Messages in this thread |  | | From | Saeed Mirzamohammadi <> | | Subject | Re: [PATCH 1/1] video: fbdev: fix divide error in fbcon_switch | | Date | Wed, 21 Oct 2020 17:33:31 -0700 |
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Attached the Syzkaller C reproducer.
#define _GNU_SOURCE
#include <dirent.h> #include <endian.h> #include <errno.h> #include <fcntl.h> #include <pthread.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>
#include <linux/futex.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 void thread_start(void* (*fn)(void*), void* arg) { pthread_t th; pthread_attr_t attr; pthread_attr_init(&attr); pthread_attr_setstacksize(&attr, 128 << 10); int i; for (i = 0; i < 100; i++) { if (pthread_create(&th, &attr, fn, arg) == 0) { pthread_attr_destroy(&attr); return; } if (errno == EAGAIN) { usleep(50); continue; } break; } exit(1); }
typedef struct { int state; } event_t;
static void event_init(event_t* ev) { ev->state = 0; }
static void event_reset(event_t* ev) { ev->state = 0; }
static void event_set(event_t* ev) { if (ev->state) exit(1); __atomic_store_n(&ev->state, 1, __ATOMIC_RELEASE); syscall(SYS_futex, &ev->state, FUTEX_WAKE | FUTEX_PRIVATE_FLAG, 1000000); }
static void event_wait(event_t* ev) { while (!__atomic_load_n(&ev->state, __ATOMIC_ACQUIRE)) syscall(SYS_futex, &ev->state, FUTEX_WAIT | FUTEX_PRIVATE_FLAG, 0, 0); }
static int event_isset(event_t* ev) { return __atomic_load_n(&ev->state, __ATOMIC_ACQUIRE); }
static int event_timedwait(event_t* ev, uint64_t timeout) { uint64_t start = current_time_ms(); uint64_t now = start; for (;;) { uint64_t remain = timeout - (now - start); struct timespec ts; ts.tv_sec = remain / 1000; ts.tv_nsec = (remain % 1000) * 1000 * 1000; syscall(SYS_futex, &ev->state, FUTEX_WAIT | FUTEX_PRIVATE_FLAG, 0, &ts); if (__atomic_load_n(&ev->state, __ATOMIC_RELAXED)) return 1; now = current_time_ms(); if (now - start > timeout) return 0; } }
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 long syz_open_dev(volatile long a0, volatile long a1, volatile long 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) - 1); buf[sizeof(buf) - 1] = 0; while ((hash = strchr(buf, '#'))) { *hash = '0' + (char)(a1 % 10); a1 /= 10; } return open(buf, a2, 0); } }
static void kill_and_wait(int pid, int* status) { kill(-pid, SIGKILL); kill(pid, SIGKILL); int i; for (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"); }
struct thread_t { int created, call; event_t ready, done; };
static struct thread_t threads[16]; static void execute_call(int call); static int running;
static void* thr(void* arg) { struct thread_t* th = (struct thread_t*)arg; for (;;) { event_wait(&th->ready); event_reset(&th->ready); execute_call(th->call); __atomic_fetch_sub(&running, 1, __ATOMIC_RELAXED); event_set(&th->done); } return 0; }
static void execute_one(void) { int i, call, thread; int collide = 0; again: for (call = 0; call < 6; call++) { for (thread = 0; thread < (int)(sizeof(threads) / sizeof(threads[0])); thread++) { struct thread_t* th = &threads[thread]; if (!th->created) { th->created = 1; event_init(&th->ready); event_init(&th->done); event_set(&th->done); thread_start(thr, th); } if (!event_isset(&th->done)) continue; event_reset(&th->done); th->call = call; __atomic_fetch_add(&running, 1, __ATOMIC_RELAXED); event_set(&th->ready); if (collide && (call % 2) == 0) break; event_timedwait(&th->done, 45); break; } } for (i = 0; i < 100 && __atomic_load_n(&running, __ATOMIC_RELAXED); i++) sleep_ms(1); if (!collide) { collide = 1; goto again; } }
static void execute_one(void);
#define WAIT_FLAGS __WALL
static void loop(void) { int iter; for (iter = 0;; 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 < 5 * 1000) continue; kill_and_wait(pid, &status); break; } } }
