[PATCH 1/3] fs: ocfs2: Fix possible null-pointer dereferences in ocfs2_xa_prepare_entry()

[Jia-Ju Bai <baijiaju1990@gmail.com>]

In ocfs2_xa_prepare_entry(), there is an if statement on line 2136 to
check whether loc->xl_entry is NULL:
    if (loc->xl_entry)

When loc->xl_entry is NULL, it is used on line 2158:
    ocfs2_xa_add_entry(loc, name_hash);
        loc->xl_entry->xe_name_hash = cpu_to_le32(name_hash);
        loc->xl_entry->xe_name_offset = cpu_to_le16(loc->xl_size);
and line 2164:
	ocfs2_xa_add_namevalue(loc, xi);
        loc->xl_entry->xe_value_size = cpu_to_le64(xi->xi_value_len);
        loc->xl_entry->xe_name_len = xi->xi_name_len;

Thus, possible null-pointer dereferences may occur.

To fix these bugs, if loc-xl_entry is NULL, ocfs2_xa_prepare_entry() 
abnormally returns with -EINVAL.

These bugs are found by a static analysis tool STCheck written by us.

Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com>
---
 fs/ocfs2/xattr.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/fs/ocfs2/xattr.c b/fs/ocfs2/xattr.c
index 385f3aaa2448..f690502daf3c 100644
--- a/fs/ocfs2/xattr.c
+++ b/fs/ocfs2/xattr.c
@@ -2154,8 +2154,10 @@ static int ocfs2_xa_prepare_entry(struct ocfs2_xa_loc *loc,
 			}
 		}
 		ocfs2_xa_wipe_namevalue(loc);
-	} else
-		ocfs2_xa_add_entry(loc, name_hash);
+	} else {
+		rc = -EINVAL;
+		goto out;
+	}
 
 	/*
 	 * If we get here, we have a blank entry.  Fill it.  We grow our
-- 
2.17.0