There are some ROMs based on AOSP that calls on second stage init
with argc: 2 but with first_arg: "". This causes KSU to not work
properly on those systems.
Signed-off-by: Edrick Sinsuan <evcsinsuan@gmail.com>
When kernel is compiled with CONFIG_DEBUG_ATOMIC_SLEEP enabled, it
prints the following splat in dmesg during post boot:
[ 6.739169] init: Opening SELinux policy
[ 6.751520] init: Loading SELinux policy
[ 6.894684] SELinux: policy capability network_peer_controls=1 [
6.894688] SELinux: policy capability open_perms=1 [ 6.894690] SELinux:
policy capability extended_socket_class=1 [ 6.894691] SELinux: policy
capability always_check_network=0 [ 6.894693] SELinux: policy capability
cgroup_seclabel=0 [ 6.894695] SELinux: policy capability
nnp_nosuid_transition=1 [ 7.214323] selinux: SELinux: Loaded file
context from: [ 7.214332] selinux:
/system/etc/selinux/plat_file_contexts [ 7.214339] selinux:
/system_ext/etc/selinux/system_ext_file_contexts [ 7.214345] selinux:
/product/etc/selinux/product_file_contexts [ 7.214350] selinux:
/vendor/etc/selinux/vendor_file_contexts [ 7.214356] selinux:
/odm/etc/selinux/odm_file_contexts [ 7.216398] KernelSU:
/system/bin/init argc: 2
[ 7.216401] KernelSU: /system/bin/init first arg: second_stage [
7.216403] KernelSU: /system/bin/init second_stage executed [ 7.216506]
BUG: sleeping function called from invalid context at
security/selinux/ss/hashtab.c:47 [ 7.216512] in_atomic(): 0,
irqs_disabled(): 0, non_block: 0, pid: 1, name: init [ 7.216516]
preempt_count: 0, expected: 0
[ 7.216518] RCU nest depth: 1, expected: 0
[ 7.216524] CPU: 6 PID: 1 Comm: init Not tainted
5.4.289-Scarlet-v2.0-beta3 #1 [ 7.216526] Hardware name: redwood based
Qualcomm Technologies, Inc. SM7325 (DT) [ 7.216528] Call trace:
[ 7.216536] dump_backtrace+0x0/0x210
[ 7.216539] show_stack+0x14/0x20
[ 7.216544] dump_stack+0x9c/0xec
[ 7.216548] __might_resched+0x1f0/0x210
[ 7.216552] hashtab_insert+0x38/0x230
[ 7.216557] add_type+0xd4/0x2e0
[ 7.216559] ksu_type+0x24/0x60
[ 7.216562] apply_kernelsu_rules+0xa8/0x650
[ 7.216565] ksu_handle_execveat_ksud+0x2a8/0x460
[ 7.216568] ksu_handle_execveat+0x2c/0x60
[ 7.216571] __arm64_sys_execve+0xe8/0xf0
[ 7.216574] el0_svc_common+0xf4/0x1a0
[ 7.216577] do_el0_svc+0x2c/0x40
[ 7.216579] el0_sync_handler+0x18c/0x200
[ 7.216582] el0_sync+0x140/0x180
This is because apply_kernelsu_rules() uses rcu_read_lock() to protect
SELinux policy modifications. However, cond_resched() from
hashtab_insert() at security/selinux/ss/hashtab.c is internally called
and it sleeps which is illegal under an RCU read-side critical section.
While replacing it with a spinlock would suppress the warning, this is
fundamentally incorrect because sleeping is illegal while holding a
spinlock and spinlock would turn off preemption which isn't an ideal
solution since it intentionally turns off rescheduling, and can lead to
deadlocks.
Instead, replace the RCU lock with a mutex lock. Mutex lock allows
sleeping when necessary, which is appropriate here because
apply_kernelsu_rules() runs in process context, not in atomic or
interrupt context. As apply_kernelsu_rules() is invoked only once during
post boot (SYSTEM_RUNNING), the mutex lock does not introduce any major
runtime performance regression and provides correct synchronization.
Fixes: https://github.com/tiann/KernelSU/issues/2637
Signed-off-by: Tashfin Shakeer Rhythm <tashfinshakeerrhythm@gmail.com>
Rifat Azad