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    SubjectRe: [PATCH] per-user signal pending and message queue limits
    * Marcelo Tosatti (marcelo.tosatti@cyclades.com) 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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