reiserfs: Check the return value from __getblk()

__getblk() can return a NULL pointer if we run out of memory or if we
try to access beyond the end of the device; check it and handle it
appropriately.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Link: https://lore.kernel.org/lkml/CAFcO6XOacq3hscbXevPQP7sXRoYFz34ZdKPYjmd6k5sZuhGFDw@mail.gmail.com/
Tested-by: butt3rflyh4ck <butterflyhuangxx@gmail.com>
Fixes: 1da177e4c3 ("Linux-2.6.12-rc2") # probably introduced in 2002
Acked-by: Edward Shishkin <edward.shishkin@gmail.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>

fs/reiserfs/journal.c

@@ -2326,7 +2326,7 @@ static struct buffer_head *reiserfs_breada(struct block_device *dev,
 	int i, j;
 
 	bh = __getblk(dev, block, bufsize);
-	if (buffer_uptodate(bh))
+	if (!bh || buffer_uptodate(bh))
 		return (bh);
 
 	if (block + BUFNR > max_block) {
@@ -2336,6 +2336,8 @@ static struct buffer_head *reiserfs_breada(struct block_device *dev,
 	j = 1;
 	for (i = 1; i < blocks; i++) {
 		bh = __getblk(dev, block + i, bufsize);
+		if (!bh)
+			break;
 		if (buffer_uptodate(bh)) {
 			brelse(bh);
 			break;