On 06/01/2017 02:39, Wanpeng Li wrote:
> From: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
>
> Reported syzkaller:
>
> BUG: unable to handle kernel NULL pointer dereference at 0000000000000008
> IP: irq_bypass_unregister_consumer+0x9d/0xb70 [irqbypass]
> PGD 0
>
> Oops: 0002 [#1] SMP
> CPU: 1 PID: 125 Comm: kworker/1:1 Not tainted 4.9.0+ #1
> Workqueue: kvm-irqfd-cleanup irqfd_shutdown [kvm]
> task: ffff9bbe0dfbb900 task.stack: ffffb61802014000
> RIP: 0010:irq_bypass_unregister_consumer+0x9d/0xb70 [irqbypass]
> Call Trace:
> irqfd_shutdown+0x66/0xa0 [kvm]
> process_one_work+0x16b/0x480
> worker_thread+0x4b/0x500
> kthread+0x101/0x140
> ? process_one_work+0x480/0x480
> ? kthread_create_on_node+0x60/0x60
> ret_from_fork+0x25/0x30
> RIP: irq_bypass_unregister_consumer+0x9d/0xb70 [irqbypass] RSP: ffffb61802017e20
> CR2: 0000000000000008
>
> The syzkaller folks reported a NULL pointer dereference that due to
> unregister an consumer which fails registration before. The syzkaller
> creates two VMs w/ an equal eventfd occasionally. So the second VM
> fails to register an irqbypass consumer. It will make irqfd as inactive
> and queue an workqueue work to shutdown irqfd and unregister the irqbypass
> consumer when eventfd is closed. However, the second consumer has been
> initialized though it fails registration. So the token(same as the first
> VM's) is taken to unregister the consumer through the workqueue, the
> consumer of the first VM is found and unregistered, then NULL deref incurred
> in the path of deleting consumer from the consumers list.
>
> #include <fcntl.h>
> #include <pthread.h>
> #include <setjmp.h>
> #include <signal.h>
> #include <stddef.h>
> #include <stdint.h>
> #include <stdio.h>
> #include <stdlib.h>
> #include <string.h>
> #include <sys/ioctl.h>
> #include <sys/stat.h>
> #include <sys/syscall.h>
> #include <sys/types.h>
> #include <unistd.h>
>
> __thread int skip_segv;
> __thread jmp_buf segv_env;
>
> static void segv_handler(int sig, siginfo_t* info, void* uctx)
> {
> if (__atomic_load_n(&skip_segv, __ATOMIC_RELAXED))
> _longjmp(segv_env, 1);
> exit(sig);
> }
>
> static void install_segv_handler()
> {
> struct sigaction sa;
> memset(&sa, 0, sizeof(sa));
> sa.sa_sigaction = segv_handler;
> sa.sa_flags = SA_NODEFER | SA_SIGINFO;
> sigaction(SIGSEGV, &sa, NULL);
> sigaction(SIGBUS, &sa, NULL);
> }
>
> #define NONFAILING(...) \
> { \
> __atomic_fetch_add(&skip_segv, 1, __ATOMIC_SEQ_CST); \
> if (_setjmp(segv_env) == 0) { \
> __VA_ARGS__; \
> } \
> __atomic_fetch_sub(&skip_segv, 1, __ATOMIC_SEQ_CST); \
> }
>
> static uintptr_t execute_syscall(int nr, uintptr_t a0, uintptr_t a1,
> uintptr_t a2, uintptr_t a3,
> uintptr_t a4, uintptr_t a5,
> uintptr_t a6, uintptr_t a7,
> uintptr_t a8)
> {
> return syscall(nr, a0, a1, a2, a3, a4, a5);
> }
>
> long r[28];
> void* thr(void* arg)
> {
> switch ((long)arg) {
> case 0:
> r[0] =
> execute_syscall(__NR_mmap, 0x20000000ul, 0xd000ul, 0x3ul,
> 0x32ul, 0xfffffffffffffffful, 0x0ul, 0, 0, 0);
> break;
> case 1:
> r[2] = syscall(__NR_open, "/dev/kvm", 0x40042ul, 0, 0, 0, 0, 0, 0);
> break;
> case 2:
> r[3] = execute_syscall(__NR_ioctl, r[2], 0xae01ul, 0x0ul, 0, 0, 0,
> 0, 0, 0);
> break;
> case 3:
> r[4] = execute_syscall(__NR_ioctl, r[3], 0xae41ul, 0x3fful, 0, 0, 0,
> 0, 0, 0);
> break;
> case 4:
> r[5] = execute_syscall(__NR_ioctl, r[4], 0xae9aul, 0, 0, 0, 0, 0, 0,
