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protect sem_open against cancellation

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also fix one minor bug: failure to free the early-reserved slot when
the semaphore later found to already be mapped.
This commit is contained in:
Rich Felker 2012-09-30 19:44:45 -04:00
parent bf258341b7
commit e44849f5cf
1 changed files with 19 additions and 13 deletions
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32
src/thread/sem_open.c
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@ -29,7 +29,7 @@ sem_t *sem_open(const char *name, int flags, ...)
va_list ap;
mode_t mode;
unsigned value;
int fd, i, e, slot, first=1, cnt;
int fd, i, e, slot, first=1, cnt, cs;
sem_t newsem;
void *map;
char tmp[64];
@ -74,6 +74,8 @@ sem_t *sem_open(const char *name, int flags, ...)
return SEM_FAILED;
}
pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &cs);
for (;;) {
/* If exclusive mode is not requested, try opening an
* existing file first and fall back to creation. */
@ -83,16 +85,16 @@ sem_t *sem_open(const char *name, int flags, ...)
if ((map = mmap(0, sizeof(sem_t), PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0)) == MAP_FAILED ||
fstat(fd, &st) < 0) {
close(fd);
return SEM_FAILED;
goto fail;
}
close(fd);
break;
}
if (errno != ENOENT)
return SEM_FAILED;
goto fail;
}
if (!(flags & O_CREAT))
return SEM_FAILED;
goto fail;
if (first) {
first = 0;
va_start(ap, flags);
@ -101,7 +103,7 @@ sem_t *sem_open(const char *name, int flags, ...)
va_end(ap);
if (value > SEM_VALUE_MAX) {
errno = EINVAL;
return SEM_FAILED;
goto fail;
}
sem_init(&newsem, 1, value);
}
@ -112,13 +114,13 @@ sem_t *sem_open(const char *name, int flags, ...)
fd = open(tmp, O_CREAT|O_EXCL|FLAGS, mode);
if (fd < 0) {
if (errno == EEXIST) continue;
return SEM_FAILED;
goto fail;
}
if (write(fd, &newsem, sizeof newsem) != sizeof newsem || fstat(fd, &st) < 0 ||
(map = mmap(0, sizeof(sem_t), PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0)) == MAP_FAILED) {
close(fd);
unlink(tmp);
return SEM_FAILED;
goto fail;
}
close(fd);
if (link(tmp, name) == 0) break;
@ -128,7 +130,7 @@ sem_t *sem_open(const char *name, int flags, ...)
* otherwise, next iteration will try to open the
* existing file. */
if (e != EEXIST || flags == (O_CREAT|O_EXCL))
return SEM_FAILED;
goto fail;
}
/* See if the newly mapped semaphore is already mapped. If
@ -138,16 +140,20 @@ sem_t *sem_open(const char *name, int flags, ...)
for (i=0; i<SEM_NSEMS_MAX && semtab[i].ino != st.st_ino; i++);
if (i<SEM_NSEMS_MAX) {
munmap(map, sizeof(sem_t));
semtab[i].refcnt++;
UNLOCK(lock);
return semtab[i].sem;
semtab[slot].sem = 0;
slot = i;
map = semtab[i].sem;
}
semtab[slot].refcnt = 1;
semtab[slot].refcnt++;
semtab[slot].sem = map;
semtab[slot].ino = st.st_ino;
UNLOCK(lock);
pthread_setcancelstate(cs, 0);
return map;
fail:
pthread_setcancelstate(cs, 0);
return SEM_FAILED;
}
int sem_close(sem_t *sem)