASSERT_EQ(skel->bss->uretprobe_byname3_res, 14, "check_uretprobe_byname3_res");
 }

 void test_attach_probe(void)
diff --git a/tools/testing/selftests/bpf/prog_tests/read_vsyscall.c b/tools/testing/selftests/bpf/prog_tests/read_vsyscall.c
index 3405923fe4e6..c7b9ba8b1d06 100644
--- a/tools/testing/selftests/bpf/prog_tests/read_vsyscall.c
+++ b/tools/testing/selftests/bpf/prog_tests/read_vsyscall.c
@@ -23,6 +23,7 @@ struct read_ret_desc {
 	{ .name = "probe_read_user_str", .ret = -EFAULT },
 	{ .name = "copy_from_user", .ret = -EFAULT },
 	{ .name = "copy_from_user_task", .ret = -EFAULT },
+	{ .name = "copy_from_user_str", .ret = -EFAULT },
 };

 void test_read_vsyscall(void)
diff --git a/tools/testing/selftests/bpf/progs/read_vsyscall.c b/tools/testing/selftests/bpf/progs/read_vsyscall.c
index 986f96687ae1..39ebef430059 100644
--- a/tools/testing/selftests/bpf/progs/read_vsyscall.c
+++ b/tools/testing/selftests/bpf/progs/read_vsyscall.c
@@ -1,5 +1,6 @@
 // SPDX-License-Identifier: GPL-2.0
 /* Copyright (C) 2024. Huawei Technologies Co., Ltd */
+#include "vmlinux.h"
 #include <linux/types.h>
 #include <bpf/bpf_helpers.h>

@@ -7,10 +8,15 @@

 int target_pid = 0;
 void *user_ptr = 0;
-int read_ret[8];
+int read_ret[9];

 char _license[] SEC("license") = "GPL";

+/*
+ * This is the only kfunc, the others are helpers
+ */
+int bpf_copy_from_user_str(void *dst, u32, const void *, u64) __weak __ksym;
+
 SEC("fentry/" SYS_PREFIX "sys_nanosleep")
 int do_probe_read(void *ctx)
 {
@@ -40,6 +46,7 @@ int do_copy_from_user(void *ctx)
 	read_ret[6] = bpf_copy_from_user(buf, sizeof(buf), user_ptr);
 	read_ret[7] = bpf_copy_from_user_task(buf, sizeof(buf), user_ptr,
 					      bpf_get_current_task_btf(), 0);
+	read_ret[8] = bpf_copy_from_user_str((char *)buf, sizeof(buf), user_ptr, 0);

 	return 0;
 }
diff --git a/tools/testing/selftests/bpf/progs/test_attach_probe.c b/tools/testing/selftests/bpf/progs/test_attach_probe.c
index 68466a6ad18c..a40ef14a6614 100644
--- a/tools/testing/selftests/bpf/progs/test_attach_probe.c
+++ b/tools/testing/selftests/bpf/progs/test_attach_probe.c
@@ -5,6 +5,7 @@
 #include <bpf/bpf_helpers.h>
 #include <bpf/bpf_tracing.h>
 #include <bpf/bpf_core_read.h>
+#include <errno.h>
 #include "bpf_misc.h"

 int kprobe2_res = 0;
@@ -14,11 +15,15 @@ int uretprobe_byname_res = 0;
 int uprobe_byname2_res = 0;
 int uretprobe_byname2_res = 0;
 int uprobe_byname3_sleepable_res = 0;
+int uprobe_byname3_str_sleepable_res = 0;
 int uprobe_byname3_res = 0;
 int uretprobe_byname3_sleepable_res = 0;
+int uretprobe_byname3_str_sleepable_res = 0;
 int uretprobe_byname3_res = 0;
 void *user_ptr = 0;