> 0);
> break;
> case 5:
> r[6] = execute_syscall(__NR_eventfd2, 0x8ul, 0x801ul, 0, 0, 0, 0, 0,
> 0, 0);
> break;
> case 6:
> NONFAILING(*(uint32_t*)0x2000c000 = r[6]);
> NONFAILING(*(uint32_t*)0x2000c004 = (uint32_t)0x98cd);
> NONFAILING(*(uint32_t*)0x2000c008 = (uint32_t)0x0);
> NONFAILING(*(uint32_t*)0x2000c00c = (uint32_t)0xffffffffffffffff);
> NONFAILING(*(uint8_t*)0x2000c010 = (uint8_t)0x0);
> NONFAILING(*(uint8_t*)0x2000c011 = (uint8_t)0x0);
> NONFAILING(*(uint8_t*)0x2000c012 = (uint8_t)0x0);
> NONFAILING(*(uint8_t*)0x2000c013 = (uint8_t)0x0);
> NONFAILING(*(uint8_t*)0x2000c014 = (uint8_t)0x0);
> NONFAILING(*(uint8_t*)0x2000c015 = (uint8_t)0x0);
> NONFAILING(*(uint8_t*)0x2000c016 = (uint8_t)0x0);
> NONFAILING(*(uint8_t*)0x2000c017 = (uint8_t)0x0);
> NONFAILING(*(uint8_t*)0x2000c018 = (uint8_t)0x0);
> NONFAILING(*(uint8_t*)0x2000c019 = (uint8_t)0x0);
> NONFAILING(*(uint8_t*)0x2000c01a = (uint8_t)0x0);
> NONFAILING(*(uint8_t*)0x2000c01b = (uint8_t)0x0);
> NONFAILING(*(uint8_t*)0x2000c01c = (uint8_t)0x0);
> NONFAILING(*(uint8_t*)0x2000c01d = (uint8_t)0x0);
> NONFAILING(*(uint8_t*)0x2000c01e = (uint8_t)0x0);
> NONFAILING(*(uint8_t*)0x2000c01f = (uint8_t)0x0);
> r[27] = execute_syscall(__NR_ioctl, r[3], 0x4020ae76ul,
> 0x2000c000ul, 0, 0, 0, 0, 0, 0);
> break;
> }
> return 0;
> }
>
> int main()
> {
> long i;
> pthread_t th[14];
>
> install_segv_handler();
> memset(r, -1, sizeof(r));
> srand(getpid());
> for (i = 0; i < 7; i++) {
> pthread_create(&th[i], 0, thr, (void*)i);
> usleep(10000);
> }
> for (i = 0; i < 7; i++) {
> pthread_create(&th[7 + i], 0, thr, (void*)i);
> if (rand() % 2)
> usleep(rand() % 10000);
> }
> usleep(100000);
> return 0;
> }
>
> This patch fixes it by making irq_bypass_register/unregister_consumer()
> looks for the consumer entry based on consumer pointer itself instead of
> token matching.
>
> Reported-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
> Suggested-by: Alex Williamson <alex.williamson@xxxxxxxxxx>
> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> Cc: Radim Krčmář <rkrcmar@xxxxxxxxxx>
> Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
> Cc: Alex Williamson <alex.williamson@xxxxxxxxxx>
> Signed-off-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
> ---
> v1 -> v2:
> * make irq_bypass_register/unregister_consumer() looks for the consumer
> entry based on consumer pointer itself instead of token matching
>
> virt/lib/irqbypass.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/virt/lib/irqbypass.c b/virt/lib/irqbypass.c
> index 52abac4..6d2fcd6 100644
> --- a/virt/lib/irqbypass.c
> +++ b/virt/lib/irqbypass.c
> @@ -195,7 +195,7 @@ int irq_bypass_register_consumer(struct irq_bypass_consumer *consumer)
> mutex_lock(&lock);
>
> list_for_each_entry(tmp, &consumers, node) {
> - if (tmp->token == consumer->token) {
> + if (tmp->token == consumer->token || tmp == consumer) {
> mutex_unlock(&lock);
> module_put(THIS_MODULE);
> return -EBUSY;
> @@ -245,7 +245,7 @@ void irq_bypass_unregister_consumer(struct irq_bypass_consumer *consumer)
> mutex_lock(&lock);
>
> list_for_each_entry(tmp, &consumers, node) {
> - if (tmp->token != consumer->token)
> + if (tmp != consumer)
> continue;
>
> list_for_each_entry(producer, &producers, node) {
>
Acked-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
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