iov_iter: refactor rw_copy_check_uvector and import_iovec

Split rw_copy_check_uvector into two new helpers with more sensible
calling conventions:

 - iovec_from_user copies a iovec from userspace either into the provided
   stack buffer if it fits, or allocates a new buffer for it.  Returns
   the actually used iovec.  It also verifies that iov_len does fit a
   signed type, and handles compat iovecs if the compat flag is set.
 - __import_iovec consolidates the native and compat versions of
   import_iovec. It calls iovec_from_user, then validates each iovec
   actually points to user addresses, and ensures the total length
   doesn't overflow.

This has two major implications:

 - the access_process_vm case loses the total lenght checking, which
   wasn't required anyway, given that each call receives two iovecs
   for the local and remote side of the operation, and it verifies
   the total length on the local side already.
 - instead of a single loop there now are two loops over the iovecs.
   Given that the iovecs are cache hot this doesn't make a major
   difference

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 5 insertions, 11 deletions

diff --git a/include/linux/compat.h b/include/linux/compat.h
index 790be5ffc12c..cebcaac68aec 100644
--- a/include/linux/compat.h
+++ b/include/linux/compat.h
@@ -91,6 +91,11 @@
 	static inline long __do_compat_sys##name(__MAP(x,__SC_DECL,__VA_ARGS__))
 #endif /* COMPAT_SYSCALL_DEFINEx */
 
+struct compat_iovec {
+	compat_uptr_t	iov_base;
+	compat_size_t	iov_len;
+};
+
 #ifdef CONFIG_COMPAT
 
 #ifndef compat_user_stack_pointer
@@ -248,11 +253,6 @@ typedef struct compat_siginfo {
 	} _sifields;
 } compat_siginfo_t;
 
-struct compat_iovec {
-	compat_uptr_t	iov_base;
-	compat_size_t	iov_len;
-};
-
 struct compat_rlimit {
 	compat_ulong_t	rlim_cur;
 	compat_ulong_t	rlim_max;
@@ -451,12 +451,6 @@ extern long compat_arch_ptrace(struct task_struct *child, compat_long_t request,
 
 struct epoll_event;	/* fortunately, this one is fixed-layout */
 
-extern ssize_t compat_rw_copy_check_uvector(int type,
-		const struct compat_iovec __user *uvector,
-		unsigned long nr_segs,
-		unsigned long fast_segs, struct iovec *fast_pointer,
-		struct iovec **ret_pointer);
-
 extern void __user *compat_alloc_user_space(unsigned long len);
 
 int compat_restore_altstack(const compat_stack_t __user *uss);