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authorRich Felker <dalias@aerifal.cx>2011-03-24 14:18:00 -0400
committerRich Felker <dalias@aerifal.cx>2011-03-24 14:18:00 -0400
commitb470030f839a375e5030ec9d44903ef7581c15a2 (patch)
tree462b1df89a3ea45bcf50b9d0a844472576ed6585
parent095820016689dfdc9141f477a86de22054c86078 (diff)
downloadmusl-b470030f839a375e5030ec9d44903ef7581c15a2.tar.gz
overhaul cancellation to fix resource leaks and dangerous behavior with signals
this commit addresses two issues: 1. a race condition, whereby a cancellation request occurring after a syscall returned from kernelspace but before the subsequent CANCELPT_END would cause cancellable resource-allocating syscalls (like open) to leak resources. 2. signal handlers invoked while the thread was blocked at a cancellation point behaved as if asynchronous cancellation mode wer in effect, resulting in potentially dangerous state corruption if a cancellation request occurs. the glibc/nptl implementation of threads shares both of these issues. with this commit, both are fixed. however, cancellation points encountered in a signal handler will not be acted upon if the signal was received while the thread was already at a cancellation point. they will of course be acted upon after the signal handler returns, so in real-world usage where signal handlers quickly return, it should not be a problem. it's possible to solve this problem too by having sigaction() wrap all signal handlers with a function that uses a pthread_cleanup handler to catch cancellation, patch up the saved context, and return into the cancellable function that will catch and act upon the cancellation. however that would be a lot of complexity for minimal if any benefit...
-rw-r--r--arch/i386/pthread_arch.h3
-rw-r--r--arch/x86_64/pthread_arch.h3
-rw-r--r--src/internal/libc.h3
-rw-r--r--src/process/waitid.c8
-rw-r--r--src/process/waitpid.c8
-rw-r--r--src/select/pselect.c1
-rw-r--r--src/select/select.c1
-rw-r--r--src/signal/sigsuspend.c1
-rw-r--r--src/signal/sigtimedwait.c1
-rw-r--r--src/termios/tcdrain.c1
-rw-r--r--src/thread/pthread_cond_timedwait.c10
-rw-r--r--src/thread/pthread_create.c16
-rw-r--r--src/thread/sem_timedwait.c5
-rw-r--r--src/time/nanosleep.c1
14 files changed, 49 insertions, 13 deletions
diff --git a/arch/i386/pthread_arch.h b/arch/i386/pthread_arch.h
index 155b4847..64d75cbc 100644
--- a/arch/i386/pthread_arch.h
+++ b/arch/i386/pthread_arch.h
@@ -4,3 +4,6 @@ static inline struct pthread *__pthread_self()
__asm__ ("movl %%gs:0,%0" : "=r" (self) );
return self;
}
+
+#define PC_AT_SYS(c) \
+ (*(uint16_t *)(((ucontext_t *)(c))->uc_mcontext.__gregs[14])==0x80cd)
diff --git a/arch/x86_64/pthread_arch.h b/arch/x86_64/pthread_arch.h
index 40d26797..af7ae86e 100644
--- a/arch/x86_64/pthread_arch.h
+++ b/arch/x86_64/pthread_arch.h
@@ -4,3 +4,6 @@ static inline struct pthread *__pthread_self()
__asm__ ("movq %%fs:0,%0" : "=r" (self) );
return self;
}
+
+#define PC_AT_SYS(c) \
+ (*(uint16_t *)(((ucontext_t *)(c))->uc_mcontext.__gregs[16])==0x050f)
diff --git a/src/internal/libc.h b/src/internal/libc.h
