diff --git a/libcutils/ashmem-dev.c b/libcutils/ashmem-dev.c index a5203e13f..77e4d0d97 100644 --- a/libcutils/ashmem-dev.c +++ b/libcutils/ashmem-dev.c @@ -22,6 +22,7 @@ #include #include +#include #include #include #include @@ -34,6 +35,89 @@ #define ASHMEM_DEVICE "/dev/ashmem" +/* ashmem identity */ +static dev_t __ashmem_rdev; +/* + * If we trigger a signal handler in the middle of locked activity and the + * signal handler calls ashmem, we could get into a deadlock state. + */ +static pthread_mutex_t __ashmem_lock = PTHREAD_MUTEX_INITIALIZER; + +/* logistics of getting file descriptor for ashmem */ +static int __ashmem_open_locked() +{ + int ret; + struct stat st; + + int fd = TEMP_FAILURE_RETRY(open(ASHMEM_DEVICE, O_RDWR)); + if (fd < 0) { + return fd; + } + + ret = TEMP_FAILURE_RETRY(fstat(fd, &st)); + if (ret < 0) { + int save_errno = errno; + close(fd); + errno = save_errno; + return ret; + } + if (!S_ISCHR(st.st_mode) || !st.st_rdev) { + close(fd); + errno = ENOTTY; + return -1; + } + + __ashmem_rdev = st.st_rdev; + return fd; +} + +static int __ashmem_open() +{ + int fd; + + pthread_mutex_lock(&__ashmem_lock); + fd = __ashmem_open_locked(); + pthread_mutex_unlock(&__ashmem_lock); + + return fd; +} + +/* Make sure file descriptor references ashmem, negative number means false */ +static int __ashmem_is_ashmem(int fd) +{ + dev_t rdev; + struct stat st; + + if (TEMP_FAILURE_RETRY(fstat(fd, &st)) < 0) { + return -1; + } + + if (S_ISCHR(st.st_mode) && st.st_rdev) { + pthread_mutex_lock(&__ashmem_lock); + rdev = __ashmem_rdev; + if (rdev) { + pthread_mutex_unlock(&__ashmem_lock); + } else { + int fd = __ashmem_open_locked(); + if (fd < 0) { + pthread_mutex_unlock(&__ashmem_lock); + return -1; + } + rdev = __ashmem_rdev; + pthread_mutex_unlock(&__ashmem_lock); + + close(fd); + } + + if (st.st_rdev == rdev) { + return 0; + } + } + + errno = ENOTTY; + return -1; +} + /* * ashmem_create_region - creates a new ashmem region and returns the file * descriptor, or <0 on error @@ -45,7 +129,7 @@ int ashmem_create_region(const char *name, size_t size) { int ret, save_errno; - int fd = TEMP_FAILURE_RETRY(open(ASHMEM_DEVICE, O_RDWR)); + int fd = __ashmem_open(); if (fd < 0) { return fd; } @@ -76,22 +160,44 @@ error: int ashmem_set_prot_region(int fd, int prot) { + int ret = __ashmem_is_ashmem(fd); + if (ret < 0) { + return ret; + } + return TEMP_FAILURE_RETRY(ioctl(fd, ASHMEM_SET_PROT_MASK, prot)); } int ashmem_pin_region(int fd, size_t offset, size_t len) { struct ashmem_pin pin = { offset, len }; + + int ret = __ashmem_is_ashmem(fd); + if (ret < 0) { + return ret; + } + return TEMP_FAILURE_RETRY(ioctl(fd, ASHMEM_PIN, &pin)); } int ashmem_unpin_region(int fd, size_t offset, size_t len) { struct ashmem_pin pin = { offset, len }; + + int ret = __ashmem_is_ashmem(fd); + if (ret < 0) { + return ret; + } + return TEMP_FAILURE_RETRY(ioctl(fd, ASHMEM_UNPIN, &pin)); } int ashmem_get_size_region(int fd) { + int ret = __ashmem_is_ashmem(fd); + if (ret < 0) { + return ret; + } + return TEMP_FAILURE_RETRY(ioctl(fd, ASHMEM_GET_SIZE, NULL)); }