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nptl: Move setxid broadcast implementation into libc

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The signal handler is exported as __nptl_setxid_sighandler, so
that the libpthread initialization code can install it.  This
is sufficient for now because it is guarantueed to happen before
the first pthread_create call.
This commit is contained in:
Florian Weimer 2021-04-21 19:49:51 +02:00
parent 08129b155e
commit 486010a3c8
9 changed files with 287 additions and 287 deletions
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1
nptl/Makefile
View File

@ -47,6 +47,7 @@ routines = \
lowlevellock \
nptl_deallocate_tsd \
nptl_nthreads \
nptl_setxid \
old_pthread_cond_broadcast \
old_pthread_cond_destroy \
old_pthread_cond_init \

1
nptl/Versions
View File

@ -147,6 +147,7 @@ libc {
__mutex_aconf;
__nptl_deallocate_tsd;
__nptl_nthreads;
__nptl_setxid_sighandler;
__pthread_attr_copy;
__pthread_attr_destroy;
__pthread_attr_init;

209
nptl/allocatestack.c
View File

@ -953,215 +953,6 @@ __reclaim_stacks (void)
}
static void
setxid_mark_thread (struct xid_command *cmdp, struct pthread *t)
{
int ch;
/* Wait until this thread is cloned. */
if (t->setxid_futex == -1
&& ! atomic_compare_and_exchange_bool_acq (&t->setxid_futex, -2, -1))
do
futex_wait_simple (&t->setxid_futex, -2, FUTEX_PRIVATE);
while (t->setxid_futex == -2);
/* Don't let the thread exit before the setxid handler runs. */
t->setxid_futex = 0;
do
{
ch = t->cancelhandling;
/* If the thread is exiting right now, ignore it. */
if ((ch & EXITING_BITMASK) != 0)
{
/* Release the futex if there is no other setxid in
progress. */
if ((ch & SETXID_BITMASK) == 0)
{
t->setxid_futex = 1;
futex_wake (&t->setxid_futex, 1, FUTEX_PRIVATE);
}
return;
}
}
while (atomic_compare_and_exchange_bool_acq (&t->cancelhandling,
ch | SETXID_BITMASK, ch));
}
static void
setxid_unmark_thread (struct xid_command *cmdp, struct pthread *t)
{
int ch;
do
{
ch = t->cancelhandling;
if ((ch & SETXID_BITMASK) == 0)
return;
}
while (atomic_compare_and_exchange_bool_acq (&t->cancelhandling,
ch & ~SETXID_BITMASK, ch));
/* Release the futex just in case. */
t->setxid_futex = 1;
futex_wake (&t->setxid_futex, 1, FUTEX_PRIVATE);
}
static int
setxid_signal_thread (struct xid_command *cmdp, struct pthread *t)
{
if ((t->cancelhandling & SETXID_BITMASK) == 0)
return 0;
int val;
pid_t pid = __getpid ();
val = INTERNAL_SYSCALL_CALL (tgkill, pid, t->tid, SIGSETXID);
/* If this failed, it must have had not started yet or else exited. */
if (!INTERNAL_SYSCALL_ERROR_P (val))
{
atomic_increment (&cmdp->cntr);
return 1;
}
else
return 0;
}
/* Check for consistency across set*id system call results. The abort
should not happen as long as all privileges changes happen through
the glibc wrappers. ERROR must be 0 (no error) or an errno
code. */
void
attribute_hidden
__nptl_setxid_error (struct xid_command *cmdp, int error)
{
do
{
int olderror = cmdp->error;
if (olderror == error)
break;
if (olderror != -1)
{
/* Mismatch between current and previous results. Save the
error value to memory so that is not clobbered by the
abort function and preserved in coredumps. */
volatile int xid_err __attribute__((unused)) = error;
abort ();
}
}
while (atomic_compare_and_exchange_bool_acq (&cmdp->error, error, -1));
}
int
attribute_hidden
__nptl_setxid (struct xid_command *cmdp)
{
int signalled;
int result;
lll_lock (GL (dl_stack_cache_lock), LLL_PRIVATE);
__xidcmd = cmdp;
cmdp->cntr = 0;
cmdp->error = -1;
struct pthread *self = THREAD_SELF;
/* Iterate over the list with system-allocated threads first. */
list_t *runp;
list_for_each (runp, &GL (dl_stack_used))
{
struct pthread *t = list_entry (runp, struct pthread, list);
if (t == self)
continue;
setxid_mark_thread (cmdp, t);
}
/* Now the list with threads using user-allocated stacks. */
list_for_each (runp, &GL (dl_stack_user))
{
struct pthread *t = list_entry (runp, struct pthread, list);
if (t == self)
continue;
setxid_mark_thread (cmdp, t);
}
/* Iterate until we don't succeed in signalling anyone. That means
we have gotten all running threads, and their children will be
automatically correct once started. */
do
{
signalled = 0;
list_for_each (runp, &GL (dl_stack_used))
{
struct pthread *t = list_entry (runp, struct pthread, list);
if (t == self)
continue;
signalled += setxid_signal_thread (cmdp, t);
}
list_for_each (runp, &GL (dl_stack_user))
{
struct pthread *t = list_entry (runp, struct pthread, list);
if (t == self)
continue;
signalled += setxid_signal_thread (cmdp, t);
}
int cur = cmdp->cntr;
while (cur != 0)
{
futex_wait_simple ((unsigned int *) &cmdp->cntr, cur,
FUTEX_PRIVATE);
cur = cmdp->cntr;
}
}
while (signalled != 0);
/* Clean up flags, so that no thread blocks during exit waiting
for a signal which will never come. */
list_for_each (runp, &GL (dl_stack_used))
{
struct pthread *t = list_entry (runp, struct pthread, list);
if (t == self)
continue;
setxid_unmark_thread (cmdp, t);
}
list_for_each (runp, &GL (dl_stack_user))
{
struct pthread *t = list_entry (runp, struct pthread, list);
if (t == self)
continue;
setxid_unmark_thread (cmdp, t);
}
/* This must be last, otherwise the current thread might not have
permissions to send SIGSETXID syscall to the other threads. */
result = INTERNAL_SYSCALL_NCS (cmdp->syscall_no, 3,
cmdp->id[0], cmdp->id[1], cmdp->id[2]);
int error = 0;
if (__glibc_unlikely (INTERNAL_SYSCALL_ERROR_P (result)))
{
error = INTERNAL_SYSCALL_ERRNO (result);
__set_errno (error);
result = -1;
}
__nptl_setxid_error (cmdp, error);
lll_unlock (GL (dl_stack_cache_lock), LLL_PRIVATE);
return result;
}
static inline void __attribute__((always_inline))
init_one_static_tls (struct pthread *curp, struct link_map *map)
{

