[PATCH v1 3/4] sched_setattr: switch to copy_struct_from_user()

Aleksa Sarai
2019-09-25T17:00:27Z

The change is very straightforward, and helps unify the syscall
interface for struct-from-userspace syscalls. Ideally we could also
unify sched_getattr(2)-style syscalls as well, but unfortunately the
correct semantics for such syscalls are much less clear (see [1] for
more detail). In future we could come up with a more sane idea for how
the syscall interface should look.

[1]: commit 1251201c0d34 ("sched/core: Fix uclamp ABI bug, clean up and
robustify sched_read_attr() ABI logic and code")

Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
---
kernel/sched/core.c | 43 +++++++------------------------------------
1 file changed, 7 insertions(+), 36 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index df9f1fe5689b..cdb2f5e29b88 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4900,9 +4900,6 @@ static int sched_copy_attr(struct sched_attr __user *uattr, struct sched_attr *a
u32 size;
int ret;

- if (!access_ok(uattr, SCHED_ATTR_SIZE_VER0))
- return -EFAULT;
-
/* Zero the full structure, so that a short copy will be nice: */
memset(attr, 0, sizeof(*attr));

@@ -4910,45 +4907,19 @@ static int sched_copy_attr(struct sched_attr __user *uattr, struct sched_attr *a
if (ret)
return ret;

- /* Bail out on silly large: */
- if (size > PAGE_SIZE)
- goto err_size;
-
/* ABI compatibility quirk: */
if (!size)
size = SCHED_ATTR_SIZE_VER0;
-
- if (size < SCHED_ATTR_SIZE_VER0)
+ if (size < SCHED_ATTR_SIZE_VER0 || size > PAGE_SIZE)
goto err_size;

- /*
- * If we're handed a bigger struct than we know of,
- * ensure all the unknown bits are 0 - i.e. new
- * user-space does not rely on any kernel feature
- * extensions we dont know about yet.
- */
- if (size > sizeof(*attr)) {
- unsigned char __user *addr;
- unsigned char __user *end;
- unsigned char val;
-
- addr = (void __user *)uattr + sizeof(*attr);
- end = (void __user *)uattr + size;
-
- for (; addr < end; addr++) {
- ret = get_user(val, addr);
- if (ret)
- return ret;
- if (val)
- goto err_size;
- }
- size = sizeof(*attr);
+ ret = copy_struct_from_user(attr, sizeof(*attr), uattr, size);
+ if (ret) {
+ if (ret == -E2BIG)
+ goto err_size;
+ return ret;
}

- ret = copy_from_user(attr, uattr, size);
- if (ret)
- return -EFAULT;
-
if ((attr->sched_flags & SCHED_FLAG_UTIL_CLAMP) &&
size < SCHED_ATTR_SIZE_VER1)
return -EINVAL;
@@ -5148,7 +5119,7 @@ sched_attr_copy_to_user(struct sched_attr __user *uattr,
* sys_sched_getattr - similar to sched_getparam, but with sched_attr
* @pid: the pid in question.
* @uattr: structure containing the extended parameters.
- * @usize: sizeof(attr) that user-space knows about, for forwards and backwards compatibility.
+ * @usize: sizeof(attr) for fwd/bwd comp.
* @flags: for future extension.
*/
SYSCALL_DEFINE4(sched_getattr, pid_t, pid, struct sched_attr __user *, uattr,
--
2.23.0