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#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/mman.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <errno.h>
#include <string.h>
#ifndef MADV_FREE
#define MADV_FREE 8
#endif
int anetPipe(int *fds, int read_flags, int write_flags) {
return pipe(fds);
}
int smapsGetSharedDirty(unsigned long addr) {
int ret, in_mapping = 0, val = -1;
unsigned long from, to;
char buf[64];
FILE *f;
f = fopen("/proc/self/smaps", "r");
if (!f) return -1;
while (1) {
if (!fgets(buf, sizeof(buf), f))
break;
ret = sscanf(buf, "%lx-%lx", &from, &to);
if (ret == 2)
in_mapping = from <= addr && addr < to;
if (in_mapping && !memcmp(buf, "Shared_Dirty:", 13)) {
sscanf(buf, "%*s %d", &val);
break;
}
}
fclose(f);
return val;
}
int checkLinuxMadvFreeForkBug(char **error_msg) {
int ret, pipefd[2] = { -1, -1 };
pid_t pid;
char *p = NULL, *q;
int res = 1;
long page_size = sysconf(_SC_PAGESIZE);
long map_size = 3 * page_size;
p = mmap(NULL, map_size, PROT_READ, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
if (p == MAP_FAILED) {
return 0;
}
q = p + page_size;
ret = mprotect(q, page_size, PROT_READ | PROT_WRITE);
if (ret < 0) {
res = 0;
goto exit;
}
*(volatile char*)q = 0;
ret = madvise(q, page_size, MADV_FREE);
if (ret < 0) {
if (errno == EINVAL) goto exit;
res = 0;
goto exit;
}
*(volatile char*)q = 0;
ret = anetPipe(pipefd, 0, 0);
if (ret < 0) {
res = 0;
goto exit;
}
pid = fork();
if (pid < 0) {
res = 0;
goto exit;
} else if (!pid) {
ret = smapsGetSharedDirty((unsigned long) q);
if (!ret)
res = -1;
else if (ret == -1)
res = 0;
ret = write(pipefd[1], &res, sizeof(res));
exit(0);
} else {
ret = read(pipefd[0], &res, sizeof(res));
if (ret < 0) {
res = 0;
}
waitpid(pid, NULL, 0);
}
exit:
if (pipefd[0] != -1) close(pipefd[0]);
if (pipefd[1] != -1) close(pipefd[1]);
if (p != NULL) munmap(p, map_size);
if (res == -1 && error_msg) {
*error_msg = strdup("Your kernel has a bug that could lead to data corruption during background save. Please upgrade to the latest stable kernel.");
}
return res;
}
int main() {
char *error_msg = NULL;
int result = checkLinuxMadvFreeForkBug(&error_msg);
if (result == -1) {
printf("Kernel bug detected: %s\n", error_msg);
free(error_msg);
return 1;
} else if (result == 1) {
printf("No kernel bug detected.\n");
} else {
printf("Error checking for kernel bug.\n");
}
return 0;
}
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