49
nptl/nptl-init.c
View File

@ -52,7 +52,6 @@ static const char nptl_version[] __attribute_used__ = VERSION;
#ifdef SHARED
static const struct pthread_functions pthread_functions =
{
.ptr__nptl_setxid = __nptl_setxid,
};
# define ptr_pthread_functions &pthread_functions
#else
@ -106,52 +105,6 @@ sigcancel_handler (int sig, siginfo_t *si, void *ctx)
}
struct xid_command *__xidcmd attribute_hidden;
/* We use the SIGSETXID signal in the setuid, setgid, etc. implementations to
tell each thread to call the respective setxid syscall on itself. This is
the handler. */
static void
sighandler_setxid (int sig, siginfo_t *si, void *ctx)
{
int result;
/* Safety check. It would be possible to call this function for
other signals and send a signal from another process. This is not
correct and might even be a security problem. Try to catch as
many incorrect invocations as possible. */
if (sig != SIGSETXID
|| si->si_pid != __getpid ()
|| si->si_code != SI_TKILL)
return;
result = INTERNAL_SYSCALL_NCS (__xidcmd->syscall_no, 3, __xidcmd->id[0],
__xidcmd->id[1], __xidcmd->id[2]);
int error = 0;
if (__glibc_unlikely (INTERNAL_SYSCALL_ERROR_P (result)))
error = INTERNAL_SYSCALL_ERRNO (result);
__nptl_setxid_error (__xidcmd, error);
/* Reset the SETXID flag. */
struct pthread *self = THREAD_SELF;
int flags, newval;
do
{
flags = THREAD_GETMEM (self, cancelhandling);
newval = THREAD_ATOMIC_CMPXCHG_VAL (self, cancelhandling,
flags & ~SETXID_BITMASK, flags);
}
while (flags != newval);
/* And release the futex. */
self->setxid_futex = 1;
futex_wake (&self->setxid_futex, 1, FUTEX_PRIVATE);
if (atomic_decrement_val (&__xidcmd->cntr) == 0)
futex_wake ((unsigned int *) &__xidcmd->cntr, 1, FUTEX_PRIVATE);
}
/* When using __thread for this, we do it in libc so as not
to give libpthread its own TLS segment just for this. */
extern void **__libc_dl_error_tsd (void) __attribute__ ((const));
@ -183,7 +136,7 @@ __pthread_initialize_minimal_internal (void)
(void) __libc_sigaction (SIGCANCEL, &sa, NULL);
/* Install the handle to change the threads' uid/gid. */
sa.sa_sigaction = sighandler_setxid;
sa.sa_sigaction = __nptl_setxid_sighandler;
sa.sa_flags = SA_SIGINFO | SA_RESTART;
(void) __libc_sigaction (SIGSETXID, &sa, NULL);

