perf_event_open: switch to copy_struct_from_user()

Switch perf_event_open() syscall from it's own copying
struct perf_event_attr from userspace to the new dedicated
copy_struct_from_user() helper.

The change is very straightforward, and helps unify the syscall
interface for struct-from-userspace syscalls.

Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Christian Brauner <christian.brauner@ubuntu.com>
[christian.brauner@ubuntu.com: improve commit message]
Link: https://lore.kernel.org/r/20191001011055.19283-5-cyphar@cyphar.com
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

1 files changed, 9 insertions, 38 deletions

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 4655adbbae10..3f0cb82e4fbc 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -10586,55 +10586,26 @@ static int perf_copy_attr(struct perf_event_attr __user *uattr,
         u32 size;
         int ret;
 
-        if (!access_ok(uattr, PERF_ATTR_SIZE_VER0))
-                return -EFAULT;
-
-        /*
-         * zero the full structure, so that a short copy will be nice.
-         */
+        /* Zero the full structure, so that a short copy will be nice. */
         memset(attr, 0, sizeof(*attr));
 
         ret = get_user(size, &uattr->size);
         if (ret)
                 return ret;
 
-        if (size > PAGE_SIZE)   /* silly large */
-                goto err_size;
-
-        if (!size)              /* abi compat */
+        /* ABI compatibility quirk: */
+        if (!size)
                 size = PERF_ATTR_SIZE_VER0;
-
-        if (size < PERF_ATTR_SIZE_VER0)
+        if (size < PERF_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;
-
         attr->size = size;
 
         if (attr->__reserved_1)