Code: cifs_find_smb_ses(struct TCP_Server_Info *server, char *username)
 {
	struct list_head *tmp;
 	struct cifsSesInfo *ses;
 
 	write_lock(&cifs_tcp_ses_lock);
	list_for_each(tmp, &server->smb_ses_list) {
		ses = list_entry(tmp, struct cifsSesInfo, smb_ses_list);
		if (strncmp(ses->userName, username, MAX_USERNAME_SIZE))
			continue;
 		++ses->ses_count;
 		write_unlock(&cifs_tcp_ses_lock);
 		return ses;
	}
	write_unlock(&cifs_tcp_ses_lock);
	return NULL;
}

Vulnerability Type: Bypass 
CWE ID: CWE-264
Summary: The cifs_find_smb_ses function in fs/cifs/connect.c in the Linux kernel before 2.6.36 does not properly determine the associations between users and sessions, which allows local users to bypass CIFS share authentication by leveraging a mount of a share by a different user.
Commit Message: cifs: clean up cifs_find_smb_ses (try #2)

This patch replaces the earlier patch by the same name. The only
difference is that MAX_PASSWORD_SIZE has been increased to attempt to
match the limits that windows enforces.

Do a better job of matching sessions by authtype. Matching by username
for a Kerberos session is incorrect, and anonymous sessions need special
handling.

Also, in the case where we do match by username, we also need to match
by password. That ensures that someone else doesn't "borrow" an existing
session without needing to know the password.

Finally, passwords can be longer than 16 bytes. Bump MAX_PASSWORD_SIZE
to 512 to match the size that the userspace mount helper allows.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>