+int bpf_copy_from_user_str(void *dst, u32, const void *, u64) __weak __ksym;
+
 SEC("ksyscall/nanosleep")
 int BPF_KSYSCALL(handle_kprobe_auto, struct __kernel_timespec *req, struct __kernel_timespec *rem)
 {
@@ -87,11 +92,55 @@ static __always_inline bool verify_sleepable_user_copy(void)
 	return bpf_strncmp(data, sizeof(data), "test_data") == 0;
 }

+static __always_inline bool verify_sleepable_user_copy_str(void)
+{
+	int ret;
+	char data_long[20];
+	char data_long_pad[20];
+	char data_long_err[20];
+	char data_short[4];
+	char data_short_pad[4];
+
+	ret = bpf_copy_from_user_str(data_short, sizeof(data_short), user_ptr, 0);
+
+	if (bpf_strncmp(data_short, 4, "tes\0") != 0 || ret != 4)
+		return false;
+
+	ret = bpf_copy_from_user_str(data_short_pad, sizeof(data_short_pad), user_ptr, BPF_F_PAD_ZEROS);
+
+	if (bpf_strncmp(data_short, 4, "tes\0") != 0 || ret != 4)
+		return false;
+
+	ret = bpf_copy_from_user_str(data_long, sizeof(data_long), user_ptr, 0);
+
+	if (bpf_strncmp(data_long, 10, "test_data\0") != 0 || ret != 10)
+		return false;
+
+	ret = bpf_copy_from_user_str(data_long_pad, sizeof(data_long_pad), user_ptr, BPF_F_PAD_ZEROS);
+
+	if (bpf_strncmp(data_long_pad, 10, "test_data\0") != 0 || ret != 10 || data_long_pad[19] != '\0')
+		return false;
+
+	ret = bpf_copy_from_user_str(data_long_err, sizeof(data_long_err), (void *)data_long, BPF_F_PAD_ZEROS);
+
+	if (ret > 0 || data_long_err[9] != '\0')
+		return false;
+
+	ret = bpf_copy_from_user_str(data_long, sizeof(data_long), user_ptr, 2);
+
+	if (ret != -EINVAL)
+		return false;
+
+	return true;
+}
+
 SEC("uprobe.s//proc/self/exe:trigger_func3")
 int handle_uprobe_byname3_sleepable(struct pt_regs *ctx)
 {
 	if (verify_sleepable_user_copy())
 		uprobe_byname3_sleepable_res = 9;
+	if (verify_sleepable_user_copy_str())
+		uprobe_byname3_str_sleepable_res = 10;
 	return 0;
 }

@@ -102,7 +151,7 @@ int handle_uprobe_byname3_sleepable(struct pt_regs *ctx)
 SEC("uprobe//proc/self/exe:trigger_func3")
 int handle_uprobe_byname3(struct pt_regs *ctx)
 {
-	uprobe_byname3_res = 10;
+	uprobe_byname3_res = 11;
 	return 0;
 }

@@ -110,14 +159,16 @@ SEC("uretprobe.s//proc/self/exe:trigger_func3")
 int handle_uretprobe_byname3_sleepable(struct pt_regs *ctx)
 {
 	if (verify_sleepable_user_copy())
-		uretprobe_byname3_sleepable_res = 11;
+		uretprobe_byname3_sleepable_res = 12;
+	if (verify_sleepable_user_copy_str())
+		uretprobe_byname3_str_sleepable_res = 13;
 	return 0;
 }

 SEC("uretprobe//proc/self/exe:trigger_func3")
 int handle_uretprobe_byname3(struct pt_regs *ctx)
 {
-	uretprobe_byname3_res = 12;
+	uretprobe_byname3_res = 14;
 	return 0;
 }

--
2.43.5

Re: [bpf-next v6 1/2] bpf: Add bpf_copy_from_user_str kfunc

[Andrii Nakryiko]

