nilfs2: avoid overflowing segment numbers in nilfs_ioctl_clean_segments()

nsegs is read from userspace.  Limit its value and avoid overflowing nsegs
* sizeof(__u64) in the subsequent call to memdup_user().

This patch complements 481fe17e ("nilfs2: potential integer overflow
in nilfs_ioctl_clean_segments()").
Signed-off-by: NXi Wang <xi.wang@gmail.com>
Cc: Haogang Chen <haogangchen@gmail.com>
Acked-by: NRyusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

fs/nilfs2/ioctl.c

@@ -603,6 +603,8 @@ static int nilfs_ioctl_clean_segments(struct inode *inode, struct file *filp,
 	nsegs = argv[4].v_nmembs;
 	if (argv[4].v_size != argsz[4])
 		goto out;
+	if (nsegs > UINT_MAX / sizeof(__u64))
+		goto out;
 
 	/*
 	 * argv[4] points to segment numbers this ioctl cleans.  We