[PATCH bpf-next v4 1/3] bpf: use check_zeroed_user() in bpf_check_uarg_tail_zero()

Christian Brauner
2019-10-16T11:19:39Z

In v5.4-rc2 we added a new helper (cf. [1]) check_zeroed_user() which
does what bpf_check_uarg_tail_zero() is doing generically. We're slowly
switching such codepaths over to use check_zeroed_user() instead of
using their own hand-rolled version.

[1]: f5a1a536fa14 ("lib: introduce copy_struct_from_user() helper")
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Aleksa Sarai <cyphar@cyphar.com>
Cc: bpf@vger.kernel.org
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
---
/* v1 */
Link: https://lore.kernel.org/r/20191009160907.10981-2-christian.brauner@ubuntu.com

/* v2 */
Link: https://lore.kernel.org/r/20191016004138.24845-2-christian.brauner@ubuntu.com
- Alexei Starovoitov <ast@kernel.org>:
- Add a comment in bpf_check_uarg_tail_zero() to clarify that
copy_struct_from_user() should be used whenever possible instead.

/* v3 */
Link: https://lore.kernel.org/r/20191016034432.4418-2-christian.brauner@ubuntu.com
- Christian Brauner <christian.brauner@ubuntu.com>:
- use correct checks for check_zeroed_user()

/* v4 */
- Alexei Starovoitov <ast@kernel.org>:
- remove unnecessary min() and max() calls
---
kernel/bpf/syscall.c | 23 +++++++----------------
1 file changed, 7 insertions(+), 16 deletions(-)

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 82eabd4e38ad..8d112bc069c0 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -58,35 +58,26 @@ static const struct bpf_map_ops * const bpf_map_types[] = {
* There is a ToCToU between this function call and the following
* copy_from_user() call. However, this is not a concern since this function is
* meant to be a future-proofing of bits.
+ *
+ * Note, instead of using bpf_check_uarg_tail_zero() followed by
+ * copy_from_user() use the dedicated copy_struct_from_user() helper which
+ * performs both tasks whenever possible.
*/
int bpf_check_uarg_tail_zero(void __user *uaddr,
size_t expected_size,
size_t actual_size)
{
- unsigned char __user *addr;
- unsigned char __user *end;
- unsigned char val;
int err;

if (unlikely(actual_size > PAGE_SIZE)) /* silly large */
return -E2BIG;

- if (unlikely(!access_ok(uaddr, actual_size)))
- return -EFAULT;
-
if (actual_size <= expected_size)
return 0;

- addr = uaddr + expected_size;
- end = uaddr + actual_size;
-
- for (; addr < end; addr++) {
- err = get_user(val, addr);
- if (err)
- return err;
- if (val)
- return -E2BIG;
- }
+ err = check_zeroed_user(uaddr + expected_size, actual_size - expected_size);
+ if (err <= 0)
+ return err ?: -E2BIG;

return 0;
}
--
2.23.0