On Sat, Aug 17, 2024 at 5:24 PM Jordan Rome <linux@jordanrome.com> wrote:
>
> This adds a kfunc wrapper around strncpy_from_user,
> which can be called from sleepable BPF programs.
>
> This matches the non-sleepable 'bpf_probe_read_user_str'
> helper except it includes an additional 'flags'
> param, which allows consumers to clear the entire
> destination buffer on success.
>
> Signed-off-by: Jordan Rome <linux@jordanrome.com>
> ---
>  include/uapi/linux/bpf.h       |  8 +++++++
>  kernel/bpf/helpers.c           | 44 ++++++++++++++++++++++++++++++++++
>  tools/include/uapi/linux/bpf.h |  8 +++++++
>  3 files changed, 60 insertions(+)
>

LGTM overall, with the issues pointed out below:

Acked-by: Andrii Nakryiko <andrii@kernel.org>

> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index e05b39e39c3f..5e6be3489e43 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -7513,4 +7513,12 @@ struct bpf_iter_num {
>         __u64 __opaque[1];
>  } __attribute__((aligned(8)));
>
> +/*
> + * Flags to control bpf_copy_from_user_str() behaviour.
> + *     - BPF_F_PAD_ZEROS: Memset 0 the tail of the destination buffer on success

I suspect we might want to reuse this flag for similar kfuncs/helpers
in the future, so I'd generalize description a bit. How about
something like:

BPF_F_PAD_ZEROS: pad destination buffer with zeros. (See respective
helpers documentation for exact details.)

> + */
> +enum {
> +       BPF_F_PAD_ZEROS = (1ULL << 0)
> +};
> +
>  #endif /* _UAPI__LINUX_BPF_H__ */
> diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
> index d02ae323996b..a0d2cc8f4f3f 100644
> --- a/kernel/bpf/helpers.c
> +++ b/kernel/bpf/helpers.c
> @@ -2939,6 +2939,49 @@ __bpf_kfunc void bpf_iter_bits_destroy(struct bpf_iter_bits *it)
>         bpf_mem_free(&bpf_global_ma, kit->bits);
>  }
>
> +/**
> + * bpf_copy_from_user_str() - Copy a string from an unsafe user address
> + * @dst:             Destination address, in kernel space.  This buffer must be at
> + *                   least @dst__szk bytes long.
> + * @dst__szk:        Maximum number of bytes to copy, including the trailing NUL.
> + * @unsafe_ptr__ign: Source address, in user space.
> + * @flags:           The only supported flag is BPF_F_PAD_ZEROS
> + *
> + * Copies a NUL-terminated string from userspace to BPF space. If user string is
> + * too long this will still ensure zero termination in the dst buffer unless
> + * buffer size is 0.
> + *
> + * If BPF_F_PAD_ZEROS flag is set, memset the tail of @dst to 0 on success and
> + * memset all of @dst on failure.
> + */
> +__bpf_kfunc int bpf_copy_from_user_str(void *dst, u32 dst__szk, const void __user *unsafe_ptr__ign, u64 flags)
> +{
> +       int ret;
> +
> +       if (unlikely(!dst__szk))
> +               return 0;
> +
> +       if (unlikely(flags & ~BPF_F_PAD_ZEROS))
> +               return -EINVAL;
> +

let's move this up before dst__szk check, invalid flags should be
rejected regardless of dst__szk

pw-bot: cr

> +       ret = strncpy_from_user(dst, unsafe_ptr__ign, dst__szk - 1);
> +       if (ret < 0) {
> +               if (flags & BPF_F_PAD_ZEROS)
> +                       memset((char *)dst, 0, dst__szk);
> +
> +               return ret;
> +       }
> +
> +       if (flags & BPF_F_PAD_ZEROS)
> +               memset((char *)dst + ret, 0, dst__szk - ret);
> +       else
> +               ((char *)dst)[ret] = '\0';
> +
> +       ret++;
> +
> +       return ret;

nit: return ret + 1;


