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Subjectdrm: GPF in drm_legacy_lock_free
Hello,

The following program trigger GPF in drm_legacy_lock_free:

general protection fault: 0000 [#1] SMP DEBUG_PAGEALLOC KASAN
Modules linked in:
CPU: 2 PID: 3379 Comm: syz-executor Not tainted 4.8.0-rc3+ #35
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
task: ffff8800637840c0 task.stack: ffff880063fa8000
RIP: 0010:[<ffffffff8341a781>]
[<ffffffff8341a781>] drm_legacy_lock_free+0x2a1/0x3c0
drivers/gpu/drm/drm_lock.c:133
RSP: 0018:ffff880063fafa68 EFLAGS: 00010287
RAX: ffffffff8341a781 RBX: ffff880063fafc20 RCX: ffffc900040e4000
RDX: 0000000000000065 RSI: ffff880063784900 RDI: ffffffff884b8298
RBP: ffff880063fafc48 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: ffff88006821e580
R13: 0000000000000003 R14: 0000000000000000 R15: dffffc0000000000
FS: 00007f21ada94700(0000) GS:ffff88006d400000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000002000aff8 CR3: 000000003bcc4000 CR4: 00000000000006e0
Stack:
00000001004af988 1ffff1000c7f5f50 ffff88006821e5e0 0000000041b58ab3
ffffffff88116d28 ffffffff8341a4e0 ffffffff89e748d0 ffffffff8a3b4e60
ffff8800637848f0 ffff880063784918 ffff880063784920 ffff8800637848f8
Call Trace:
[<ffffffff8341b77a>] drm_legacy_unlock+0xda/0x170
drivers/gpu/drm/drm_lock.c:264
[<ffffffff834109fc>] drm_ioctl+0x7bc/0xc60 drivers/gpu/drm/drm_ioctl.c:724
[< inline >] vfs_ioctl fs/ioctl.c:43
[<ffffffff8186f1fc>] do_vfs_ioctl+0x18c/0x1080 fs/ioctl.c:675
[< inline >] SYSC_ioctl fs/ioctl.c:690
[<ffffffff8187017f>] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:681
[<ffffffff86c25400>] entry_SYSCALL_64_fastpath+0x23/0xc1
arch/x86/entry/entry_64.S:207
Code: ff ff 4d 89 f7 4d 89 f5 49 c1 ef 03 41 83 e5 07 41 83 c5 03 e8
61 a0 80 03 48 b8 00 00 00 00 00 fc ff df 49 01 c7 e8 5f 52 19 fe <41>
0f b6 07 41 38 c5 7c 08 84 c0 0f 85 f4 00 00 00 41 8b 3e 89
RIP [<ffffffff8341a781>] drm_legacy_lock_free+0x2a1/0x3c0
drivers/gpu/drm/drm_lock.c:133
RSP <ffff880063fafa68>
---[ end trace 0b3780f72376546b ]---
Kernel panic - not syncing: Fatal exception

On commit 61c04572de404e52a655a36752e696bbcb483cf5 (Aug 25)

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

#ifndef __NR_mmap
#define __NR_mmap 9
#endif
#ifndef __NR_syz_open_dev
#define __NR_syz_open_dev 1000001
#endif
#ifndef __NR_ioctl
#define __NR_ioctl 16
#endif
#ifndef __NR_syz_fuse_mount
#define __NR_syz_fuse_mount 1000003
#endif
#ifndef __NR_syz_fuseblk_mount
#define __NR_syz_fuseblk_mount 1000004
#endif
#ifndef __NR_syz_open_pts
#define __NR_syz_open_pts 1000002
#endif

#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 syz_open_dev(uintptr_t a0, uintptr_t a1, uintptr_t a2)
{
if (a0 == 0xc || a0 == 0xb) {
char buf[128];
sprintf(buf, "/dev/%s/%d:%d", a0 == 0xc ? "char" : "block",
(uint8_t)a1, (uint8_t)a2);
return open(buf, O_RDWR, 0);
} else {
char buf[1024];
char* hash;
strncpy(buf, (char*)a0, sizeof(buf));
buf[sizeof(buf) - 1] = 0;
while ((hash = strchr(buf, '#'))) {
*hash = '0' + (char)(a1 % 10);
a1 /= 10;
}
return open(buf, a2, 0);
}
}