279
nptl/nptl_setxid.c Normal file
View File

@ -0,0 +1,279 @@
/* Copyright (C) 2002-2021 Free Software Foundation, Inc.
This file is part of the GNU C Library.
Contributed by Ulrich Drepper <drepper@redhat.com>, 2002.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
#include <futex-internal.h>
#include <ldsodefs.h>
#include <list.h>
#include <lowlevellock.h>
#include <pthreadP.h>
#include <unistd.h>
/* Check for consistency across set*id system call results. The abort
should not happen as long as all privileges changes happen through
the glibc wrappers. ERROR must be 0 (no error) or an errno
code. */
static void
setxid_error (struct xid_command *cmdp, int error)
{
do
{
int olderror = cmdp->error;
if (olderror == error)
break;
if (olderror != -1)
{
/* Mismatch between current and previous results. Save the
error value to memory so that is not clobbered by the
abort function and preserved in coredumps. */
volatile int xid_err __attribute__ ((unused)) = error;
abort ();
}
}
while (atomic_compare_and_exchange_bool_acq (&cmdp->error, error, -1));
}
/* Set by __nptl_setxid and used by __nptl_setxid_sighandler. */
static struct xid_command *xidcmd;
/* We use the SIGSETXID signal in the setuid, setgid, etc. implementations to
tell each thread to call the respective setxid syscall on itself. This is
the handler. */
void
__nptl_setxid_sighandler (int sig, siginfo_t *si, void *ctx)
{
int result;
/* Safety check. It would be possible to call this function for
other signals and send a signal from another process. This is not
correct and might even be a security problem. Try to catch as
many incorrect invocations as possible. */
if (sig != SIGSETXID
|| si->si_pid != __getpid ()
|| si->si_code != SI_TKILL)
return;
result = INTERNAL_SYSCALL_NCS (xidcmd->syscall_no, 3, xidcmd->id[0],
xidcmd->id[1], xidcmd->id[2]);
int error = 0;
if (__glibc_unlikely (INTERNAL_SYSCALL_ERROR_P (result)))
error = INTERNAL_SYSCALL_ERRNO (result);
setxid_error (xidcmd, error);
/* Reset the SETXID flag. */
struct pthread *self = THREAD_SELF;
int flags, newval;
do
{
flags = THREAD_GETMEM (self, cancelhandling);
newval = THREAD_ATOMIC_CMPXCHG_VAL (self, cancelhandling,
flags & ~SETXID_BITMASK, flags);
}
while (flags != newval);
/* And release the futex. */
self->setxid_futex = 1;
futex_wake (&self->setxid_futex, 1, FUTEX_PRIVATE);
if (atomic_decrement_val (&xidcmd->cntr) == 0)
futex_wake ((unsigned int *) &xidcmd->cntr, 1, FUTEX_PRIVATE);
}
libc_hidden_def (__nptl_setxid_sighandler)
static void
setxid_mark_thread (struct xid_command *cmdp, struct pthread *t)
{
int ch;
/* Wait until this thread is cloned. */
if (t->setxid_futex == -1
&& ! atomic_compare_and_exchange_bool_acq (&t->setxid_futex, -2, -1))
do
futex_wait_simple (&t->setxid_futex, -2, FUTEX_PRIVATE);
while (t->setxid_futex == -2);
/* Don't let the thread exit before the setxid handler runs. */
t->setxid_futex = 0;
do
{
ch = t->cancelhandling;
/* If the thread is exiting right now, ignore it. */
if ((ch & EXITING_BITMASK) != 0)
{
/* Release the futex if there is no other setxid in
progress. */
if ((ch & SETXID_BITMASK) == 0)
{
t->setxid_futex = 1;
futex_wake (&t->setxid_futex, 1, FUTEX_PRIVATE);
