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Allow update_engine to scan /sys/fs and /sys/fs/f2fs.

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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
This commit is contained in:
David Anderson 2021-04-07 21:51:33 -07:00
parent 10c2ed4e47
commit 5a0d5ccdf7
1 changed files with 4 additions and 0 deletions
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4
public/update_engine_common.te
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@ -59,6 +59,10 @@ r_dir_file(update_engine_common, sysfs_dt_firmware_android)
# 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;