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hurd: Improve reply port handling when exiting signal handlers

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If we're doing signals, that means we've already got the signal thread
running, and that implies TLS having been set up. So we know that
__hurd_local_reply_port will resolve to THREAD_SELF->reply_port, and can
access that directly using the THREAD_GETMEM and THREAD_SETMEM macros.
This avoids potential miscompilations, and should also be a tiny bit
faster.

Also, use mach_port_mod_refs () and not mach_port_destroy () to destroy
the receive right. mach_port_destroy () should *never* be used on
mach_task_self (); this can easily lead to port use-after-free
vulnerabilities if the task has any other references to the same port.

Signed-off-by: Sergey Bugaev <bugaevc@gmail.com>
Message-Id: <20230319151017.531737-26-bugaevc@gmail.com>
This commit is contained in:
Sergey Bugaev 2023-03-19 18:10:08 +03:00 committed by Samuel Thibault
parent b37899d34d
commit 747812349d
2 changed files with 16 additions and 29 deletions
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24
hurd/sigunwind.c
View File

@ -18,7 +18,6 @@
#include <hurd.h> #include <hurd.h>
#include <thread_state.h> #include <thread_state.h>
#include <hurd/threadvar.h>
#include <jmpbuf-unwind.h> #include <jmpbuf-unwind.h>
#include <assert.h> #include <assert.h>
#include <stdint.h> #include <stdint.h>
@ -39,19 +38,18 @@ _hurdsig_longjmp_from_handler (void *data, jmp_buf env, int val)
{ {
/* Destroy the MiG reply port used by the signal handler, and restore /* Destroy the MiG reply port used by the signal handler, and restore
the reply port in use by the thread when interrupted. */ the reply port in use by the thread when interrupted. */
mach_port_t *reply_port = &__hurd_local_reply_port; mach_port_t reply_port = THREAD_GETMEM (THREAD_SELF, reply_port);
if (*reply_port) /* Assigning MACH_PORT_DEAD here tells libc's mig_get_reply_port not to
{ get another reply port, but avoids mig_dealloc_reply_port trying to
mach_port_t port = *reply_port; deallocate it after the receive fails (which it will, because the
/* Assigning MACH_PORT_DEAD here tells libc's mig_get_reply_port reply port will be bogus, regardless). */
not to get another reply port, but avoids mig_dealloc_reply_port THREAD_SETMEM (THREAD_SELF, reply_port, MACH_PORT_DEAD);
trying to deallocate it after the receive fails (which it will, if (MACH_PORT_VALID (reply_port))
because the reply port will be bogus, regardless). */ __mach_port_mod_refs (__mach_task_self (), reply_port,
*reply_port = MACH_PORT_DEAD; MACH_PORT_RIGHT_RECEIVE, -1);
__mach_port_destroy (__mach_task_self (), port);
}
if (scp->sc_reply_port) if (scp->sc_reply_port)
__mach_port_destroy (__mach_task_self (), scp->sc_reply_port); __mach_port_mod_refs (__mach_task_self (), scp->sc_reply_port,
MACH_PORT_RIGHT_RECEIVE, -1);
} }
__spin_lock (&ss->lock); __spin_lock (&ss->lock);

21
sysdeps/mach/hurd/i386/sigreturn.c
View File

@ -19,7 +19,6 @@ register int *sp asm ("%esp");
#include <hurd.h> #include <hurd.h>
#include <hurd/signal.h> #include <hurd/signal.h>
#include <hurd/threadvar.h>
#include <hurd/msg.h> #include <hurd/msg.h>
#include <stdlib.h> #include <stdlib.h>
#include <string.h> #include <string.h>
@ -59,7 +58,7 @@ __sigreturn (struct sigcontext *scp)
{ {
struct hurd_sigstate *ss; struct hurd_sigstate *ss;
struct hurd_userlink *link = (void *) &scp[1]; struct hurd_userlink *link = (void *) &scp[1];
mach_port_t *reply_port; mach_port_t reply_port;
if (scp == NULL || (scp->sc_mask & _SIG_CANT_MASK)) if (scp == NULL || (scp->sc_mask & _SIG_CANT_MASK))
{ {
@ -101,20 +100,10 @@ __sigreturn (struct sigcontext *scp)
/* Destroy the MiG reply port used by the signal handler, and restore the /* Destroy the MiG reply port used by the signal handler, and restore the
reply port in use by the thread when interrupted. */ reply port in use by the thread when interrupted. */
reply_port = &__hurd_local_reply_port; reply_port = THREAD_GETMEM (THREAD_SELF, reply_port);
if (*reply_port) THREAD_SETMEM (THREAD_SELF, reply_port, scp->sc_reply_port);
{ __mach_port_mod_refs (__mach_task_self (), reply_port,
mach_port_t port = *reply_port; MACH_PORT_RIGHT_RECEIVE, -1);
/* Assigning MACH_PORT_DEAD here tells libc's mig_get_reply_port not to
get another reply port, but avoids mig_dealloc_reply_port trying to
deallocate it after the receive fails (which it will, because the
reply port will be bogus, whether we do this or not). */
*reply_port = MACH_PORT_DEAD;
__mach_port_destroy (__mach_task_self (), port);
}
*reply_port = scp->sc_reply_port;
if (scp->sc_fpused) if (scp->sc_fpused)
/* Restore the FPU state. Mach conveniently stores the state /* Restore the FPU state. Mach conveniently stores the state