kernel_optimize_test/kernel/ucount.c
Nikolay Borisov 880a38547f userns: Make ucounts lock irq-safe
The ucounts_lock is being used to protect various ucounts lifecycle
management functionalities. However, those services can also be invoked
when a pidns is being freed in an RCU callback (e.g. softirq context).
This can lead to deadlocks. There were already efforts trying to
prevent similar deadlocks in add7c65ca4 ("pid: fix lockdep deadlock
warning due to ucount_lock"), however they just moved the context
from hardirq to softrq. Fix this issue once and for all by explictly
making the lock disable irqs altogether.

Dmitry Vyukov <dvyukov@google.com> reported:

> I've got the following deadlock report while running syzkaller fuzzer
> on eec0d3d065bfcdf9cd5f56dd2a36b94d12d32297 of linux-next (on odroid
> device if it matters):
>
> =================================
> [ INFO: inconsistent lock state ]
> 4.10.0-rc3-next-20170112-xc2-dirty #6 Not tainted
> ---------------------------------
> inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W} usage.
> swapper/2/0 [HC0[0]:SC1[1]:HE1:SE0] takes:
>  (ucounts_lock){+.?...}, at: [<     inline     >] spin_lock
> ./include/linux/spinlock.h:302
>  (ucounts_lock){+.?...}, at: [<ffff2000081678c8>]
> put_ucounts+0x60/0x138 kernel/ucount.c:162
> {SOFTIRQ-ON-W} state was registered at:
> [<ffff2000081c82d8>] mark_lock+0x220/0xb60 kernel/locking/lockdep.c:3054
> [<     inline     >] mark_irqflags kernel/locking/lockdep.c:2941
> [<ffff2000081c97a8>] __lock_acquire+0x388/0x3260 kernel/locking/lockdep.c:3295
> [<ffff2000081cce24>] lock_acquire+0xa4/0x138 kernel/locking/lockdep.c:3753
> [<     inline     >] __raw_spin_lock ./include/linux/spinlock_api_smp.h:144
> [<ffff200009798128>] _raw_spin_lock+0x90/0xd0 kernel/locking/spinlock.c:151
> [<     inline     >] spin_lock ./include/linux/spinlock.h:302
> [<     inline     >] get_ucounts kernel/ucount.c:131
> [<ffff200008167c28>] inc_ucount+0x80/0x6c8 kernel/ucount.c:189
> [<     inline     >] inc_mnt_namespaces fs/namespace.c:2818
> [<ffff200008481850>] alloc_mnt_ns+0x78/0x3a8 fs/namespace.c:2849
> [<ffff200008487298>] create_mnt_ns+0x28/0x200 fs/namespace.c:2959
> [<     inline     >] init_mount_tree fs/namespace.c:3199
> [<ffff200009bd6674>] mnt_init+0x258/0x384 fs/namespace.c:3251
> [<ffff200009bd60bc>] vfs_caches_init+0x6c/0x80 fs/dcache.c:3626
> [<ffff200009bb1114>] start_kernel+0x414/0x460 init/main.c:648
> [<ffff200009bb01e8>] __primary_switched+0x6c/0x70 arch/arm64/kernel/head.S:456
> irq event stamp: 2316924
> hardirqs last  enabled at (2316924): [<     inline     >] rcu_do_batch
> kernel/rcu/tree.c:2911
> hardirqs last  enabled at (2316924): [<     inline     >]
> invoke_rcu_callbacks kernel/rcu/tree.c:3182
> hardirqs last  enabled at (2316924): [<     inline     >]
> __rcu_process_callbacks kernel/rcu/tree.c:3149
> hardirqs last  enabled at (2316924): [<ffff200008210414>]
> rcu_process_callbacks+0x7a4/0xc28 kernel/rcu/tree.c:3166
> hardirqs last disabled at (2316923): [<     inline     >] rcu_do_batch
> kernel/rcu/tree.c:2900
> hardirqs last disabled at (2316923): [<     inline     >]
> invoke_rcu_callbacks kernel/rcu/tree.c:3182
> hardirqs last disabled at (2316923): [<     inline     >]
> __rcu_process_callbacks kernel/rcu/tree.c:3149
> hardirqs last disabled at (2316923): [<ffff20000820fe80>]
> rcu_process_callbacks+0x210/0xc28 kernel/rcu/tree.c:3166
> softirqs last  enabled at (2316912): [<ffff20000811b4c4>]
