Mark block device as read-only before mounting.
Mounting a block device as read-only still allows the filesystem to
write to the block device, while keeping the user-facing filesystem
interface "read-only". This behavior will make dm-verity to fail after
reboot if any block is modified during postinstall.
This patch marks the block device as read-only before mounting it, and
marks them read-only or read-write before using them during the update.
Bug: 27859604
TEST=Added logging and deployed an update to brillo, devices are marked RO/RW as needed during a delta update.
(cherry picked from commit 5fb356cac8a87c62fa83005d99370aa2f8416064)
Change-Id: I8797c35514e1f38c2a0395cedc8e1dce53e28350
diff --git a/common/utils.cc b/common/utils.cc
index 304aba2..5d15da0 100644
--- a/common/utils.cc
+++ b/common/utils.cc
@@ -641,6 +641,30 @@
return true;
}
+bool SetBlockDeviceReadOnly(const string& device, bool read_only) {
+ int fd = HANDLE_EINTR(open(device.c_str(), O_RDONLY | O_CLOEXEC));
+ if (fd < 0) {
+ PLOG(ERROR) << "Opening block device " << device;
+ return false;
+ }
+ ScopedFdCloser fd_closer(&fd);
+ // We take no action if not needed.
+ int read_only_flag;
+ int expected_flag = read_only ? 1 : 0;
+ int rc = ioctl(fd, BLKROGET, &read_only_flag);
+ // In case of failure reading the setting we will try to set it anyway.
+ if (rc == 0 && read_only_flag == expected_flag)
+ return true;
+
+ rc = ioctl(fd, BLKROSET, &expected_flag);
+ if (rc != 0) {
+ PLOG(ERROR) << "Marking block device " << device << " as read_only="
+ << expected_flag;
+ return false;
+ }
+ return true;
+}
+
bool MountFilesystem(const string& device,
const string& mountpoint,
unsigned long mountflags, // NOLINT(runtime/int)
diff --git a/common/utils.h b/common/utils.h
index 686f117..88c33b7 100644
--- a/common/utils.h
+++ b/common/utils.h
@@ -178,6 +178,10 @@
// /dev/sda3. Return empty string on error.
std::string MakePartitionNameForMount(const std::string& part_name);
+// Set the read-only attribute on the block device |device| to the value passed
+// in |read_only|. Return whether the operation succeeded.
+bool SetBlockDeviceReadOnly(const std::string& device, bool read_only);
+
// Synchronously mount or unmount a filesystem. Return true on success.
// When mounting, it will attempt to mount the device as the passed filesystem
// type |type|, with the passed |flags| options. If |type| is empty, "ext2",