drivers/virt/fsl_hypervisor: Fix error handling path

First, when memory allocation for sg_list_unaligned failed, there
is a bug of calling put_pages() as we haven't pinned any pages.

Second, if get_user_pages_fast() failed we should unpin num_pinned
pages.

This will address both.

As part of these changes, minor update in documentation.

Fixes: 6db71994 ("drivers/virt: introduce Freescale hypervisor management driver")
Signed-off-by: Souptick Joarder <jrdr.linux@gmail.com>
Reviewed-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
Link: https://lore.kernel.org/r/1598995271-6755-1-git-send-email-jrdr.linux@gmail.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/virt/fsl_hypervisor.c

@@ -157,7 +157,7 @@ static long ioctl_memcpy(struct fsl_hv_ioctl_memcpy __user *p)
 
 	unsigned int i;
 	long ret = 0;
-	int num_pinned; /* return value from get_user_pages() */
+	int num_pinned = 0; /* return value from get_user_pages_fast() */
 	phys_addr_t remote_paddr; /* The next address in the remote buffer */
 	uint32_t count; /* The number of bytes left to copy */
 
@@ -174,7 +174,7 @@ static long ioctl_memcpy(struct fsl_hv_ioctl_memcpy __user *p)
 		return -EINVAL;
 
 	/*
-	 * The array of pages returned by get_user_pages() covers only
+	 * The array of pages returned by get_user_pages_fast() covers only
 	 * page-aligned memory.  Since the user buffer is probably not
 	 * page-aligned, we need to handle the discrepancy.
 	 *
@@ -224,7 +224,7 @@ static long ioctl_memcpy(struct fsl_hv_ioctl_memcpy __user *p)
 
 	/*
 	 * 'pages' is an array of struct page pointers that's initialized by
-	 * get_user_pages().
+	 * get_user_pages_fast().
 	 */
 	pages = kcalloc(num_pages, sizeof(struct page *), GFP_KERNEL);
 	if (!pages) {
@@ -241,7 +241,7 @@ static long ioctl_memcpy(struct fsl_hv_ioctl_memcpy __user *p)
 	if (!sg_list_unaligned) {
 		pr_debug("fsl-hv: could not allocate S/G list\n");
 		ret = -ENOMEM;
-		goto exit;
+		goto free_pages;
 	}
 	sg_list = PTR_ALIGN(sg_list_unaligned, sizeof(struct fh_sg_list));
 
@@ -250,7 +250,6 @@ static long ioctl_memcpy(struct fsl_hv_ioctl_memcpy __user *p)
 		num_pages, param.source != -1 ? FOLL_WRITE : 0, pages);
 
 	if (num_pinned != num_pages) {
-		/* get_user_pages() failed */
 		pr_debug("fsl-hv: could not lock source buffer\n");
 		ret = (num_pinned < 0) ? num_pinned : -EFAULT;
 		goto exit;
@@ -292,13 +291,13 @@ static long ioctl_memcpy(struct fsl_hv_ioctl_memcpy __user *p)
 		virt_to_phys(sg_list), num_pages);
 
 exit:
-	if (pages) {
-		for (i = 0; i < num_pages; i++)
-			if (pages[i])
-				put_page(pages[i]);
+	if (pages && (num_pinned > 0)) {
+		for (i = 0; i < num_pinned; i++)
+			put_page(pages[i]);
 	}
 
 	kfree(sg_list_unaligned);
+free_pages:
 	kfree(pages);
 
 	if (!ret)