> _local_bh_enable+0x4c/0x80 kernel/softirq.c:155
> softirqs last disabled at (2316913): [<     inline     >]
> do_softirq_own_stack ./include/linux/interrupt.h:488
> softirqs last disabled at (2316913): [<     inline     >]
> invoke_softirq kernel/softirq.c:371
> softirqs last disabled at (2316913): [<ffff20000811c994>]
> irq_exit+0x264/0x308 kernel/softirq.c:405
>
> other info that might help us debug this:
>  Possible unsafe locking scenario:
>
>        CPU0
>        ----
>   lock(ucounts_lock);
>   <Interrupt>
>     lock(ucounts_lock);
>
>  *** DEADLOCK ***
>
> 1 lock held by swapper/2/0:
>  #0:  (rcu_callback){......}, at: [<     inline     >] __rcu_reclaim
> kernel/rcu/rcu.h:108
>  #0:  (rcu_callback){......}, at: [<     inline     >] rcu_do_batch
> kernel/rcu/tree.c:2919
>  #0:  (rcu_callback){......}, at: [<     inline     >]
> invoke_rcu_callbacks kernel/rcu/tree.c:3182
>  #0:  (rcu_callback){......}, at: [<     inline     >]
> __rcu_process_callbacks kernel/rcu/tree.c:3149
>  #0:  (rcu_callback){......}, at: [<ffff200008210390>]
> rcu_process_callbacks+0x720/0xc28 kernel/rcu/tree.c:3166
>
> stack backtrace:
> CPU: 2 PID: 0 Comm: swapper/2 Not tainted 4.10.0-rc3-next-20170112-xc2-dirty #6
> Hardware name: Hardkernel ODROID-C2 (DT)
> Call trace:
> [<ffff20000808fa60>] dump_backtrace+0x0/0x440 arch/arm64/kernel/traps.c:500
> [<ffff20000808fec0>] show_stack+0x20/0x30 arch/arm64/kernel/traps.c:225
> [<ffff2000088a99e0>] dump_stack+0x110/0x168
> [<ffff2000082fa2b4>] print_usage_bug.part.27+0x49c/0x4bc
> kernel/locking/lockdep.c:2387
> [<     inline     >] print_usage_bug kernel/locking/lockdep.c:2357
> [<     inline     >] valid_state kernel/locking/lockdep.c:2400
> [<     inline     >] mark_lock_irq kernel/locking/lockdep.c:2617
> [<ffff2000081c89ec>] mark_lock+0x934/0xb60 kernel/locking/lockdep.c:3065
> [<     inline     >] mark_irqflags kernel/locking/lockdep.c:2923
> [<ffff2000081c9a60>] __lock_acquire+0x640/0x3260 kernel/locking/lockdep.c:3295
> [<ffff2000081cce24>] lock_acquire+0xa4/0x138 kernel/locking/lockdep.c:3753
> [<     inline     >] __raw_spin_lock ./include/linux/spinlock_api_smp.h:144
> [<ffff200009798128>] _raw_spin_lock+0x90/0xd0 kernel/locking/spinlock.c:151
> [<     inline     >] spin_lock ./include/linux/spinlock.h:302
> [<ffff2000081678c8>] put_ucounts+0x60/0x138 kernel/ucount.c:162
> [<ffff200008168364>] dec_ucount+0xf4/0x158 kernel/ucount.c:214
> [<     inline     >] dec_pid_namespaces kernel/pid_namespace.c:89
> [<ffff200008293dc8>] delayed_free_pidns+0x40/0xe0 kernel/pid_namespace.c:156
> [<     inline     >] __rcu_reclaim kernel/rcu/rcu.h:118
> [<     inline     >] rcu_do_batch kernel/rcu/tree.c:2919
> [<     inline     >] invoke_rcu_callbacks kernel/rcu/tree.c:3182
> [<     inline     >] __rcu_process_callbacks kernel/rcu/tree.c:3149
> [<ffff2000082103d8>] rcu_process_callbacks+0x768/0xc28 kernel/rcu/tree.c:3166
> [<ffff2000080821dc>] __do_softirq+0x324/0x6e0 kernel/softirq.c:284
> [<     inline     >] do_softirq_own_stack ./include/linux/interrupt.h:488
> [<     inline     >] invoke_softirq kernel/softirq.c:371
> [<ffff20000811c994>] irq_exit+0x264/0x308 kernel/softirq.c:405
> [<ffff2000081ecc28>] __handle_domain_irq+0xc0/0x150 kernel/irq/irqdesc.c:636
> [<ffff200008081c80>] gic_handle_irq+0x68/0xd8
> Exception stack(0xffff8000648e7dd0 to 0xffff8000648e7f00)
> 7dc0:                                   ffff8000648d4b3c 0000000000000007
> 7de0: 0000000000000000 1ffff0000c91a967 1ffff0000c91a967 1ffff0000c91a967