index 3d09bf6a..bbbb3a4c 100644
--- a/src/internal/libc.h
+++ b/src/internal/libc.h
@@ -44,7 +44,8 @@ void __lockfile(FILE *);
#define UNLOCK(x) (*(x)=0)
#define CANCELPT(x) (libc.cancelpt ? libc.cancelpt((x)),0 : (void)(x),0)
#define CANCELPT_BEGIN CANCELPT(1)
-#define CANCELPT_END CANCELPT(0)
+#define CANCELPT_TRY CANCELPT(0)
+#define CANCELPT_END CANCELPT(-1)
extern char **__environ;
#define environ __environ
diff --git a/src/process/waitid.c b/src/process/waitid.c
index b1e5e9b1..4fa7c024 100644
--- a/src/process/waitid.c
+++ b/src/process/waitid.c
@@ -1,7 +1,13 @@
#include <sys/wait.h>
#include "syscall.h"
+#include "libc.h"
int waitid(idtype_t type, id_t id, siginfo_t *info, int options)
{
- return syscall(SYS_waitid, type, id, info, options, 0);
+ int r;
+ CANCELPT_BEGIN;
+ r = syscall(SYS_waitid, type, id, info, options, 0);
+ if (r<0) CANCELPT_TRY;
+ CANCELPT_END;
+ return r;
}
diff --git a/src/process/waitpid.c b/src/process/waitpid.c
index ec2757b3..5e0320f7 100644
--- a/src/process/waitpid.c
+++ b/src/process/waitpid.c
@@ -1,7 +1,13 @@
#include <sys/wait.h>
#include "syscall.h"
+#include "libc.h"
pid_t waitpid(pid_t pid, int *status, int options)
{
- return syscall(SYS_wait4, pid, status, options, 0);
+ int r;
+ CANCELPT_BEGIN;
+ r = syscall(SYS_wait4, pid, status, options, 0);
+ if (r<0) CANCELPT_TRY;
+ CANCELPT_END;
+ return r;
}
diff --git a/src/select/pselect.c b/src/select/pselect.c
index 63ea0695..155a6eb0 100644
--- a/src/select/pselect.c
+++ b/src/select/pselect.c
@@ -10,6 +10,7 @@ int pselect(int n, fd_set *rfds, fd_set *wfds, fd_set *efds, const struct timesp
if (ts) ts_tmp = *ts;
CANCELPT_BEGIN;
r = syscall(SYS_pselect6, n, rfds, wfds, efds, ts ? &ts_tmp : 0, data);
+ CANCELPT_TRY;
CANCELPT_END;
return r;
}
diff --git a/src/select/select.c b/src/select/select.c
index 12322718..b38e7fd2 100644
--- a/src/select/select.c
+++ b/src/select/select.c
@@ -7,6 +7,7 @@ int select(int n, fd_set *rfds, fd_set *wfds, fd_set *efds, struct timeval *tv)
int r;
CANCELPT_BEGIN;
r = syscall(SYS_select, n, rfds, wfds, efds, tv);
+ CANCELPT_TRY;
CANCELPT_END;
return r;
}
diff --git a/src/signal/sigsuspend.c b/src/signal/sigsuspend.c
index 6c13fce1..9ee71240 100644
--- a/src/signal/sigsuspend.c
+++ b/src/signal/sigsuspend.c
@@ -7,6 +7,7 @@ int sigsuspend(const sigset_t *mask)
int ret;
CANCELPT_BEGIN;
ret = syscall(__NR_rt_sigsuspend, mask, 8);
+ if (ret<0) CANCELPT_TRY;
CANCELPT_END;
return ret;
}
diff --git a/src/signal/sigtimedwait.c b/src/signal/sigtimedwait.c
index a0edaaf3..86a2c879 100644
--- a/src/signal/sigtimedwait.c
+++ b/src/signal/sigtimedwait.c
@@ -9,6 +9,7 @@ int sigtimedwait(const sigset_t *mask, siginfo_t *si, const struct timespec *tim
CANCELPT_BEGIN;
do {
ret = syscall(__NR_rt_sigtimedwait, mask, si, timeout, 8);
+ if (ret<0) CANCELPT_TRY;
} while (ret<0 && errno==EINTR);
CANCELPT_END;
return ret;
diff --git a/src/termios/tcdrain.c b/src/termios/tcdrain.c
index 8e889b51..9ff1ecd5 100644
--- a/src/termios/tcdrain.c
+++ b/src/termios/tcdrain.c
@@ -7,6 +7,7 @@ int tcdrain(int fd)
int ret;
