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

[Jia-Ju Bai]

On 2019/7/26 17:37, Joseph Qi wrote:

On 19/7/26 11:36, Jia-Ju Bai wrote:

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 <baijiaju1...@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;
+       }

Since entry not found, so there is nothing to do in
ocfs2_xa_prepare_entry(). We may change it like:

if (!loc->xl_entry) {
        rc = -EINVAL;
        goto out;
}       

if (ocfs2_xa_can_reuse_entry(loc, xi)) {
        ......
}
.....

Okay, I will send a v2 patch.


Best wishes,
Jia-Ju Bai