> 7e00: ffff20000a4b6b68 0000000000000001 0000000000000007 0000000000000001
> 7e20: 1fffe4000149ae90 ffff200009d35000 0000000000000000 0000000000000002
> 7e40: 0000000000000000 0000000000000000 0000000002624a1a 0000000000000000
> 7e60: 0000000000000000 ffff200009cbcd88 000060006d2ed000 0000000000000140
> 7e80: ffff200009cff000 ffff200009cb6000 ffff200009cc2020 ffff200009d2159d
> 7ea0: 0000000000000000 ffff8000648d4380 0000000000000000 ffff8000648e7f00
> 7ec0: ffff20000820a478 ffff8000648e7f00 ffff20000820a47c 0000000010000145
> 7ee0: 0000000000000140 dfff200000000000 ffffffffffffffff ffff20000820a478
> [<ffff2000080837f8>] el1_irq+0xb8/0x130 arch/arm64/kernel/entry.S:486
> [<     inline     >] arch_local_irq_restore
> ./arch/arm64/include/asm/irqflags.h:81
> [<ffff20000820a47c>] rcu_idle_exit+0x64/0xa8 kernel/rcu/tree.c:1030
> [<     inline     >] cpuidle_idle_call kernel/sched/idle.c:200
> [<ffff2000081bcbfc>] do_idle+0x1dc/0x2d0 kernel/sched/idle.c:243
> [<ffff2000081bd1cc>] cpu_startup_entry+0x24/0x28 kernel/sched/idle.c:345
> [<ffff200008099f8c>] secondary_start_kernel+0x2cc/0x358
> arch/arm64/kernel/smp.c:276
> [<000000000279f1a4>] 0x279f1a4

Reported-by: Dmitry Vyukov <dvyukov@google.com>
Tested-by: Dmitry Vyukov <dvyukov@google.com>
Fixes: add7c65ca4 ("pid: fix lockdep deadlock warning due to ucount_lock")
Fixes: f333c700c6 ("pidns: Add a limit on the number of pid namespaces")
Cc: stable@vger.kernel.org
Link: https://www.spinics.net/lists/kernel/msg2426637.html
Signed-off-by: Nikolay Borisov <n.borisov.lkml@gmail.com>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
2017-01-24 06:23:51 +13:00

238 lines
5.5 KiB
C

/*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License as
* published by the Free Software Foundation, version 2 of the
* License.
*/
#include <linux/stat.h>
#include <linux/sysctl.h>
#include <linux/slab.h>
#include <linux/hash.h>
#include <linux/user_namespace.h>
#define UCOUNTS_HASHTABLE_BITS 10
static struct hlist_head ucounts_hashtable[(1 << UCOUNTS_HASHTABLE_BITS)];
static DEFINE_SPINLOCK(ucounts_lock);
#define ucounts_hashfn(ns, uid) \
hash_long((unsigned long)__kuid_val(uid) + (unsigned long)(ns), \
UCOUNTS_HASHTABLE_BITS)
#define ucounts_hashentry(ns, uid) \
(ucounts_hashtable + ucounts_hashfn(ns, uid))
#ifdef CONFIG_SYSCTL
static struct ctl_table_set *
set_lookup(struct ctl_table_root *root)
{
return &current_user_ns()->set;
}
static int set_is_seen(struct ctl_table_set *set)
{
return &current_user_ns()->set == set;
}
static int set_permissions(struct ctl_table_header *head,
struct ctl_table *table)
{
struct user_namespace *user_ns =
container_of(head->set, struct user_namespace, set);
int mode;
/* Allow users with CAP_SYS_RESOURCE unrestrained access */
if (ns_capable(user_ns, CAP_SYS_RESOURCE))
mode = (table->mode & S_IRWXU) >> 6;
else
/* Allow all others at most read-only access */
mode = table->mode & S_IROTH;
return (mode << 6) | (mode << 3) | mode;
}
static struct ctl_table_root set_root = {
.lookup = set_lookup,
.permissions = set_permissions,
};
static int zero = 0;
static int int_max = INT_MAX;
#define UCOUNT_ENTRY(name) \
{ \
.procname = name, \
.maxlen = sizeof(int), \
.mode = 0644, \
.proc_handler = proc_dointvec_minmax, \
.extra1 = &zero, \
.extra2 = &int_max, \
}
static struct ctl_table user_table[] = {
UCOUNT_ENTRY("max_user_namespaces"),
UCOUNT_ENTRY("max_pid_namespaces"),
UCOUNT_ENTRY("max_uts_namespaces"),
UCOUNT_ENTRY("max_ipc_namespaces"),
