restrict access to timing information in /proc
These APIs expose sensitive information via timing side channels. This
leaves access via the adb shell intact along with the current uses by
dumpstate, init and system_server.
The /proc/interrupts and /proc/stat files were covered in this paper:
https://www.lightbluetouchpaper.org/2016/07/29/yet-another-android-side-channel/
The /proc/softirqs, /proc/timer_list and /proc/timer_stats files are
also relevant.
Access to /proc has been greatly restricted since then, with untrusted
apps no longer having direct access to these, but stricter restrictions
beyond that would be quite useful.
Change-Id: Ibed16674856569d26517e5729f0f194b830cfedd
diff --git a/dumpstate.te b/dumpstate.te
index 4a475d1..08dcb4d 100644
--- a/dumpstate.te
+++ b/dumpstate.te
@@ -142,3 +142,5 @@
allow dumpstate debugfs_tracing:file rw_file_perms;
allow dumpstate debugfs_trace_marker:file getattr;
allow dumpstate atrace_exec:file rx_file_perms;
+
+allow dumpstate proc_interrupts:file r_file_perms;
diff --git a/file.te b/file.te
index 7b6b4a9..628c237 100644
--- a/file.te
+++ b/file.te
@@ -13,10 +13,13 @@
type qtaguid_proc, fs_type, mlstrustedobject;
type proc_bluetooth_writable, fs_type;
type proc_cpuinfo, fs_type;
+type proc_interrupts, fs_type;
type proc_iomem, fs_type;
type proc_meminfo, fs_type;
type proc_net, fs_type;
+type proc_stat, fs_type;
type proc_sysrq, fs_type;
+type proc_timer, fs_type;
type proc_uid_cputime_showstat, fs_type;
type proc_uid_cputime_removeuid, fs_type;
type selinuxfs, fs_type, mlstrustedobject;
diff --git a/genfs_contexts b/genfs_contexts
index 81749fd..57b967c 100644
--- a/genfs_contexts
+++ b/genfs_contexts
@@ -2,11 +2,14 @@
genfscon rootfs / u:object_r:rootfs:s0
# proc labeling can be further refined (longest matching prefix).
genfscon proc / u:object_r:proc:s0
+genfscon proc /interrupts u:object_r:proc_interrupts:s0
genfscon proc /iomem u:object_r:proc_iomem:s0
genfscon proc /meminfo u:object_r:proc_meminfo:s0
genfscon proc /net u:object_r:proc_net:s0
genfscon proc /net/xt_qtaguid/ctrl u:object_r:qtaguid_proc:s0
genfscon proc /cpuinfo u:object_r:proc_cpuinfo:s0
+genfscon proc /softirqs u:object_r:proc_timer:s0
+genfscon proc /stat u:object_r:proc_stat:s0
genfscon proc /sysrq-trigger u:object_r:proc_sysrq:s0
genfscon proc /sys/fs/protected_hardlinks u:object_r:proc_security:s0
genfscon proc /sys/fs/protected_symlinks u:object_r:proc_security:s0
@@ -24,6 +27,8 @@
genfscon proc /sys/vm/mmap_min_addr u:object_r:proc_security:s0
genfscon proc /sys/vm/drop_caches u:object_r:proc_drop_caches:s0
genfscon proc /sys/vm/overcommit_memory u:object_r:proc_overcommit_memory:s0
+genfscon proc /timer_list u:object_r:proc_timer:s0
+genfscon proc /timer_stats u:object_r:proc_timer:s0
genfscon proc /uid_cputime/show_uid_stat u:object_r:proc_uid_cputime_showstat:s0
genfscon proc /uid_cputime/remove_uid_range u:object_r:proc_uid_cputime_removeuid:s0
diff --git a/init.te b/init.te
index 8895985..ff029ab 100644
--- a/init.te
+++ b/init.te
@@ -198,6 +198,9 @@
# Write to /proc/sysrq-trigger.
allow init proc_sysrq:file w_file_perms;
+# Read /proc/stat for bootchart.
+allow init proc_stat:file r_file_perms;
+
# Reboot.
allow init self:capability sys_boot;
diff --git a/shell.te b/shell.te
index c263f0c..afa4c91 100644
--- a/shell.te
+++ b/shell.te
@@ -89,7 +89,10 @@
# allow shell to look through /proc/ for ps, top, netstat
r_dir_file(shell, proc)
r_dir_file(shell, proc_net)
+allow shell proc_interrupts:file r_file_perms;
allow shell proc_meminfo:file r_file_perms;
+allow shell proc_stat:file r_file_perms;
+allow shell proc_timer:file r_file_perms;
r_dir_file(shell, cgroup)
allow shell domain:dir { search open read getattr };
allow shell domain:{ file lnk_file } { open read getattr };
diff --git a/system_server.te b/system_server.te
index 3bf6e4e..cb06d6d 100644
--- a/system_server.te
+++ b/system_server.te
@@ -101,6 +101,9 @@
# Write to /proc/sysrq-trigger.
allow system_server proc_sysrq:file rw_file_perms;
+# Read /proc/stat for CPU usage statistics
+allow system_server proc_stat:file r_file_perms;
+
# Read /sys/kernel/debug/wakeup_sources.
allow system_server debugfs:file r_file_perms;