KMSAN: uninit-value in sr_check_events

[Dipanjan Das]

Hi,

We would like to report the following bug which has been found by our
modified version of syzkaller.

======================================================
description: KMSAN: uninit-value in sr_check_events
affected file: drivers/scsi/sr.c
kernel version: 6.2.0-rc5
kernel commit: 41c66f47061608dc1fd493eebce198f0e74cc2d7
git tree: kmsan
kernel config: https://syzkaller.appspot.com/text?tag=KernelConfig&x=a9a22da1efde3af6
crash reproducer: attached
======================================================
Crash log:
======================================================
BUG: KMSAN: uninit-value in sr_check_events+0x12d2/0x13c0 drivers/scsi/sr.c:269
 sr_check_events+0x12d2/0x13c0 drivers/scsi/sr.c:269
 cdrom_update_events drivers/cdrom/cdrom.c:1485 [inline]
 cdrom_check_events+0x61/0x170 drivers/cdrom/cdrom.c:1495
 sr_block_check_events+0xf5/0x130 drivers/scsi/sr.c:559
 disk_check_events+0xf1/0x950 block/disk-events.c:193
 disk_clear_events block/disk-events.c:248 [inline]
 bdev_check_media_change+0x26a/0x7f0 block/disk-events.c:279
 sr_block_open+0x159/0x340 drivers/scsi/sr.c:494
 blkdev_get_whole+0xb4/0x700 block/bdev.c:672
 blkdev_get_by_dev+0x4c9/0x1280 block/bdev.c:822
 blkdev_open+0x216/0x440 block/fops.c:478
 do_dentry_open+0xf85/0x1970 fs/open.c:882
 vfs_open+0x75/0xa0 fs/open.c:1013
 do_open fs/namei.c:3557 [inline]
 path_openat+0x4c4b/0x5a00 fs/namei.c:3714
 do_filp_open+0x252/0x660 fs/namei.c:3741
 do_sys_openat2+0x200/0x920 fs/open.c:1310
 do_sys_open fs/open.c:1326 [inline]
 __do_sys_openat fs/open.c:1342 [inline]
 __se_sys_openat fs/open.c:1337 [inline]
 __x64_sys_openat+0x285/0x310 fs/open.c:1337
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

Uninit was stored to memory at:
 sr_check_events+0xb04/0x13c0 drivers/scsi/sr.c:216
 cdrom_update_events drivers/cdrom/cdrom.c:1485 [inline]
 cdrom_check_events+0x61/0x170 drivers/cdrom/cdrom.c:1495
 sr_block_check_events+0xf5/0x130 drivers/scsi/sr.c:559
 disk_check_events+0xf1/0x950 block/disk-events.c:193
 disk_clear_events block/disk-events.c:248 [inline]
 bdev_check_media_change+0x26a/0x7f0 block/disk-events.c:279
 sr_block_open+0x159/0x340 drivers/scsi/sr.c:494
 blkdev_get_whole+0xb4/0x700 block/bdev.c:672
 blkdev_get_by_dev+0x4c9/0x1280 block/bdev.c:822
 blkdev_open+0x216/0x440 block/fops.c:478
 do_dentry_open+0xf85/0x1970 fs/open.c:882
 vfs_open+0x75/0xa0 fs/open.c:1013
 do_open fs/namei.c:3557 [inline]
 path_openat+0x4c4b/0x5a00 fs/namei.c:3714
 do_filp_open+0x252/0x660 fs/namei.c:3741
 do_sys_openat2+0x200/0x920 fs/open.c:1310
 do_sys_open fs/open.c:1326 [inline]
 __do_sys_openat fs/open.c:1342 [inline]
 __se_sys_openat fs/open.c:1337 [inline]
 __x64_sys_openat+0x285/0x310 fs/open.c:1337
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

Local variable sshdr.i created at:
 sr_get_events drivers/scsi/sr.c:172 [inline]
 sr_check_events+0x11f/0x13c0 drivers/scsi/sr.c:215
 cdrom_update_events drivers/cdrom/cdrom.c:1485 [inline]
 cdrom_check_events+0x61/0x170 drivers/cdrom/cdrom.c:1495

CPU: 0 PID: 22994 Comm: syz-executor.1 Not tainted
6.2.0-rc5-00010-g41c66f470616 #8
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
1.13.0-1ubuntu1.1 04/01/2014

-- 
Thanks and Regards,

Dipanjan

Attachment: repro.syz
Description: Binary data

// autogenerated by syzkaller (https://github.com/google/syzkaller)

