ceph: avoid panic with mismatched symlink sizes in fill_inode()

Return -EINVAL rather than panic if iinfo->symlink_len and inode->i_size
do not match.

Also use kstrndup rather than kmalloc/memcpy.
Signed-off-by: Xi Wang <xi.wang@gmail.com>
Reviewed-by: Alex Elder <elder@dreamhost.com>

fs/ceph/inode.c

@@ -677,18 +677,19 @@ static int fill_inode(struct inode *inode,
 	case S_IFLNK:
 		inode->i_op = &ceph_symlink_iops;
 		if (!ci->i_symlink) {
-			int symlen = iinfo->symlink_len;
+			u32 symlen = iinfo->symlink_len;
 			char *sym;
 
-			BUG_ON(symlen != inode->i_size);
 			spin_unlock(&ci->i_ceph_lock);
 
+			err = -EINVAL;
+			if (WARN_ON(symlen != inode->i_size))
+				goto out;
+
 			err = -ENOMEM;
-			sym = kmalloc(symlen+1, GFP_NOFS);
+			sym = kstrndup(iinfo->symlink, symlen, GFP_NOFS);
 			if (!sym)
 				goto out;
-			memcpy(sym, iinfo->symlink, symlen);
-			sym[symlen] = 0;
 
 			spin_lock(&ci->i_ceph_lock);
 			if (!ci->i_symlink)