CANCELPT_BEGIN;
ret = ioctl(fd, TCSBRK, 1);
+ CANCELPT_TRY;
CANCELPT_END;
return ret;
}
diff --git a/src/thread/pthread_cond_timedwait.c b/src/thread/pthread_cond_timedwait.c
index 228f61f7..1439aace 100644
--- a/src/thread/pthread_cond_timedwait.c
+++ b/src/thread/pthread_cond_timedwait.c
@@ -8,19 +8,21 @@ static void relock(void *m)
int pthread_cond_timedwait(pthread_cond_t *c, pthread_mutex_t *m, const struct timespec *ts)
{
int r, e=0;
- CANCELPT(0);
+ CANCELPT_BEGIN;
+ CANCELPT_END;
pthread_cleanup_push(relock, m);
c->_c_block = 1;
if ((r=pthread_mutex_unlock(m))) return r;
- CANCELPT(1);
+ CANCELPT_BEGIN;
e = __timedwait(&c->_c_block, 1, c->_c_clock, ts, 0);
- CANCELPT(0);
+ CANCELPT_END;
pthread_cleanup_pop(0);
if ((r=pthread_mutex_lock(m))) return r;
- CANCELPT(0);
+ CANCELPT_BEGIN;
+ CANCELPT_END;
return e;
}
diff --git a/src/thread/pthread_create.c b/src/thread/pthread_create.c
index 17a47f6a..785a82b8 100644
--- a/src/thread/pthread_create.c
+++ b/src/thread/pthread_create.c
@@ -42,6 +42,12 @@ void __pthread_unwind_next(struct __ptcb *cb)
static void docancel(struct pthread *self)
{
struct __ptcb cb = { .__next = self->cancelbuf };
+ sigset_t set;
+ self->canceldisable = 1;
+ self->cancelasync = 0;
+ sigemptyset(&set);
+ sigaddset(&set, SIGCANCEL);
+ __libc_sigprocmask(SIG_UNBLOCK, &set, 0);
__pthread_unwind_next(&cb);
}
@@ -50,17 +56,17 @@ static void cancel_handler(int sig, siginfo_t *si, void *ctx)
struct pthread *self = __pthread_self();
if (si->si_code > 0 || si->si_pid != self->pid) return;
self->cancel = 1;
- if (self->canceldisable || (!self->cancelasync && !self->cancelpoint))
- return;
- docancel(self);
+ if (self->canceldisable) return;
+ if (self->cancelasync || (self->cancelpoint==1 && PC_AT_SYS(ctx)))
+ docancel(self);
}
static void cancelpt(int x)
{
struct pthread *self = __pthread_self();
if (self->canceldisable) return;
- self->cancelpoint = x;
- if (self->cancel) docancel(self);
+ if ((self->cancelpoint+=x)==1 && x>=0 && self->cancel)
+ docancel(self);
}
/* "rsyscall" is a mechanism by which a thread can synchronously force all
diff --git a/src/thread/sem_timedwait.c b/src/thread/sem_timedwait.c
index ad3bf075..11a01700 100644
--- a/src/thread/sem_timedwait.c
+++ b/src/thread/sem_timedwait.c
@@ -9,15 +9,18 @@ int sem_timedwait(sem_t *sem, const struct timespec *at)
if (a_fetch_add(sem->__val, -1) > 0) return 0;
val = a_fetch_add(sem->__val, 1)+1;
if (val==1) __wake(sem->__val, 1, 0);
- CANCELPT_BEGIN;
if (at && at->tv_nsec >= 1000000000UL) {
errno = EINVAL;
return -1;
}
+ CANCELPT_BEGIN;
if (val <= 0 && __timedwait(sem->__val, val, CLOCK_REALTIME, at, 0) == ETIMEDOUT) {
errno = ETIMEDOUT;
+ CANCELPT_TRY;
+ CANCELPT_END;
return -1;
}
+ CANCELPT_TRY;
CANCELPT_END;
}
}
diff --git a/src/time/nanosleep.c b/src/time/nanosleep.c
index 2f65762f..0e0753f3 100644
--- a/src/time/nanosleep.c
+++ b/src/time/nanosleep.c
@@ -8,6 +8,7 @@ int nanosleep(const struct timespec *req, struct timespec *rem)
int ret;
CANCELPT_BEGIN;
ret = syscall(SYS_nanosleep, req, rem);
+ CANCELPT_TRY;
CANCELPT_END;
return ret;
}