[PATCH 3/3] bpf: use copy_struct_from_user() in bpf() syscall

Christian Brauner
2019-10-09T16:09:33Z

In v5.4-rc2 we added a new helper (cf. [1]) copy_struct_from_user().
This helper is intended for all codepaths that copy structs from
userspace that are versioned by size. The bpf() syscall does exactly
what copy_struct_from_user() is doing.
Note that copy_struct_from_user() is calling min() already. So
technically, the min_t() call could go. But the size is used further
below so leave it.

[1]: f5a1a536fa14 ("lib: introduce copy_struct_from_user() helper")
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
---
kernel/bpf/syscall.c | 9 +++------
1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 6f4f9097b1fe..6fdcbdb27501 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -2819,14 +2819,11 @@ SYSCALL_DEFINE3(bpf, int, cmd, union bpf_attr __user *, uattr, unsigned int, siz
if (sysctl_unprivileged_bpf_disabled && !capable(CAP_SYS_ADMIN))
return -EPERM;

- err = bpf_check_uarg_tail_zero(uattr, sizeof(attr), size);
- if (err)
- return err;
size = min_t(u32, size, sizeof(attr));
-
/* copy attributes from user space, may be less than sizeof(bpf_attr) */
- if (copy_from_user(&attr, uattr, size) != 0)
- return -EFAULT;
+ err = copy_struct_from_user(&attr, sizeof(attr), uattr, size);
+ if (err)
+ return err;

err = security_bpf(cmd, &attr, size);
if (err < 0)
--
2.23.0