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Omar Sandoval 60b67e2584 block: fix use-after-free in sys_ioprio_get() 
commit 8ba8682107 upstream.

get_task_ioprio() accesses the task->io_context without holding the task
lock and thus can race with exit_io_context(), leading to a
use-after-free. The reproducer below hits this within a few seconds on
my 4-core QEMU VM:

#define _GNU_SOURCE
#include <assert.h>
#include <unistd.h>
#include <sys/syscall.h>
#include <sys/wait.h>

int main(int argc, char **argv)
{
	pid_t pid, child;
	long nproc, i;

	/* ioprio_set(IOPRIO_WHO_PROCESS, 0, IOPRIO_PRIO_VALUE(IOPRIO_CLASS_IDLE, 0)); */
	syscall(SYS_ioprio_set, 1, 0, 0x6000);

	nproc = sysconf(_SC_NPROCESSORS_ONLN);

	for (i = 0; i < nproc; i++) {
		pid = fork();
		assert(pid != -1);
		if (pid == 0) {
			for (;;) {
				pid = fork();
				assert(pid != -1);
				if (pid == 0) {
					_exit(0);
				} else {
					child = wait(NULL);
					assert(child == pid);
				}
			}
		}

		pid = fork();
		assert(pid != -1);
		if (pid == 0) {
			for (;;) {
				/* ioprio_get(IOPRIO_WHO_PGRP, 0); */
				syscall(SYS_ioprio_get, 2, 0);
			}
		}
	}

	for (;;) {
		/* ioprio_get(IOPRIO_WHO_PGRP, 0); */
		syscall(SYS_ioprio_get, 2, 0);
	}

	return 0;
}

This gets us KASAN dumps like this:

[   35.526914] ==================================================================
[   35.530009] BUG: KASAN: out-of-bounds in get_task_ioprio+0x7b/0x90 at addr ffff880066f34e6c
[   35.530009] Read of size 2 by task ioprio-gpf/363
[   35.530009] =============================================================================
[   35.530009] BUG blkdev_ioc (Not tainted): kasan: bad access detected
[   35.530009] -----------------------------------------------------------------------------

[   35.530009] Disabling lock debugging due to kernel taint
[   35.530009] INFO: Allocated in create_task_io_context+0x2b/0x370 age=0 cpu=0 pid=360
[   35.530009] 	___slab_alloc+0x55d/0x5a0
[   35.530009] 	__slab_alloc.isra.20+0x2b/0x40
[   35.530009] 	kmem_cache_alloc_node+0x84/0x200
[   35.530009] 	create_task_io_context+0x2b/0x370
[   35.530009] 	get_task_io_context+0x92/0xb0
[   35.530009] 	copy_process.part.8+0x5029/0x5660
[   35.530009] 	_do_fork+0x155/0x7e0
[   35.530009] 	SyS_clone+0x19/0x20
[   35.530009] 	do_syscall_64+0x195/0x3a0
[   35.530009] 	return_from_SYSCALL_64+0x0/0x6a
[   35.530009] INFO: Freed in put_io_context+0xe7/0x120 age=0 cpu=0 pid=1060
[   35.530009] 	__slab_free+0x27b/0x3d0
[   35.530009] 	kmem_cache_free+0x1fb/0x220
[   35.530009] 	put_io_context+0xe7/0x120
[   35.530009] 	put_io_context_active+0x238/0x380
[   35.530009] 	exit_io_context+0x66/0x80
[   35.530009] 	do_exit+0x158e/0x2b90
[   35.530009] 	do_group_exit+0xe5/0x2b0
[   35.530009] 	SyS_exit_group+0x1d/0x20
[   35.530009] 	entry_SYSCALL_64_fastpath+0x1a/0xa4
[   35.530009] INFO: Slab 0xffffea00019bcd00 objects=20 used=4 fp=0xffff880066f34ff0 flags=0x1fffe0000004080
[   35.530009] INFO: Object 0xffff880066f34e58 @offset=3672 fp=0x0000000000000001
[   35.530009] ==================================================================

Fix it by grabbing the task lock while we poke at the io_context.

Reported-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
History 2016-08-22 22:38:26 +01:00
..
partitions mac: validate mac_partition is within sector 2015-12-18 16:06:30 +00:00
bio-integrity.c bio integrity: do not assume bio_integrity_pool exists if bioset exists 2015-08-10 09:54:14 +01:00
bio.c bio: return EINTR if copying to user space got interrupted 2016-03-04 10:26:40 +00:00
blk-cgroup.c blkcg: fix gendisk reference leak in blkg_conf_prep() 2015-08-11 09:57:43 +01:00
blk-cgroup.h Revert "block: add __init to blkcg_policy_register" 2014-06-22 16:34:11 -06:00
blk-core.c SCSI: Fix NULL pointer dereference in runtime PM 2016-01-11 10:50:18 +00:00
blk-exec.c block: blk-exec.c: Cleaning up local variable address returnd 2014-06-08 19:51:31 -06:00
blk-flush.c block: remove elv_abort_queue and blk_abort_flushes 2014-06-11 15:31:21 -06:00
blk-integrity.c bio-integrity: Convert to bvec_iter 2013-11-23 22:33:50 -08:00
blk-ioc.c block: Substitute rcu_access_pointer() for rcu_dereference_raw() 2014-02-18 12:21:26 -08:00
blk-iopoll.c Merge branch 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip into next 2014-06-03 12:57:53 -07:00
blk-lib.c block/blk-lib.c: make __blkdev_issue_zeroout static 2014-05-26 17:39:09 -06:00
blk-map.c block: remove struct request buffer member 2014-04-15 14:03:02 -06:00
blk-merge.c Fix bug in blk_rq_merge_ok 2015-04-10 10:03:59 +01:00
blk-mq-cpu.c blk-mq: add file comments and update copyright notices 2014-05-28 10:15:41 -06:00
blk-mq-cpumap.c blk-mq: use 'nr_cpu_ids' as highest CPU ID count for hwq <-> cpu map 2015-01-12 15:43:57 +00:00
blk-mq-sysfs.c blk-mq: fix buffer overflow when reading sysfs file of 'pending' 2015-09-28 10:21:41 +01:00
blk-mq-tag.c blk-mq: fix double-free in error path 2015-03-02 13:17:12 +00:00
blk-mq-tag.h blk-mq: bitmap tag: fix races on shared ::wake_index fields 2014-06-17 22:12:35 -07:00
blk-mq.c blk-mq: fix undefined behaviour in order_to_size() 2016-08-22 22:37:59 +01:00
blk-mq.h blk-mq: fix schedule from atomic context 2014-06-03 21:04:39 -06:00
blk-settings.c block: fix alignment_offset math that assumes io_min is a power-of-2 2014-11-17 14:11:44 +00:00
blk-softirq.c block: fix regression with block enabled tagging 2014-04-09 21:54:06 -06:00
blk-sysfs.c blk-mq: Fix a use-after-free 2015-01-15 10:43:41 +00:00
blk-tag.c block: don't assume last put of shared tags is for the host 2014-07-08 12:25:28 +02:00
blk-throttle.c blk-throttle: check stats_cpu before reading it from sysfs 2015-03-02 15:04:36 +00:00
blk-timeout.c block: ensure that the timer is always added 2014-05-30 15:41:39 -06:00
blk.h block: remove elv_abort_queue and blk_abort_flushes 2014-06-11 15:31:21 -06:00
bounce.c mm: convert some level-less printks to pr_* 2014-06-06 16:08:18 -07:00
bsg-lib.c bsg: Remove unused function bsg_goose_queue() 2012-12-06 14:33:02 +01:00
bsg.c block: add blk_rq_set_block_pc() 2014-06-06 07:57:37 -06:00
cfq-iosched.c cfq-iosched: handle failure of cfq group allocation 2015-03-02 13:17:10 +00:00
cmdline-parser.c block: remove unrelated header files and export symbol 2014-01-21 20:18:26 -08:00
compat_ioctl.c block: provide compat ioctl for BLKZEROOUT 2014-07-14 12:27:20 +02:00
deadline-iosched.c block: Stop abusing csd.list for fifo_time 2014-02-24 14:46:32 -08:00
elevator.c Revert "block: add __init to elv_register" 2014-06-22 16:34:11 -06:00
genhd.c block: fix ext_dev_lock lockdep report 2015-06-30 17:15:25 +01:00
ioctl.c block: replace IS_ERR and PTR_ERR with PTR_ERR_OR_ZERO 2013-11-08 09:05:31 -07:00
ioprio.c block: fix use-after-free in sys_ioprio_get() 2016-08-22 22:38:26 +01:00
Kconfig block: change config option name for cmdline partition parsing 2013-09-30 14:31:02 -07:00
Kconfig.iosched blkcg: make CONFIG_BLK_CGROUP bool 2012-03-06 21:27:21 +01:00
Makefile block: move mm/bounce.c to block/ 2014-05-19 20:01:52 -06:00
noop-iosched.c elevator: Fix a race in elevator switching 2013-07-03 13:25:24 +02:00
partition-generic.c block: Fix dev_t minor allocation lifetime 2014-10-05 13:41:05 -07:00
scsi_ioctl.c scsi: Fix error handling in SCSI_IOCTL_SEND_COMMAND 2014-11-13 11:48:39 +00:00