UCOUNT_ENTRY("max_net_namespaces"),
UCOUNT_ENTRY("max_mnt_namespaces"),
UCOUNT_ENTRY("max_cgroup_namespaces"),
{ }
};
#endif /* CONFIG_SYSCTL */
bool setup_userns_sysctls(struct user_namespace *ns)
{
#ifdef CONFIG_SYSCTL
struct ctl_table *tbl;
setup_sysctl_set(&ns->set, &set_root, set_is_seen);
tbl = kmemdup(user_table, sizeof(user_table), GFP_KERNEL);
if (tbl) {
int i;
for (i = 0; i < UCOUNT_COUNTS; i++) {
tbl[i].data = &ns->ucount_max[i];
}
ns->sysctls = __register_sysctl_table(&ns->set, "user", tbl);
}
if (!ns->sysctls) {
kfree(tbl);
retire_sysctl_set(&ns->set);
return false;
}
#endif
return true;
}
void retire_userns_sysctls(struct user_namespace *ns)
{
#ifdef CONFIG_SYSCTL
struct ctl_table *tbl;
tbl = ns->sysctls->ctl_table_arg;
unregister_sysctl_table(ns->sysctls);
retire_sysctl_set(&ns->set);
kfree(tbl);
#endif
}
static struct ucounts *find_ucounts(struct user_namespace *ns, kuid_t uid, struct hlist_head *hashent)
{
struct ucounts *ucounts;
hlist_for_each_entry(ucounts, hashent, node) {
if (uid_eq(ucounts->uid, uid) && (ucounts->ns == ns))
return ucounts;
}
return NULL;
}
static struct ucounts *get_ucounts(struct user_namespace *ns, kuid_t uid)
{
struct hlist_head *hashent = ucounts_hashentry(ns, uid);
struct ucounts *ucounts, *new;
spin_lock_irq(&ucounts_lock);
ucounts = find_ucounts(ns, uid, hashent);
if (!ucounts) {
spin_unlock_irq(&ucounts_lock);
new = kzalloc(sizeof(*new), GFP_KERNEL);
if (!new)
return NULL;
new->ns = ns;
new->uid = uid;
atomic_set(&new->count, 0);
spin_lock_irq(&ucounts_lock);
ucounts = find_ucounts(ns, uid, hashent);
if (ucounts) {
kfree(new);
} else {
hlist_add_head(&new->node, hashent);
ucounts = new;
}
}
if (!atomic_add_unless(&ucounts->count, 1, INT_MAX))
ucounts = NULL;
spin_unlock_irq(&ucounts_lock);
return ucounts;
}
static void put_ucounts(struct ucounts *ucounts)
{
unsigned long flags;
if (atomic_dec_and_test(&ucounts->count)) {
spin_lock_irqsave(&ucounts_lock, flags);
hlist_del_init(&ucounts->node);
spin_unlock_irqrestore(&ucounts_lock, flags);
kfree(ucounts);
}
}
static inline bool atomic_inc_below(atomic_t *v, int u)
{
int c, old;
c = atomic_read(v);
for (;;) {
if (unlikely(c >= u))
return false;
old = atomic_cmpxchg(v, c, c+1);
if (likely(old == c))
return true;
c = old;
}
}
struct ucounts *inc_ucount(struct user_namespace *ns, kuid_t uid,
enum ucount_type type)
{
struct ucounts *ucounts, *iter, *bad;
struct user_namespace *tns;
ucounts = get_ucounts(ns, uid);
for (iter = ucounts; iter; iter = tns->ucounts) {
int max;
tns = iter->ns;
max = READ_ONCE(tns->ucount_max[type]);
if (!atomic_inc_below(&iter->ucount[type], max))
goto fail;
}
return ucounts;
fail:
bad = iter;
for (iter = ucounts; iter != bad; iter = iter->ns->ucounts)
atomic_dec(&iter->ucount[type]);
put_ucounts(ucounts);
return NULL;
}
void dec_ucount(struct ucounts *ucounts, enum ucount_type type)
{
struct ucounts *iter;
for (iter = ucounts; iter; iter = iter->ns->ucounts) {
int dec = atomic_dec_if_positive(&iter->ucount[type]);
WARN_ON_ONCE(dec < 0);
}
put_ucounts(ucounts);
}
static __init int user_namespace_sysctl_init(void)
{
#ifdef CONFIG_SYSCTL
static struct ctl_table_header *user_header;
static struct ctl_table empty[1];
/*
* It is necessary to register the user directory in the
* default set so that registrations in the child sets work
* properly.
*/
user_header = register_sysctl("user", empty);
BUG_ON(!user_header);
BUG_ON(!setup_userns_sysctls(&init_user_ns));
#endif
return 0;
}
subsys_initcall(user_namespace_sysctl_init);