#define _GNU_SOURCE 

#include <dirent.h>
#include <endian.h>
#include <errno.h>
#include <fcntl.h>
#include <signal.h>
#include <stdarg.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/prctl.h>
#include <sys/stat.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <time.h>
#include <unistd.h>

static void sleep_ms(uint64_t ms)
{
	usleep(ms * 1000);
}

static uint64_t current_time_ms(void)
{
	struct timespec ts;
	if (clock_gettime(CLOCK_MONOTONIC, &ts))
	exit(1);
	return (uint64_t)ts.tv_sec * 1000 + (uint64_t)ts.tv_nsec / 1000000;
}

static bool write_file(const char* file, const char* what, ...)
{
	char buf[1024];
	va_list args;
	va_start(args, what);
	vsnprintf(buf, sizeof(buf), what, args);
	va_end(args);
	buf[sizeof(buf) - 1] = 0;
	int len = strlen(buf);
	int fd = open(file, O_WRONLY | O_CLOEXEC);
	if (fd == -1)
		return false;
	if (write(fd, buf, len) != len) {
		int err = errno;
		close(fd);
		errno = err;
		return false;
	}
	close(fd);
	return true;
}

static int inject_fault(int nth)
{
	int fd;
	fd = open("/proc/thread-self/fail-nth", O_RDWR);
	if (fd == -1)
	exit(1);
	char buf[16];
	sprintf(buf, "%d", nth);
	if (write(fd, buf, strlen(buf)) != (ssize_t)strlen(buf))
	exit(1);
	return fd;
}

static void kill_and_wait(int pid, int* status)
{
	kill(-pid, SIGKILL);
	kill(pid, SIGKILL);
	for (int i = 0; i < 100; i++) {
		if (waitpid(-1, status, WNOHANG | __WALL) == pid)
			return;
		usleep(1000);
	}
	DIR* dir = opendir("/sys/fs/fuse/connections");
	if (dir) {
		for (;;) {
			struct dirent* ent = readdir(dir);
			if (!ent)
				break;
			if (strcmp(ent->d_name, ".") == 0 || strcmp(ent->d_name, "..") == 0)
				continue;
			char abort[300];
			snprintf(abort, sizeof(abort), "/sys/fs/fuse/connections/%s/abort", ent->d_name);
			int fd = open(abort, O_WRONLY);
			if (fd == -1) {
				continue;
			}
			if (write(fd, abort, 1) < 0) {
			}
			close(fd);
		}
		closedir(dir);
	} else {
	}
	while (waitpid(-1, status, __WALL) != pid) {
	}
}

static void setup_test()
{
	prctl(PR_SET_PDEATHSIG, SIGKILL, 0, 0, 0);
	setpgrp();
	write_file("/proc/self/oom_score_adj", "1000");
}

static void setup_fault()
{
	static struct {
		const char* file;
		const char* val;
		bool fatal;
	} files[] = {
	    {"/sys/kernel/debug/failslab/ignore-gfp-wait", "N", true},
	    {"/sys/kernel/debug/fail_futex/ignore-private", "N", false},
	    {"/sys/kernel/debug/fail_page_alloc/ignore-gfp-highmem", "N", false},
	    {"/sys/kernel/debug/fail_page_alloc/ignore-gfp-wait", "N", false},
	    {"/sys/kernel/debug/fail_page_alloc/min-order", "0", false},
	};
	unsigned i;
	for (i = 0; i < sizeof(files) / sizeof(files[0]); i++) {
		if (!write_file(files[i].file, files[i].val)) {
			if (files[i].fatal)
	exit(1);
		}
	}
}

static void execute_one(void);

#define WAIT_FLAGS __WALL

static void loop(void)
{
	int iter = 0;
	for (;; iter++) {
		int pid = fork();
		if (pid < 0)
	exit(1);
		if (pid == 0) {
			setup_test();
			execute_one();
			exit(0);
		}
		int status = 0;
		uint64_t start = current_time_ms();
		for (;;) {
			if (waitpid(-1, &status, WNOHANG | WAIT_FLAGS) == pid)
				break;
			sleep_ms(1);
			if (current_time_ms() - start < 5000)
				continue;
			kill_and_wait(pid, &status);
			break;
		}
	}
}

void execute_one(void)
{
memcpy((void*)0x20000040, "/dev/sr0\000", 9);
	inject_fault(7);
	syscall(__NR_openat, 0xffffffffffffff9cul, 0x20000040ul, 0x48800ul, 0ul);

}
int main(void)
{
		syscall(__NR_mmap, 0x1ffff000ul, 0x1000ul, 0ul, 0x32ul, -1, 0ul);
	syscall(__NR_mmap, 0x20000000ul, 0x1000000ul, 7ul, 0x32ul, -1, 0ul);
	syscall(__NR_mmap, 0x21000000ul, 0x1000ul, 0ul, 0x32ul, -1, 0ul);
	setup_fault();
			loop();
	return 0;
}