}
return;
}
}
while (atomic_compare_and_exchange_bool_acq (&t->cancelhandling,
ch | SETXID_BITMASK, ch));
}
static void
setxid_unmark_thread (struct xid_command *cmdp, struct pthread *t)
{
int ch;
do
{
ch = t->cancelhandling;
if ((ch & SETXID_BITMASK) == 0)
return;
}
while (atomic_compare_and_exchange_bool_acq (&t->cancelhandling,
ch & ~SETXID_BITMASK, ch));
/* Release the futex just in case. */
t->setxid_futex = 1;
futex_wake (&t->setxid_futex, 1, FUTEX_PRIVATE);
}
static int
setxid_signal_thread (struct xid_command *cmdp, struct pthread *t)
{
if ((t->cancelhandling & SETXID_BITMASK) == 0)
return 0;
int val;
pid_t pid = __getpid ();
val = INTERNAL_SYSCALL_CALL (tgkill, pid, t->tid, SIGSETXID);
/* If this failed, it must have had not started yet or else exited. */
if (!INTERNAL_SYSCALL_ERROR_P (val))
{
atomic_increment (&cmdp->cntr);
return 1;
}
else
return 0;
}
int
attribute_hidden
__nptl_setxid (struct xid_command *cmdp)
{
int signalled;
int result;
lll_lock (GL (dl_stack_cache_lock), LLL_PRIVATE);
xidcmd = cmdp;
cmdp->cntr = 0;
cmdp->error = -1;
struct pthread *self = THREAD_SELF;
/* Iterate over the list with system-allocated threads first. */
list_t *runp;
list_for_each (runp, &GL (dl_stack_used))
{
struct pthread *t = list_entry (runp, struct pthread, list);
if (t == self)
continue;
setxid_mark_thread (cmdp, t);
}
/* Now the list with threads using user-allocated stacks. */
list_for_each (runp, &GL (dl_stack_user))
{
struct pthread *t = list_entry (runp, struct pthread, list);
if (t == self)
continue;
setxid_mark_thread (cmdp, t);
}
/* Iterate until we don't succeed in signalling anyone. That means
we have gotten all running threads, and their children will be
automatically correct once started. */
do
{
signalled = 0;
list_for_each (runp, &GL (dl_stack_used))
{
struct pthread *t = list_entry (runp, struct pthread, list);
if (t == self)
continue;
signalled += setxid_signal_thread (cmdp, t);
}
list_for_each (runp, &GL (dl_stack_user))
{
struct pthread *t = list_entry (runp, struct pthread, list);
if (t == self)
continue;
signalled += setxid_signal_thread (cmdp, t);
}
int cur = cmdp->cntr;
while (cur != 0)
{
futex_wait_simple ((unsigned int *) &cmdp->cntr, cur,
FUTEX_PRIVATE);
cur = cmdp->cntr;
}
}
while (signalled != 0);
/* Clean up flags, so that no thread blocks during exit waiting
for a signal which will never come. */
list_for_each (runp, &GL (dl_stack_used))
{
struct pthread *t = list_entry (runp, struct pthread, list);
if (t == self)
continue;
setxid_unmark_thread (cmdp, t);
}
list_for_each (runp, &GL (dl_stack_user))
{
struct pthread *t = list_entry (runp, struct pthread, list);
if (t == self)
continue;
setxid_unmark_thread (cmdp, t);
}
/* This must be last, otherwise the current thread might not have
permissions to send SIGSETXID syscall to the other threads. */
result = INTERNAL_SYSCALL_NCS (cmdp->syscall_no, 3,
cmdp->id[0], cmdp->id[1], cmdp->id[2]);
int error = 0;
if (__glibc_unlikely (INTERNAL_SYSCALL_ERROR_P (result)))
{
error = INTERNAL_SYSCALL_ERRNO (result);
__set_errno (error);
result = -1;
}
setxid_error (cmdp, error);
lll_unlock (GL (dl_stack_cache_lock), LLL_PRIVATE);
return result;
}