static uintptr_t syz_open_pts(uintptr_t a0, uintptr_t a1)
{
int ptyno = 0;
if (ioctl(a0, TIOCGPTN, &ptyno))
return -1;
char buf[128];
sprintf(buf, "/dev/pts/%d", ptyno);
return open(buf, a1, 0);
}

static uintptr_t syz_fuse_mount(uintptr_t a0, uintptr_t a1,
uintptr_t a2, uintptr_t a3,
uintptr_t a4, uintptr_t a5)
{
uint64_t target = a0;
uint64_t mode = a1;
uint64_t uid = a2;
uint64_t gid = a3;
uint64_t maxread = a4;
uint64_t flags = a5;

int fd = open("/dev/fuse", O_RDWR);
if (fd == -1)
return fd;
char buf[1024];
sprintf(buf, "fd=%d,user_id=%ld,group_id=%ld,rootmode=0%o", fd,
(long)uid, (long)gid, (unsigned)mode & ~3u);
if (maxread != 0)
sprintf(buf + strlen(buf), ",max_read=%ld", (long)maxread);
if (mode & 1)
strcat(buf, ",default_permissions");
if (mode & 2)
strcat(buf, ",allow_other");
syscall(SYS_mount, "", target, "fuse", flags, buf);
return fd;
}

static uintptr_t syz_fuseblk_mount(uintptr_t a0, uintptr_t a1,
uintptr_t a2, uintptr_t a3,
uintptr_t a4, uintptr_t a5,
uintptr_t a6, uintptr_t a7)
{
uint64_t target = a0;
uint64_t blkdev = a1;
uint64_t mode = a2;
uint64_t uid = a3;
uint64_t gid = a4;
uint64_t maxread = a5;
uint64_t blksize = a6;
uint64_t flags = a7;

int fd = open("/dev/fuse", O_RDWR);
if (fd == -1)
return fd;
if (syscall(SYS_mknodat, AT_FDCWD, blkdev, S_IFBLK, makedev(7, 199)))
return fd;
char buf[256];
sprintf(buf, "fd=%d,user_id=%ld,group_id=%ld,rootmode=0%o", fd,
(long)uid, (long)gid, (unsigned)mode & ~3u);
if (maxread != 0)
sprintf(buf + strlen(buf), ",max_read=%ld", (long)maxread);
if (blksize != 0)
sprintf(buf + strlen(buf), ",blksize=%ld", (long)blksize);
if (mode & 1)
strcat(buf, ",default_permissions");
if (mode & 2)
strcat(buf, ",allow_other");
syscall(SYS_mount, blkdev, target, "fuseblk", flags, buf);
return fd;
}

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)
{
switch (nr) {
default:
return syscall(nr, a0, a1, a2, a3, a4, a5);
case __NR_syz_open_dev:
return syz_open_dev(a0, a1, a2);
case __NR_syz_open_pts:
return syz_open_pts(a0, a1);
case __NR_syz_fuse_mount:
return syz_fuse_mount(a0, a1, a2, a3, a4, a5);
case __NR_syz_fuseblk_mount:
return syz_fuseblk_mount(a0, a1, a2, a3, a4, a5, a6, a7);
}
}

long r[8];

int main()
{
install_segv_handler();
memset(r, -1, sizeof(r));
r[0] = execute_syscall(__NR_mmap, 0x20000000ul, 0xc000ul, 0x3ul,
0x32ul, 0xfffffffffffffffful, 0x0ul, 0, 0, 0);
NONFAILING(memcpy(
(void*)0x20004ff8,
"\x2f\x64\x65\x76\x2f\x64\x72\x69\x2f\x63\x61\x72\x64\x23\x00",
15));
r[2] = execute_syscall(__NR_syz_open_dev, 0x20004ff8ul, 0x0ul, 0x0ul,
0, 0, 0, 0, 0, 0);
r[3] = execute_syscall(__NR_ioctl, r[2], 0xc0086420ul, 0x2000a000ul,
0, 0, 0, 0, 0, 0);
if (r[3] != -1)
NONFAILING(r[4] = *(uint32_t*)0x2000a000);
NONFAILING(*(uint32_t*)0x2000aff8 = r[4]);
NONFAILING(*(uint32_t*)0x2000affc = (uint32_t)0x24);
r[7] = execute_syscall(__NR_ioctl, r[2], 0x4008642bul, 0x2000aff8ul,
0, 0, 0, 0, 0, 0);
return 0;
}

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