cifs: extra sanity checking for cifs.idmap keys

Now that we aren't so rigid about the length of the key being passed
in, we need to be a bit more rigorous about checking the length of
the actual data against the claimed length (a'la num_subauths field).

Check for the case where userspace sends us a seemingly valid key
with a num_subauths field that goes beyond the end of the array. If
that happens, return -EIO and invalidate the key.

Also change the other places where we check for malformed keys in this
code to invalidate the key as well.

Reviewed-by: Shirish Pargaonkar <shirishpargaonkar@gmail.com>
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <smfrench@gmail.com>

1 files changed, 18 insertions, 2 deletions

diff --git a/fs/cifs/cifsacl.c b/fs/cifs/cifsacl.c
index 751d34bd825c..b0b114acdece 100644
--- a/fs/cifs/cifsacl.c
+++ b/fs/cifs/cifsacl.c
@@ -191,6 +191,8 @@ id_to_sid(unsigned int cid, uint sidtype, struct cifs_sid *ssid)
 {
         int rc;
         struct key *sidkey;
+        struct cifs_sid *ksid;
+        unsigned int ksid_size;
         char desc[3 + 10 + 1]; /* 3 byte prefix + 10 bytes for value + NULL */
         const struct cred *saved_cred;
 
@@ -211,14 +213,27 @@ id_to_sid(unsigned int cid, uint sidtype, struct cifs_sid *ssid)
                 rc = -EIO;
                 cFYI(1, "%s: Downcall contained malformed key "
                         "(datalen=%hu)", __func__, sidkey->datalen);
-                goto out_key_put;
+                goto invalidate_key;
         }
-        cifs_copy_sid(ssid, (struct cifs_sid *)sidkey->payload.data);
+
+        ksid = (struct cifs_sid *)sidkey->payload.data;
+        ksid_size = CIFS_SID_BASE_SIZE + (ksid->num_subauth * sizeof(__le32));
+        if (ksid_size > sidkey->datalen) {
+                rc = -EIO;
+                cFYI(1, "%s: Downcall contained malformed key (datalen=%hu, "
+                        "ksid_size=%u)", __func__, sidkey->datalen, ksid_size);
+                goto invalidate_key;
+        }
+        cifs_copy_sid(ssid, ksid);
 out_key_put:
         key_put(sidkey);
 out_revert_creds:
         revert_creds(saved_cred);
         return rc;
+
+invalidate_key:
+        key_invalidate(sidkey);
+        goto out_key_put;
 }
 
 static int
@@ -264,6 +279,7 @@ sid_to_id(struct cifs_sb_info *cifs_sb, struct cifs_sid *psid,
                 rc = -EIO;
                 cFYI(1, "%s: Downcall contained malformed key "
                         "(datalen=%hu)", __func__, sidkey->datalen);
+                key_invalidate(sidkey);
                 goto out_key_put;
         }