Callers of clnt_tli_create(3) can specify that an arbitrary port number be dynamically assigned for the client socket being created. clnt_tli_create(3) tries bindresvport(3) first in this case. bindresvport(3) chooses a reserved port if the caller has CAP_NET_ADMIN_BIND privilege. If this fails, bind(2) is used to assign a port number from the range above 1024. This approach becomes a problem whenever bindresvport(3) happens to choose the port number of a well-known service. If the caller is a long-running service (like rpc.statd), it indefinitely prevents the IANA-assigned well-known service from starting. When using the AUTH_SYS authentication flavor, RPC services can use the remote client's port number to determine whether the client is privileged, and thus the UID and GID numbers in the RPC are trustworthy. However, it's pretty easy for a man-in-the-middle to replace these while the RPC is in flight anyway. The port number provides no actual security. Therefore, remove the bindresvport step to prevent svc_tli_create(3) from choosing a port number that interferes with well-known services assigned to a privileged port. clnt_tli_create(3) will now never assign a privileged port dynamically. If needed, a caller may still bind to a dynamically- assigned reserved port by invoking bindresvport(3) directly and passing the already-bound file descriptor to clnt_tli_create(3). But that should be a special case. It is no longer the default behavior. BugLink: https://bugzilla.linux-nfs.org/show_bug.cgi?id=320 Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx> --- src/clnt_generic.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/src/clnt_generic.c b/src/clnt_generic.c index 3f3dabf..e5a314f 100644 --- a/src/clnt_generic.c +++ b/src/clnt_generic.c @@ -47,6 +47,7 @@ extern bool_t __rpc_is_local_host(const char *); int __rpc_raise_fd(int); +extern int __binddynport(int fd); #ifndef NETIDLEN #define NETIDLEN 32 @@ -340,7 +341,8 @@ clnt_tli_create(int fd, const struct netconfig *nconf, servtype = nconf->nc_semantics; if (!__rpc_fd2sockinfo(fd, &si)) goto err; - bindresvport(fd, NULL); + if (__binddynport(fd) == -1) + goto err; } else { if (!__rpc_fd2sockinfo(fd, &si)) goto err; -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
