BACKPORT: Smack: File receive for sockets

The existing file receive hook checks for access on
the file inode even for UDS. This is not right, as
the inode is not used by Smack to make access checks
for sockets. This change checks for an appropriate
access relationship between the receiving (current)
process and the socket. If the process can't write
to the socket's send label or the socket's receive
label can't write to the process fail.

This will allow the legitimate cases, where the
socket sender and socket receiver can freely communicate.
Only strangly set socket labels should cause a problem.

Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
(cherry-picked from upstream 79be093500791cc25cc31bcaec5a4db62e21497b)

diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
index fe3c77411bb691f7e5e49b8782fd48476f46b741..8b4a00562475dbf86813b37f12e33a7b483d9dc2 100644 (file)
--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -1863,12 +1863,34 @@ static int smack_file_receive(struct file *file)
        int may = 0;
        struct smk_audit_info ad;
        struct inode *inode = file_inode(file);
+       struct socket *sock;
+       struct task_smack *tsp;
+       struct socket_smack *ssp;
 
        if (unlikely(IS_PRIVATE(inode)))
                return 0;
 
        smk_ad_init(&ad, __func__, LSM_AUDIT_DATA_PATH);
        smk_ad_setfield_u_fs_path(&ad, file->f_path);
+
+       if (S_ISSOCK(inode->i_mode)) {
+               sock = SOCKET_I(inode);
+               ssp = sock->sk->sk_security;
+               tsp = current_security();
+               /*
+                * If the receiving process can't write to the
+                * passed socket or if the passed socket can't
+                * write to the receiving process don't accept
+                * the passed socket.
+                */
+               rc = smk_access(tsp->smk_task, ssp->smk_out, MAY_WRITE, &ad);
+               rc = smk_bu_file(file, may, rc);
+               if (rc < 0)
+                       return rc;
+               rc = smk_access(ssp->smk_in, tsp->smk_task, MAY_WRITE, &ad);
+               rc = smk_bu_file(file, may, rc);
+               return rc;
+       }
        /*
         * This code relies on bitmasks.
         */