From 64d97d87611a39163aa121f17214f4a846954cee Mon Sep 17 00:00:00 2001 From: Mark Salyzyn Date: Mon, 9 Apr 2018 09:50:32 -0700 Subject: [PATCH] lmkd: limit capability set to minimum Set F() capability set and 'drop' lmkd from AID_ROOT to AID_LMKD uid and from AID_ROOT to AID_LMKD and AID_SYSTEM gid. /dev/memcg/memory.pressure defaults to root.root mode 0000, set it up as root.system mode 0040 to allow lmkd read access. Instrument failure to set SCHED_FIFO. Annotate access points that require elevated capabilities. Test: check /proc/`pidof lmkd`/status for capability set Test: lmkd_unit_test Bug: 77650566 Change-Id: I986081a0434cf6e842b63a55726380205b30a3ea --- .../include/private/android_filesystem_config.h | 1 + lmkd/lmkd.c | 17 ++++++++++++++--- lmkd/lmkd.rc | 4 +++- rootdir/init.rc | 3 +++ 4 files changed, 21 insertions(+), 4 deletions(-) diff --git a/libcutils/include/private/android_filesystem_config.h b/libcutils/include/private/android_filesystem_config.h index 5d17698de..8209167e3 100644 --- a/libcutils/include/private/android_filesystem_config.h +++ b/libcutils/include/private/android_filesystem_config.h @@ -129,6 +129,7 @@ #define AID_STATSD 1066 /* statsd daemon */ #define AID_INCIDENTD 1067 /* incidentd daemon */ #define AID_SECURE_ELEMENT 1068 /* secure element subsystem */ +#define AID_LMKD 1069 /* low memory killer daemon */ /* Changes to this file must be made in AOSP, *not* in internal branches. */ #define AID_SHELL 2000 /* adb and debug shell user */ diff --git a/lmkd/lmkd.c b/lmkd/lmkd.c index 151e1dc7b..80711bcfc 100644 --- a/lmkd/lmkd.c +++ b/lmkd/lmkd.c @@ -68,6 +68,7 @@ #define MEMINFO_PATH "/proc/meminfo" #define LINE_MAX 128 +/* gid containing AID_SYSTEM required */ #define INKERNEL_MINFREE_PATH "/sys/module/lowmemorykiller/parameters/minfree" #define INKERNEL_ADJ_PATH "/sys/module/lowmemorykiller/parameters/adj" @@ -455,6 +456,9 @@ static void cmd_procprio(LMKD_CTRL_PACKET packet) { return; } + /* gid containing AID_READPROC required */ + /* CAP_SYS_RESOURCE required */ + /* CAP_DAC_OVERRIDE required */ snprintf(path, sizeof(path), "/proc/%d/oom_score_adj", params.pid); snprintf(val, sizeof(val), "%d", params.oomadj); if (!writefilestring(path, val, false)) { @@ -496,8 +500,7 @@ static void cmd_procprio(LMKD_CTRL_PACKET packet) { soft_limit_mult = 64; } - snprintf(path, sizeof(path), - "/dev/memcg/apps/uid_%d/pid_%d/memory.soft_limit_in_bytes", + snprintf(path, sizeof(path), MEMCG_SYSFS_PATH "apps/uid_%d/pid_%d/memory.soft_limit_in_bytes", params.uid, params.pid); snprintf(val, sizeof(val), "%d", soft_limit_mult * EIGHT_MEGA); @@ -859,6 +862,7 @@ static int proc_get_size(int pid) { int total; ssize_t ret; + /* gid containing AID_READPROC required */ snprintf(path, PATH_MAX, "/proc/%d/statm", pid); fd = open(path, O_RDONLY | O_CLOEXEC); if (fd == -1) @@ -882,6 +886,7 @@ static char *proc_get_name(int pid) { char *cp; ssize_t ret; + /* gid containing AID_READPROC required */ snprintf(path, PATH_MAX, "/proc/%d/cmdline", pid); fd = open(path, O_RDONLY | O_CLOEXEC); if (fd == -1) @@ -949,6 +954,7 @@ static int kill_one_process(struct proc* procp, int min_score_adj, TRACE_KILL_START(pid); + /* CAP_KILL required */ r = kill(pid, SIGKILL); ALOGI( "Killing '%s' (%d), uid %d, adj %d\n" @@ -1267,6 +1273,7 @@ static bool init_mp_common(enum vmpressure_level level) { int level_idx = (int)level; const char *levelstr = level_name[level_idx]; + /* gid containing AID_SYSTEM required */ mpfd = open(MEMCG_SYSFS_PATH "memory.pressure_level", O_RDONLY | O_CLOEXEC); if (mpfd < 0) { ALOGI("No kernel memory.pressure_level support (errno=%d)", errno); @@ -1478,11 +1485,15 @@ int main(int argc __unused, char **argv __unused) { * pins ⊆ MCL_CURRENT, converging to just MCL_CURRENT as we fault * in pages. */ + /* CAP_IPC_LOCK required */ if (mlockall(MCL_CURRENT | MCL_FUTURE | MCL_ONFAULT) && (errno != EINVAL)) { ALOGW("mlockall failed %s", strerror(errno)); } - sched_setscheduler(0, SCHED_FIFO, ¶m); + /* CAP_NICE required */ + if (sched_setscheduler(0, SCHED_FIFO, ¶m)) { + ALOGW("set SCHED_FIFO failed %s", strerror(errno)); + } } mainloop(); diff --git a/lmkd/lmkd.rc b/lmkd/lmkd.rc index 3bb84abf6..76b60558a 100644 --- a/lmkd/lmkd.rc +++ b/lmkd/lmkd.rc @@ -1,6 +1,8 @@ service lmkd /system/bin/lmkd class core - group root readproc + user lmkd + group lmkd system readproc + capabilities DAC_OVERRIDE KILL IPC_LOCK SYS_NICE SYS_RESOURCE critical socket lmkd seqpacket 0660 system system writepid /dev/cpuset/system-background/tasks diff --git a/rootdir/init.rc b/rootdir/init.rc index 146257040..4f008acb6 100644 --- a/rootdir/init.rc +++ b/rootdir/init.rc @@ -34,6 +34,9 @@ on early-init # root memory control cgroup, used by lmkd mkdir /dev/memcg 0700 root system mount cgroup none /dev/memcg nodev noexec nosuid memory + # memory.pressure_level used by lmkd + chown root system /dev/memcg/memory.pressure_level + chmod 0040 /dev/memcg/memory.pressure_level # app mem cgroups, used by activity manager, lmkd and zygote mkdir /dev/memcg/apps/ 0755 system system # cgroup for system_server and surfaceflinger