Allow update_engine to scan /sys/fs and /sys/fs/f2fs.
When a bug causes us to leak a file descriptor or resource in the OTA
path, it can cause unremovable device-mapper devices. The companion CL
in this topic attempts to diagnose such problems by performing a quick
scan for things depending on an unremovable block device: mounts, loop
devices, and other device-mapper nodes.
To detect mounts it would normally be enough to scan /proc/mounts, but
with MNT_DETACH the filesystem may still be mounted but not visible to
update_engine. This is exactly what happened in b/184715543.
To scan for such cases, we look for /sys/fs/ext4/<name> or
/sys/fs/f2fs/<name> where <name> is the block device. To make this work,
we grant update_engine r_dir_perms to sysfs and sysfs_f2fs_dir. It
doesn't actually need to read the contents of any files, the presence of
the inode is good enough.
Bug: N/A
Test: manual test
Change-Id: Ib085c9c814180b360e2170135011261bbb7e35b6
diff --git a/public/update_engine_common.te b/public/update_engine_common.te
index 286ff4d..e8fd29e 100644
--- a/public/update_engine_common.te
+++ b/public/update_engine_common.te
@@ -59,6 +59,10 @@
# Needed because libdm reads sysfs to validate when a dm path is ready.
r_dir_file(update_engine_common, sysfs_dm)
+# Scan files in /sys/fs/ext4 and /sys/fs/f2fs for device-mapper diagnostics.
+allow update_engine_common sysfs:dir r_dir_perms;
+allow update_engine_common sysfs_fs_f2fs:dir r_dir_perms;
+
# read / write on /dev/device-mapper to map / unmap devices
allow update_engine_common dm_device:chr_file rw_file_perms;