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Subject[PATCH bpf-next v4 3/3] bpf: use copy_struct_from_user() in bpf() syscall
Date
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")
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/20191009160907.10981-4-christian.brauner@ubuntu.com

/* v2 */
Link: https://lore.kernel.org/r/20191016004138.24845-4-christian.brauner@ubuntu.com
- Alexei Starovoitov <ast@kernel.org>:
- remove unneeded initialization

/* v3 */
Link: https://lore.kernel.org/r/20191016034432.4418-4-christian.brauner@ubuntu.com
unchanged

/* v4 */
- Alexei Starovoitov <ast@kernel.org>:
- move misplaced min after copy_struct_from_user()
---
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 d554ca7671b6..47bf4a81002d 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -2812,21 +2812,18 @@ static int bpf_task_fd_query(const union bpf_attr *attr,

SYSCALL_DEFINE3(bpf, int, cmd, union bpf_attr __user *, uattr, unsigned int, size)
{
- union bpf_attr attr = {};
+ union bpf_attr attr;
int err;

if (sysctl_unprivileged_bpf_disabled && !capable(CAP_SYS_ADMIN))
return -EPERM;

- err = bpf_check_uarg_tail_zero(uattr, sizeof(attr), size);
+ /* copy attributes from user space, may be less than sizeof(bpf_attr) */
+ err = copy_struct_from_user(&attr, sizeof(attr), uattr, 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 = security_bpf(cmd, &attr, size);
if (err < 0)
return err;
--
2.23.0
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