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

Christian Brauner
2019-10-09T16:09:19Z

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")
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
---
kernel/bpf/syscall.c | 22 +++++++---------------
1 file changed, 7 insertions(+), 15 deletions(-)

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 82eabd4e38ad..78790778f101 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -63,30 +63,22 @@ 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;
+ size_t size = min(expected_size, actual_size);
+ size_t rest = max(expected_size, actual_size) - size;
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;
+ err = check_zeroed_user(uaddr + expected_size, rest);
+ if (err < 0)
+ return err;

- for (; addr < end; addr++) {
- err = get_user(val, addr);
- if (err)
- return err;
- if (val)
- return -E2BIG;
- }
+ if (err)
+ return -E2BIG;

return 0;
}
--
2.23.0