> +}
> +
>  __bpf_kfunc_end_defs();
>
>  BTF_KFUNCS_START(generic_btf_ids)
> @@ -3024,6 +3067,7 @@ BTF_ID_FLAGS(func, bpf_preempt_enable)
>  BTF_ID_FLAGS(func, bpf_iter_bits_new, KF_ITER_NEW)
>  BTF_ID_FLAGS(func, bpf_iter_bits_next, KF_ITER_NEXT | KF_RET_NULL)
>  BTF_ID_FLAGS(func, bpf_iter_bits_destroy, KF_ITER_DESTROY)
> +BTF_ID_FLAGS(func, bpf_copy_from_user_str, KF_SLEEPABLE)
>  BTF_KFUNCS_END(common_btf_ids)
>
>  static const struct btf_kfunc_id_set common_kfunc_set = {
> diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
> index e05b39e39c3f..a8dcb99ed904 100644
> --- a/tools/include/uapi/linux/bpf.h
> +++ b/tools/include/uapi/linux/bpf.h
> @@ -7513,4 +7513,12 @@ struct bpf_iter_num {
>         __u64 __opaque[1];
>  } __attribute__((aligned(8)));
>
> +/*
> + * Flags to control bpf_copy_from_user_str() behaviour.
> + *     - BPF_F_PAD_ZEROS: Memset 0 the entire destination buffer on success
> + */
> +enum {
> +       BPF_F_PAD_ZEROS = (1ULL << 0)
> +};
> +
>  #endif /* _UAPI__LINUX_BPF_H__ */
> --
> 2.43.5
>

Re: [bpf-next v6 2/2] bpf: Add tests for bpf_copy_from_user_str kfunc

[Andrii Nakryiko]

On Sat, Aug 17, 2024 at 5:24 PM Jordan Rome <linux@jordanrome.com> wrote:
>
> This adds tests for both the happy path and
> the error path.
>
> Signed-off-by: Jordan Rome <linux@jordanrome.com>
> ---
>  .../selftests/bpf/prog_tests/attach_probe.c   |  8 ++-
>  .../selftests/bpf/prog_tests/read_vsyscall.c  |  1 +
>  .../selftests/bpf/progs/read_vsyscall.c       |  9 ++-
>  .../selftests/bpf/progs/test_attach_probe.c   | 57 ++++++++++++++++++-
>  4 files changed, 68 insertions(+), 7 deletions(-)
>

Thanks for adding more test cases! See a small nit below, but otherwise LGTM

Acked-by: Andrii Nakryiko <andrii@kernel.org>

[...]

>
> +static __always_inline bool verify_sleepable_user_copy_str(void)
> +{
> +       int ret;
> +       char data_long[20];
> +       char data_long_pad[20];
> +       char data_long_err[20];
> +       char data_short[4];
> +       char data_short_pad[4];
> +
> +       ret = bpf_copy_from_user_str(data_short, sizeof(data_short), user_ptr, 0);
> +
> +       if (bpf_strncmp(data_short, 4, "tes\0") != 0 || ret != 4)
> +               return false;
> +
> +       ret = bpf_copy_from_user_str(data_short_pad, sizeof(data_short_pad), user_ptr, BPF_F_PAD_ZEROS);
> +
> +       if (bpf_strncmp(data_short, 4, "tes\0") != 0 || ret != 4)
> +               return false;
> +
> +       ret = bpf_copy_from_user_str(data_long, sizeof(data_long), user_ptr, 0);
> +
> +       if (bpf_strncmp(data_long, 10, "test_data\0") != 0 || ret != 10)
> +               return false;
> +
> +       ret = bpf_copy_from_user_str(data_long_pad, sizeof(data_long_pad), user_ptr, BPF_F_PAD_ZEROS);
> +
> +       if (bpf_strncmp(data_long_pad, 10, "test_data\0") != 0 || ret != 10 || data_long_pad[19] != '\0')
> +               return false;
> +
> +       ret = bpf_copy_from_user_str(data_long_err, sizeof(data_long_err), (void *)data_long, BPF_F_PAD_ZEROS);
> +
> +       if (ret > 0 || data_long_err[9] != '\0')

shouldn't the condition be something along the data_long_err[0] !=
'\0' || data_long_err[19] != '\0' to check that the entire buffer is
zeroed out?