uint64_t r[2] = {0xffffffffffffffff, 0xffffffffffffffff};
void execute_call(int call) { intptr_t res; switch (call) { case 0: memcpy((void*)0x20000000, "/dev/fb0\000", 9); res = syscall(__NR_openat, 0xffffffffffffff9cul, 0x20000000ul, 0ul, 0ul); if (res != -1) r[0] = res; break; case 1: *(uint32_t*)0x20000100 = 0; *(uint32_t*)0x20000104 = 0x10; *(uint32_t*)0x20000108 = 0; *(uint32_t*)0x2000010c = 0; *(uint32_t*)0x20000110 = 0; *(uint32_t*)0x20000114 = 0; *(uint32_t*)0x20000118 = 0; *(uint32_t*)0x2000011c = 0; *(uint32_t*)0x20000120 = 0; *(uint32_t*)0x20000124 = 0; *(uint32_t*)0x20000128 = 0; *(uint32_t*)0x2000012c = 0; *(uint32_t*)0x20000130 = 0; *(uint32_t*)0x20000134 = 0; *(uint32_t*)0x20000138 = 0; *(uint32_t*)0x2000013c = 0; *(uint32_t*)0x20000140 = 0; *(uint32_t*)0x20000144 = 0; *(uint32_t*)0x20000148 = 0; *(uint32_t*)0x2000014c = 0; *(uint32_t*)0x20000150 = 0; *(uint32_t*)0x20000154 = 0; *(uint32_t*)0x20000158 = 0; *(uint32_t*)0x2000015c = 0; *(uint32_t*)0x20000160 = 0; *(uint32_t*)0x20000164 = 0; *(uint32_t*)0x20000168 = 0; *(uint32_t*)0x2000016c = 0; *(uint32_t*)0x20000170 = 0; *(uint32_t*)0x20000174 = 0; *(uint32_t*)0x20000178 = 0; *(uint32_t*)0x2000017c = 0; *(uint32_t*)0x20000180 = 0; *(uint32_t*)0x20000184 = 0; *(uint32_t*)0x20000188 = 0; *(uint32_t*)0x2000018c = 0; *(uint32_t*)0x20000190 = 0; *(uint32_t*)0x20000194 = 0; *(uint32_t*)0x20000198 = 0; *(uint32_t*)0x2000019c = 0; syscall(__NR_ioctl, r[0], 0x4601ul, 0x20000100ul); break; case 2: syscall(__NR_socket, 0xaul, 3ul, 0x3aul); break; case 3: res = syz_open_dev(0xc, 4, 0x14); if (res != -1) r[1] = res; break; case 4: syscall(__NR_ioctl, r[1], 0x5437ul, 0ul); break; case 5: syscall(__NR_ioctl, r[1], 0x5606ul, 8ul); break; }
} int main(void) { syscall(__NR_mmap, 0x20000000ul, 0x1000000ul, 3ul, 0x32ul, -1, 0); loop(); return 0; }
> On Oct 21, 2020, at 4:57 PM, saeed.mirzamohammadi@oracle.com wrote: > > From: Saeed Mirzamohammadi <saeed.mirzamohammadi@oracle.com> > > This patch fixes the issue due to: > > [ 89.572883] divide_error: 0000 [#1] SMP KASAN PTI > [ 89.572897] CPU: 3 PID: 16083 Comm: repro Not tainted 5.9.0-rc7.20200930.rc1.allarch-19-g3e32d0d.syzk #5 > [ 89.572902] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 0.5.1 01/01/2011 > [ 89.572934] RIP: 0010:cirrusfb_check_var+0x84/0x1260 > > The error happens when the pixels value is calculated before performing the sanity checks on bits_per_pixel. > A bits_per_pixel set to zero causes divide by zero error. > > This patch moves the calculation after the sanity check. > > Signed-off-by: Saeed Mirzamohammadi <saeed.mirzamohammadi@oracle.com> > Tested-by: Saeed Mirzamohammadi <saeed.mirzamohammadi@oracle.com> > --- > drivers/video/fbdev/cirrusfb.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/drivers/video/fbdev/cirrusfb.c b/drivers/video/fbdev/cirrusfb.c > index 15a9ee7cd734..a7749101b094 100644 > --- a/drivers/video/fbdev/cirrusfb.c > +++ b/drivers/video/fbdev/cirrusfb.c > @@ -531,7 +531,7 @@ static int cirrusfb_check_var(struct fb_var_screeninfo *var, > { > int yres; > /* memory size in pixels */ > - unsigned pixels = info->screen_size * 8 / var->bits_per_pixel; > + unsigned int pixels; > struct cirrusfb_info *cinfo = info->par; > > switch (var->bits_per_pixel) { > @@ -573,6 +573,7 @@ static int cirrusfb_check_var(struct fb_var_screeninfo *var, > return -EINVAL; > } > > + pixels = info->screen_size * 8 / var->bits_per_pixel; > if (var->xres_virtual < var->xres) > var->xres_virtual = var->xres; > /* use highest possible virtual resolution */ > -- > 2.27.0 >
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