4
nptl/pthreadP.h
View File

@ -701,8 +701,8 @@ extern void _pthread_cleanup_pop_restore (struct _pthread_cleanup_buffer *buffer
extern void __nptl_deallocate_tsd (void);
libc_hidden_proto (__nptl_deallocate_tsd)
extern void __nptl_setxid_error (struct xid_command *cmdp, int error)
attribute_hidden;
void __nptl_setxid_sighandler (int sig, siginfo_t *si, void *ctx);
libc_hidden_proto (__nptl_setxid_sighandler)
extern int __nptl_setxid (struct xid_command *cmdp) attribute_hidden;
extern void __nptl_stacks_freeres (void) attribute_hidden;

1
sysdeps/nptl/pthread-functions.h
View File

@ -30,7 +30,6 @@ struct xid_command;
the thread functions. */
struct pthread_functions
{
int (*ptr__nptl_setxid) (struct xid_command *);
};
/* Variable in libc.so. */

24
sysdeps/nptl/setxid.h
View File

@ -16,6 +16,7 @@
<https://www.gnu.org/licenses/>. */
#include <nptl/pthreadP.h>
#include <sys/single_threaded.h>
#include <sysdep.h>
#define __SETXID_1(cmd, arg1) \
@ -25,30 +26,10 @@
#define __SETXID_3(cmd, arg1, arg2, arg3) \
__SETXID_2 (cmd, arg1, arg2); cmd.id[2] = (long int) arg3
#ifdef SINGLE_THREAD
# define INLINE_SETXID_SYSCALL(name, nr, args...) \
INLINE_SYSCALL (name, nr, args)
#elif defined SHARED
#define INLINE_SETXID_SYSCALL(name, nr, args...) \
({ \
int __result; \
if (__builtin_expect (__libc_pthread_functions_init, 0)) \
{ \
struct xid_command __cmd; \
__cmd.syscall_no = __NR_##name; \
__SETXID_##nr (__cmd, args); \
__result = PTHFCT_CALL (ptr__nptl_setxid, (&__cmd)); \
} \
else \
__result = INLINE_SYSCALL (name, nr, args); \
__result; \
})
#else
# define INLINE_SETXID_SYSCALL(name, nr, args...) \
({ \
extern __typeof (__nptl_setxid) __nptl_setxid __attribute__((weak));\
int __result; \
if (__glibc_unlikely (__nptl_setxid != NULL)) \
if (!__libc_single_threaded) \
{ \
struct xid_command __cmd; \
__cmd.syscall_no = __NR_##name; \
@ -59,4 +40,3 @@
__result = INLINE_SYSCALL (name, nr, args); \
__result; \
})
#endif

4
sysdeps/unix/sysv/linux/internal-signals.h
View File

@ -110,8 +110,4 @@ __libc_signal_restore_set (const sigset_t *set)
INTERNAL_SYSCALL_CALL (rt_sigprocmask, SIG_SETMASK, set, NULL,
__NSIG_BYTES);
}
/* Used to communicate with signal handler. */
extern struct xid_command *__xidcmd attribute_hidden;
#endif