misc: xilinx-sdfec: improve get_user_pages_fast() error handling

This fixes the case of get_user_pages_fast() returning a -errno.
The result needs to be stored in a signed integer. And for safe
signed/unsigned comparisons, it's best to keep everything signed.
And get_user_pages_fast() also expects a signed value for number
of pages to pin.

Therefore, change most relevant variables, from u32 to int. Leave
"n" unsigned, for convenience in checking for overflow. And provide
a WARN_ON_ONCE() and early return, if overflow occurs.

Also, as long as we're tidying up: rename the page array from page,
to pages, in order to match the conventions used in most other call
sites.

Fixes: 20ec628e ("misc: xilinx_sdfec: Add ability to configure LDPC")
Cc: Derek Kiernan <derek.kiernan@xilinx.com>
Cc: Dragan Cvetic <dragan.cvetic@xilinx.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Michal Simek <michal.simek@xilinx.com>
Cc: linux-arm-kernel@lists.infradead.org
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
Link: https://lore.kernel.org/r/20200527012628.1100649-2-jhubbard@nvidia.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/misc/xilinx_sdfec.c

@@ -602,10 +602,10 @@ static int xsdfec_table_write(struct xsdfec_dev *xsdfec, u32 offset,
 			      const u32 depth)
 {
 	u32 reg = 0;
-	u32 res;
-	u32 n, i;
+	int res, i, nr_pages;
+	u32 n;
 	u32 *addr = NULL;
-	struct page *page[MAX_NUM_PAGES];
+	struct page *pages[MAX_NUM_PAGES];
 
 	/*
 	 * Writes that go beyond the length of
@@ -622,15 +622,22 @@ static int xsdfec_table_write(struct xsdfec_dev *xsdfec, u32 offset,
 	if ((len * XSDFEC_REG_WIDTH_JUMP) % PAGE_SIZE)
 		n += 1;
 
-	res = get_user_pages_fast((unsigned long)src_ptr, n, 0, page);
-	if (res < n) {
+	if (WARN_ON_ONCE(n > INT_MAX))
+		return -EINVAL;
+
+	nr_pages = n;
+
+	res = get_user_pages_fast((unsigned long)src_ptr, nr_pages, 0, pages);
+	if (res < nr_pages) {
+		if (res > 0) {
 			for (i = 0; i < res; i++)
-			put_page(page[i]);
+				put_page(pages[i]);
+		}
 		return -EINVAL;
 	}
 
-	for (i = 0; i < n; i++) {
-		addr = kmap(page[i]);
+	for (i = 0; i < nr_pages; i++) {
+		addr = kmap(pages[i]);
 		do {
 			xsdfec_regwrite(xsdfec,
 					base_addr + ((offset + reg) *
@@ -639,7 +646,7 @@ static int xsdfec_table_write(struct xsdfec_dev *xsdfec, u32 offset,
 			reg++;
 		} while ((reg < len) &&
 			 ((reg * XSDFEC_REG_WIDTH_JUMP) % PAGE_SIZE));
-		put_page(page[i]);
+		put_page(pages[i]);
 	}
 	return reg;
 }