Re: [Libtirpc-devel] [PATCH 1/1] Fix DoS vulnerability in statd and mountd

[Steve Dickson <steved@xxxxxxxxxx>]

Hello,

On 8/7/21 1:02 PM, Dai Ngo wrote:
> Currently my_svc_run does not handle poll time allowing idle TCP
> connections to remain ESTABLISHED indefinitely. When the number
> of connections reaches the limit the open file descriptors
> (ulimit -n) then accept(2) fails with EMFILE. Since libtirpc does
> not handle EMFILE returned from accept(2) this get my_svc_run into
> a tight loop calling accept(2) resulting in the RPC service being
> down, it's no longer able to service any requests.
>
> Fix by removing idle connections when select(2) times out in my_svc_run
> and when open(2) returns EMFILE/ENFILE in auth_reload.
>
> Signed-off-by: dai.ngo@xxxxxxxxxx
> ---
>   support/export/auth.c  | 12 ++++++++++--
>   utils/mountd/svc_run.c | 10 ++++++++--
>   utils/statd/svc_run.c  | 11 ++++++++---
>   3 files changed, 26 insertions(+), 7 deletions(-)
>
> diff --git a/support/export/auth.c b/support/export/auth.c
> index 03ce4b8a0e1e..0bb189fb4037 100644
> --- a/support/export/auth.c
> +++ b/support/export/auth.c
> @@ -81,6 +81,8 @@ check_useipaddr(void)
>   		cache_flush();
>   }
>   
> +extern void __svc_destroy_idle(int, bool_t);
This is adding to the API... Which means mountd
and statd (the next patch) will not compile without
this new API...

Does this mean an SONAME change? That is such a pain!

steved.

> +
>   unsigned int
>   auth_reload()
>   {
> @@ -91,8 +93,14 @@ auth_reload()
>   	int			fd;
>   
>   	if ((fd = open(etab.statefn, O_RDONLY)) < 0) {
> -		xlog(L_FATAL, "couldn't open %s", etab.statefn);
> -	} else if (fstat(fd, &stb) < 0) {
> +		if (errno != EMFILE && errno != ENFILE)
> +			xlog(L_FATAL, "couldn't open %s", etab.statefn);
> +		/* remove idle */
> +		__svc_destroy_idle(5, FALSE);
> +		if ((fd = open(etab.statefn, O_RDONLY)) < 0)
> +			xlog(L_FATAL, "couldn't open %s", etab.statefn);
> +	}
> +	if (fstat(fd, &stb) < 0) {
>   		xlog(L_FATAL, "couldn't stat %s", etab.statefn);
>   		close(fd);
>   	} else if (last_fd != -1 && stb.st_ino == last_inode) {
> diff --git a/utils/mountd/svc_run.c b/utils/mountd/svc_run.c
> index 167b9757bde2..ada8d0ac8844 100644
> --- a/utils/mountd/svc_run.c
> +++ b/utils/mountd/svc_run.c
> @@ -59,6 +59,7 @@
>   #include "export.h"
>   
>   void my_svc_run(void);
> +extern void __svc_destroy_idle(int , bool_t);
>   
>   #if defined(__GLIBC__) && LONG_MAX != INT_MAX
>   /* bug in glibc 2.3.6 and earlier, we need
> @@ -95,6 +96,7 @@ my_svc_run(void)
>   {
>   	fd_set	readfds;
>   	int	selret;
> +	struct	timeval tv;
>   
>   	for (;;) {
>   
> @@ -102,8 +104,10 @@ my_svc_run(void)
>   		cache_set_fds(&readfds);
>   		v4clients_set_fds(&readfds);
>   
> +		tv.tv_sec = 30;
> +		tv.tv_usec = 0;
>   		selret = select(FD_SETSIZE, &readfds,
> -				(void *) 0, (void *) 0, (struct timeval *) 0);
> +				(void *) 0, (void *) 0, &tv);
>   
>   
>   		switch (selret) {
> @@ -113,7 +117,9 @@ my_svc_run(void)
>   				continue;
>   			xlog(L_ERROR, "my_svc_run() - select: %m");
>   			return;
> -
> +		case 0:
> +			__svc_destroy_idle(30, FALSE);
> +			continue;
>   		default:
>   			selret -= cache_process_req(&readfds);
>   			selret -= v4clients_process(&readfds);
> diff --git a/utils/statd/svc_run.c b/utils/statd/svc_run.c
> index e343c7689860..8888788c81d0 100644
> --- a/utils/statd/svc_run.c
> +++ b/utils/statd/svc_run.c
> @@ -59,6 +59,7 @@
>   
>   void my_svc_exit(void);
>   static int	svc_stop = 0;
> +extern void __svc_destroy_idle(int , bool_t);
>   
>   /*
>    * This is the global notify list onto which all SM_NOTIFY and CALLBACK
> @@ -85,6 +86,7 @@ my_svc_run(int sockfd)
>   	FD_SET_TYPE	readfds;
>   	int             selret;
>   	time_t		now;
> +	struct timeval	tv;
>   
>   	svc_stop = 0;
>   
> @@ -101,7 +103,6 @@ my_svc_run(int sockfd)
>   		/* Set notify sockfd for waiting for reply */
>   		FD_SET(sockfd, &readfds);
>   		if (notify) {
> -			struct timeval	tv;
>   
>   			tv.tv_sec  = NL_WHEN(notify) - now;
>   			tv.tv_usec = 0;
> @@ -111,8 +112,10 @@ my_svc_run(int sockfd)
>   				(void *) 0, (void *) 0, &tv);
>   		} else {
>   			xlog(D_GENERAL, "Waiting for client connections");
> +			tv.tv_sec = 30;
> +			tv.tv_usec = 0;
>   			selret = select(FD_SETSIZE, &readfds,
> -				(void *) 0, (void *) 0, (struct timeval *) 0);
> +				(void *) 0, (void *) 0, &tv);
>   		}
>   
>   		switch (selret) {
> @@ -124,7 +127,9 @@ my_svc_run(int sockfd)
>   			return;
>   
>   		case 0:
> -			/* A notify/callback timed out. */
> +			/* A notify/callback/wait for client timed out. */
> +			if (!notify)
> +				__svc_destroy_idle(30, FALSE);
>   			continue;
>   
>   		default: