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124 lines
3.7 KiB
Diff
124 lines
3.7 KiB
Diff
From 8ba8682107ee2ca3347354e018865d8e1967c5f4 Mon Sep 17 00:00:00 2001
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From: Omar Sandoval <osandov@fb.com>
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Date: Fri, 1 Jul 2016 00:39:35 -0700
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Subject: block: fix use-after-free in sys_ioprio_get()
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get_task_ioprio() accesses the task->io_context without holding the task
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lock and thus can race with exit_io_context(), leading to a
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use-after-free. The reproducer below hits this within a few seconds on
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my 4-core QEMU VM:
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#define _GNU_SOURCE
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#include <assert.h>
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#include <unistd.h>
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#include <sys/syscall.h>
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#include <sys/wait.h>
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int main(int argc, char **argv)
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{
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pid_t pid, child;
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long nproc, i;
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/* ioprio_set(IOPRIO_WHO_PROCESS, 0, IOPRIO_PRIO_VALUE(IOPRIO_CLASS_IDLE, 0)); */
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syscall(SYS_ioprio_set, 1, 0, 0x6000);
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nproc = sysconf(_SC_NPROCESSORS_ONLN);
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for (i = 0; i < nproc; i++) {
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pid = fork();
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assert(pid != -1);
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if (pid == 0) {
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for (;;) {
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pid = fork();
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assert(pid != -1);
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if (pid == 0) {
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_exit(0);
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} else {
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child = wait(NULL);
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assert(child == pid);
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}
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}
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}
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pid = fork();
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assert(pid != -1);
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if (pid == 0) {
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for (;;) {
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/* ioprio_get(IOPRIO_WHO_PGRP, 0); */
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syscall(SYS_ioprio_get, 2, 0);
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}
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}
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}
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for (;;) {
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/* ioprio_get(IOPRIO_WHO_PGRP, 0); */
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syscall(SYS_ioprio_get, 2, 0);
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}
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return 0;
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}
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This gets us KASAN dumps like this:
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[ 35.526914] ==================================================================
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[ 35.530009] BUG: KASAN: out-of-bounds in get_task_ioprio+0x7b/0x90 at addr ffff880066f34e6c
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[ 35.530009] Read of size 2 by task ioprio-gpf/363
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[ 35.530009] =============================================================================
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[ 35.530009] BUG blkdev_ioc (Not tainted): kasan: bad access detected
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[ 35.530009] -----------------------------------------------------------------------------
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[ 35.530009] Disabling lock debugging due to kernel taint
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[ 35.530009] INFO: Allocated in create_task_io_context+0x2b/0x370 age=0 cpu=0 pid=360
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[ 35.530009] ___slab_alloc+0x55d/0x5a0
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[ 35.530009] __slab_alloc.isra.20+0x2b/0x40
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[ 35.530009] kmem_cache_alloc_node+0x84/0x200
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[ 35.530009] create_task_io_context+0x2b/0x370
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[ 35.530009] get_task_io_context+0x92/0xb0
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[ 35.530009] copy_process.part.8+0x5029/0x5660
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[ 35.530009] _do_fork+0x155/0x7e0
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[ 35.530009] SyS_clone+0x19/0x20
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[ 35.530009] do_syscall_64+0x195/0x3a0
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[ 35.530009] return_from_SYSCALL_64+0x0/0x6a
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[ 35.530009] INFO: Freed in put_io_context+0xe7/0x120 age=0 cpu=0 pid=1060
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[ 35.530009] __slab_free+0x27b/0x3d0
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[ 35.530009] kmem_cache_free+0x1fb/0x220
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[ 35.530009] put_io_context+0xe7/0x120
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[ 35.530009] put_io_context_active+0x238/0x380
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[ 35.530009] exit_io_context+0x66/0x80
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[ 35.530009] do_exit+0x158e/0x2b90
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[ 35.530009] do_group_exit+0xe5/0x2b0
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[ 35.530009] SyS_exit_group+0x1d/0x20
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[ 35.530009] entry_SYSCALL_64_fastpath+0x1a/0xa4
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[ 35.530009] INFO: Slab 0xffffea00019bcd00 objects=20 used=4 fp=0xffff880066f34ff0 flags=0x1fffe0000004080
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[ 35.530009] INFO: Object 0xffff880066f34e58 @offset=3672 fp=0x0000000000000001
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[ 35.530009] ==================================================================
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Fix it by grabbing the task lock while we poke at the io_context.
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Cc: stable@vger.kernel.org
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Reported-by: Dmitry Vyukov <dvyukov@google.com>
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Signed-off-by: Omar Sandoval <osandov@fb.com>
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Signed-off-by: Jens Axboe <axboe@fb.com>
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---
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block/ioprio.c | 2 ++
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1 file changed, 2 insertions(+)
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diff --git a/block/ioprio.c b/block/ioprio.c
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index cc7800e..01b8116 100644
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--- a/block/ioprio.c
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+++ b/block/ioprio.c
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@@ -150,8 +150,10 @@ static int get_task_ioprio(struct task_struct *p)
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if (ret)
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goto out;
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ret = IOPRIO_PRIO_VALUE(IOPRIO_CLASS_NONE, IOPRIO_NORM);
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+ task_lock(p);
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if (p->io_context)
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ret = p->io_context->ioprio;
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+ task_unlock(p);
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out:
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return ret;
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}
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--
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cgit v1.1
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