iov_iter: move rw_copy_check_uvector() into lib/iov_iter.c

This lets the compiler inline it into import_iovec() generating
much better code.

Signed-off-by: David Laight <david.laight@aculab.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 176 insertions, 0 deletions

diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index 5e40786c8f123..ccea9db3f72be 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -1651,6 +1651,109 @@ const void *dup_iter(struct iov_iter *new, struct iov_iter *old, gfp_t flags)
 EXPORT_SYMBOL(dup_iter);
 
 /**
+ * rw_copy_check_uvector() - Copy an array of &struct iovec from userspace
+ *     into the kernel and check that it is valid.
+ *
+ * @type: One of %CHECK_IOVEC_ONLY, %READ, or %WRITE.
+ * @uvector: Pointer to the userspace array.
+ * @nr_segs: Number of elements in userspace array.
+ * @fast_segs: Number of elements in @fast_pointer.
+ * @fast_pointer: Pointer to (usually small on-stack) kernel array.
+ * @ret_pointer: (output parameter) Pointer to a variable that will point to
+ *     either @fast_pointer, a newly allocated kernel array, or NULL,
+ *     depending on which array was used.
+ *
+ * This function copies an array of &struct iovec of @nr_segs from
+ * userspace into the kernel and checks that each element is valid (e.g.
+ * it does not point to a kernel address or cause overflow by being too
+ * large, etc.).
+ *
+ * As an optimization, the caller may provide a pointer to a small
+ * on-stack array in @fast_pointer, typically %UIO_FASTIOV elements long
+ * (the size of this array, or 0 if unused, should be given in @fast_segs).
+ *
+ * @ret_pointer will always point to the array that was used, so the
+ * caller must take care not to call kfree() on it e.g. in case the
+ * @fast_pointer array was used and it was allocated on the stack.
+ *
+ * Return: The total number of bytes covered by the iovec array on success
+ *   or a negative error code on error.
+ */
+ssize_t rw_copy_check_uvector(int type, const struct iovec __user *uvector,
+		unsigned long nr_segs, unsigned long fast_segs,
+		struct iovec *fast_pointer, struct iovec **ret_pointer)
+{
+	unsigned long seg;
+	ssize_t ret;
+	struct iovec *iov = fast_pointer;
+
+	/*
+	 * SuS says "The readv() function *may* fail if the iovcnt argument
+	 * was less than or equal to 0, or greater than {IOV_MAX}.  Linux has
+	 * traditionally returned zero for zero segments, so...
+	 */
+	if (nr_segs == 0) {
+		ret = 0;
+		goto out;
+	}
+
+	/*
+	 * First get the "struct iovec" from user memory and
+	 * verify all the pointers
+	 */
+	if (nr_segs > UIO_MAXIOV) {
+		ret = -EINVAL;
+		goto out;
+	}
+	if (nr_segs > fast_segs) {
+		iov = kmalloc_array(nr_segs, sizeof(struct iovec), GFP_KERNEL);
+		if (iov == NULL) {
+			ret = -ENOMEM;
+			goto out;
+		}
+	}
+	if (copy_from_user(iov, uvector, nr_segs*sizeof(*uvector))) {
+		ret = -EFAULT;
+		goto out;
+	}
+
+	/*
+	 * According to the Single Unix Specification we should return EINVAL
+	 * if an element length is < 0 when cast to ssize_t or if the
+	 * total length would overflow the ssize_t return value of the
+	 * system call.
+	 *
+	 * Linux caps all read/write calls to MAX_RW_COUNT, and avoids the
+	 * overflow case.
+	 */
+	ret = 0;
+	for (seg = 0; seg < nr_segs; seg++) {
+		void __user *buf = iov[seg].iov_base;
+		ssize_t len = (ssize_t)iov[seg].iov_len;
+
+		/* see if we we're about to use an invalid len or if
+		 * it's about to overflow ssize_t */
+		if (len < 0) {
+			ret = -EINVAL;
+			goto out;
+		}
+		if (type >= 0
+		    && unlikely(!access_ok(buf, len))) {
+			ret = -EFAULT;
+			goto out;
+		}
+		if (len > MAX_RW_COUNT - ret) {
+			len = MAX_RW_COUNT - ret;
+			iov[seg].iov_len = len;
+		}
+		ret += len;
+	}
+out:
+	*ret_pointer = iov;
+	return ret;
+}
+
+/**
  * import_iovec() - Copy an array of &struct iovec from userspace
  *     into the kernel, check that it is valid, and initialize a new
  *     &struct iov_iter iterator to access it.
@@ -1695,6 +1798,79 @@ EXPORT_SYMBOL(import_iovec);
 #ifdef CONFIG_COMPAT
 #include <linux/compat.h>
 
+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)
+{
+	compat_ssize_t tot_len;
+	struct iovec *iov = *ret_pointer = fast_pointer;
+	ssize_t ret = 0;
+	int seg;
+
+	/*
+	 * SuS says "The readv() function *may* fail if the iovcnt argument
+	 * was less than or equal to 0, or greater than {IOV_MAX}.  Linux has
+	 * traditionally returned zero for zero segments, so...
+	 */
+	if (nr_segs == 0)
+		goto out;
+
+	ret = -EINVAL;
+	if (nr_segs > UIO_MAXIOV)
+		goto out;
+	if (nr_segs > fast_segs) {
+		ret = -ENOMEM;
+		iov = kmalloc_array(nr_segs, sizeof(struct iovec), GFP_KERNEL);
+		if (iov == NULL)
+			goto out;
+	}
+	*ret_pointer = iov;
+
+	ret = -EFAULT;
+	if (!access_ok(uvector, nr_segs*sizeof(*uvector)))
+		goto out;
+
+	/*
+	 * Single unix specification:
+	 * We should -EINVAL if an element length is not >= 0 and fitting an
+	 * ssize_t.
+	 *
+	 * In Linux, the total length is limited to MAX_RW_COUNT, there is
+	 * no overflow possibility.
+	 */
+	tot_len = 0;
+	ret = -EINVAL;
+	for (seg = 0; seg < nr_segs; seg++) {
+		compat_uptr_t buf;
+		compat_ssize_t len;
+
+		if (__get_user(len, &uvector->iov_len) ||
+		   __get_user(buf, &uvector->iov_base)) {
+			ret = -EFAULT;
+			goto out;
+		}
+		if (len < 0)	/* size_t not fitting in compat_ssize_t .. */
+			goto out;
+		if (type >= 0 &&
+		    !access_ok(compat_ptr(buf), len)) {
+			ret = -EFAULT;
+			goto out;
+		}
+		if (len > MAX_RW_COUNT - tot_len)
+			len = MAX_RW_COUNT - tot_len;
+		tot_len += len;
+		iov->iov_base = compat_ptr(buf);
+		iov->iov_len = (compat_size_t) len;
+		uvector++;
+		iov++;
+	}
+	ret = tot_len;
+
+out:
+	return ret;
+}
+
 ssize_t compat_import_iovec(int type,
 		const struct compat_iovec __user * uvector,
 		unsigned nr_segs, unsigned fast_segs,