> +               return false;
> +
> +       ret = bpf_copy_from_user_str(data_long, sizeof(data_long), user_ptr, 2);
> +
> +       if (ret != -EINVAL)
> +               return false;
> +
> +       return true;
> +}
> +

[...]

Re: [bpf-next v6 2/2] bpf: Add tests for bpf_copy_from_user_str kfunc

[Jordan Rome]

On Mon, Aug 19, 2024 at 6:42 PM Andrii Nakryiko
<andrii.nakryiko@gmail.com> wrote:
>
> On Sat, Aug 17, 2024 at 5:24 PM Jordan Rome <linux@jordanrome.com> wrote:
> >
> > This adds tests for both the happy path and
> > the error path.
> >
> > Signed-off-by: Jordan Rome <linux@jordanrome.com>
> > ---
> >  .../selftests/bpf/prog_tests/attach_probe.c   |  8 ++-
> >  .../selftests/bpf/prog_tests/read_vsyscall.c  |  1 +
> >  .../selftests/bpf/progs/read_vsyscall.c       |  9 ++-
> >  .../selftests/bpf/progs/test_attach_probe.c   | 57 ++++++++++++++++++-
> >  4 files changed, 68 insertions(+), 7 deletions(-)
> >
>
> Thanks for adding more test cases! See a small nit below, but otherwise LGTM
>
> Acked-by: Andrii Nakryiko <andrii@kernel.org>
>
> [...]
>
> >
> > +static __always_inline bool verify_sleepable_user_copy_str(void)
> > +{
> > +       int ret;
> > +       char data_long[20];
> > +       char data_long_pad[20];
> > +       char data_long_err[20];
> > +       char data_short[4];
> > +       char data_short_pad[4];
> > +
> > +       ret = bpf_copy_from_user_str(data_short, sizeof(data_short), user_ptr, 0);
> > +
> > +       if (bpf_strncmp(data_short, 4, "tes\0") != 0 || ret != 4)
> > +               return false;
> > +
> > +       ret = bpf_copy_from_user_str(data_short_pad, sizeof(data_short_pad), user_ptr, BPF_F_PAD_ZEROS);
> > +
> > +       if (bpf_strncmp(data_short, 4, "tes\0") != 0 || ret != 4)
> > +               return false;
> > +
> > +       ret = bpf_copy_from_user_str(data_long, sizeof(data_long), user_ptr, 0);
> > +
> > +       if (bpf_strncmp(data_long, 10, "test_data\0") != 0 || ret != 10)
> > +               return false;
> > +
> > +       ret = bpf_copy_from_user_str(data_long_pad, sizeof(data_long_pad), user_ptr, BPF_F_PAD_ZEROS);
> > +
> > +       if (bpf_strncmp(data_long_pad, 10, "test_data\0") != 0 || ret != 10 || data_long_pad[19] != '\0')
> > +               return false;
> > +
> > +       ret = bpf_copy_from_user_str(data_long_err, sizeof(data_long_err), (void *)data_long, BPF_F_PAD_ZEROS);
> > +
> > +       if (ret > 0 || data_long_err[9] != '\0')
>
> shouldn't the condition be something along the data_long_err[0] !=
> '\0' || data_long_err[19] != '\0' to check that the entire buffer is
> zeroed out?
>

Good catch. I think in a previous iteration `data_long` was only 10
chars long. Will fix.

> > +               return false;
> > +
> > +       ret = bpf_copy_from_user_str(data_long, sizeof(data_long), user_ptr, 2);
> > +
> > +       if (ret != -EINVAL)
> > +               return false;
> > +
> > +       return true;
> > +}
> > +
>
> [...]