Re: [PATCH] per-user signal pending and message queue limits

[Chris Wright]

* Marcelo Tosatti (marcelo.tosatti@xxxxxxxxxxxx) wrote:
> This should be OK for inclusion into -mm now, if no other comment is made.

This patch doesn't account for sigqueue bits properly.  The allocations
aren't always made in task context.  So, it's trivial to illegitimately
drain off the new signal_pending counter, leaving the potential for the
original DoS unfixed.  And the setuid issues still seem to be there,
right?

Couple other nits below:

Some bits need to be converted to tabs from spaces.

> diff -Nur --show-c-function a/linux-2.6.5/include/asm-s390/resource.h linux-2.6.5/include/asm-s390/resource.h
> --- a/linux-2.6.5/include/asm-s390/resource.h	2004-04-04 00:36:55.000000000 -0300
> +++ linux-2.6.5/include/asm-s390/resource.h	2004-04-27 08:32:46.000000000 -0300
> @@ -24,7 +24,9 @@
>  #define RLIMIT_MEMLOCK	8		/* max locked-in-memory address space */
>  #define RLIMIT_AS	9		/* address space limit */
>  #define RLIMIT_LOCKS	10		/* maximum file locks held */
> -  
> +#define RLIMIT_SIGPENDING 11            /* max number of pending signals */
> +#define RLIMIT_MSGQUEUE 12              /* max number of POSIX msg queues */
> +
>  #define RLIM_NLIMITS	11

Missed this one.

> diff -Nur --show-c-function a/linux-2.6.5/include/asm-sparc/resource.h linux-2.6.5/include/asm-sparc/resource.h
> --- a/linux-2.6.5/include/asm-sparc/resource.h	2004-04-04 00:36:18.000000000 -0300
> +++ linux-2.6.5/include/asm-sparc/resource.h	2004-04-27 08:32:46.000000000 -0300
> @@ -22,8 +22,10 @@
>  #define RLIMIT_MEMLOCK  8               /* max locked-in-memory address space */
>  #define RLIMIT_AS       9               /* address space limit */
>  #define RLIMIT_LOCKS	10		/* maximum file locks held */
> +#define RLIMIT_SIGPENDING 11            /* max number of pending signals */
> +#define RLIMIT_MSGQUEUE 12              /* max number of POSIX msg queues */
>  
> -#define RLIM_NLIMITS	11
> +#define RLIM_NLIMITS	13
>  
>  /*
>   * SuS says limits have to be unsigned.
> @@ -45,6 +47,9 @@
>      {RLIM_INFINITY, RLIM_INFINITY},	\
>      {RLIM_INFINITY, RLIM_INFINITY},	\
>      {RLIM_INFINITY, RLIM_INFINITY}	\
> +    {MAX_USER_SIGNALS, MAX_USER_SIGNALS}, \
> +    {MAX_USER_MSGQUEUE, MAX_USER_MSGQUEUE},\

Won't compile.

> diff -Nur --show-c-function a/linux-2.6.5/include/asm-sparc64/resource.h linux-2.6.5/include/asm-sparc64/resource.h
> --- a/linux-2.6.5/include/asm-sparc64/resource.h	2004-04-04 00:36:15.000000000 -0300
> +++ linux-2.6.5/include/asm-sparc64/resource.h	2004-04-27 08:32:46.000000000 -0300
> @@ -22,8 +22,10 @@
>  #define RLIMIT_MEMLOCK  8               /* max locked-in-memory address space */
>  #define RLIMIT_AS       9               /* address space limit */
>  #define RLIMIT_LOCKS	10		/* maximum file locks held */
> +#define RLIMIT_SIGPENDING 11            /* max number of pending signals */
> +#define RLIMIT_MSGQUEUE 12              /* max number of POSIX msg queues */
>  
> -#define RLIM_NLIMITS	11
> +#define RLIM_NLIMITS	13
>  
>  /*
>   * SuS says limits have to be unsigned.
> @@ -44,6 +46,8 @@
>      {RLIM_INFINITY, RLIM_INFINITY},	\
>      {RLIM_INFINITY, RLIM_INFINITY},	\
>      {RLIM_INFINITY, RLIM_INFINITY}	\
> +    {MAX_USER_SIGNALS, MAX_USER_SIGNALS}, \
> +    {MAX_USER_MSGQUEUE, MAX_USER_MSGQUEUE},\

Ditto.

> +++ linux-2.6.5/include/linux/signal.h	2004-04-27 08:32:46.000000000 -0300
> @@ -7,6 +7,10 @@
>  #include <asm/siginfo.h>
>  
>  #ifdef __KERNEL__
> +
> +#define MAX_QUEUED_SIGNALS	4096

Besides right below, is this really used anymore?

> +#define MAX_USER_SIGNALS	(MAX_QUEUED_SIGNALS/4)

here.

> diff -Nur --show-c-function a/linux-2.6.5/kernel/signal.c linux-2.6.5/kernel/signal.c
> --- a/linux-2.6.5/kernel/signal.c	2004-04-27 09:53:24.000000000 -0300
> +++ linux-2.6.5/kernel/signal.c	2004-04-27 11:05:08.000000000 -0300
> @@ -31,8 +31,7 @@
>  
>  static kmem_cache_t *sigqueue_cachep;
>  
> -atomic_t nr_queued_signals;
> -int max_queued_signals = 1024;
> +int max_queued_signals = MAX_QUEUED_SIGNALS;

and here, but max_queued_signals is no longer really relevant, right?
Should we removed both nr_queued_signals and max_queued_signals and the
associated sysctl's?  Or leave it, and give CAP_SYS_RESOURCE the ability
to do a full override?  I chose the latter, although I'm inclined to
drop that bit.

>  static void flush_sigqueue(struct sigpending *queue)
> @@ -700,11 +707,13 @@ static int send_signal(int sig, struct s
>  	   make sure at least one signal gets delivered and don't
>  	   pass on the info struct.  */
>  
> -	if (atomic_read(&nr_queued_signals) < max_queued_signals)
> +	if (atomic_read(&current->user->signal_pending) <=

current may not be valid here.

I have a diff between your patch and what I'm testing, but it's
cluttered a bit by the fact that I've also merged it up to 2.6.6-rc3
I can send you the full patch if that's easier.

thanks,
-chris
-- 
Linux Security Modules     http://lsm.immunix.org     http://lsm.bkbits.net
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