Ticket #651: lseek-safety-test.c

#define _XOPEN_SOURCE 500

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <errno.h>
#include <stdio.h>
#include <string.h>
#include <setjmp.h>
#include <signal.h>
#include <sys/time.h>
#include <sys/resource.h>

static sigjmp_buf jb;

static void sighandler(int signum) {
    siglongjmp(jb, signum);
}

int main(int argc, char ** argv) {
    if (argc != 2) {
        fprintf(stderr, "Usage: %s TESTFILE\n", argv[0]);
        return 1;
    }

    const char * filename = argv[1];

    int fd = open(filename, O_CREAT|O_RDWR|O_TRUNC, 0666);
    if (fd < 0) {
        perror("open failed");
        return 1;
    }

    struct rlimit rlim;
    if (getrlimit(RLIMIT_FSIZE, &rlim) < 0) {
        perror("rlimit");
    } else {
        if (rlim.rlim_cur != RLIM_INFINITY)
            printf("RLIMIT_FSIZE cur = 0x%llx\n", (long long)rlim.rlim_cur);
        if (rlim.rlim_max != RLIM_INFINITY)
            printf("RLIMIT_FSIZE max = 0x%llx\n", (long long)rlim.rlim_max);
    }

#define SHIFT (sizeof(off_t) * 8 - 2)
    volatile off_t off_t_max = (((off_t)1 << SHIFT)-1)|((off_t)1 << SHIFT);
    off_t pos = lseek(fd, off_t_max, SEEK_SET);
    if (pos == (off_t)-1) {
        perror("lseek failed");
        printf("attempted to set pos to 0x%llx\n", (long long)off_t_max);
        printf("binary chopping to find actual max:\n");
        int slo = 0;
        int shi = SHIFT + 1;
        while (shi - slo > 1) {
            int sm = slo + (shi - slo) / 2;
            off_t m = (off_t)1 << sm;
            pos = lseek(fd, m, SEEK_SET);
            if (pos == (off_t)-1) {
                printf("lseek to 0x%llx fails, errno=%d (%s)\n", (long long)m, errno, strerror(errno));
                shi = sm;
            } else {
                printf("lseek to 0x%llx works\n", (long long)m);
                slo = sm;
            }
        }

        off_t lo = (off_t)1 << slo;
        off_t hi = (off_t)1 << shi;
        while (hi - lo > 1) {
            off_t m = lo + (hi - lo) / 2;
            pos = lseek(fd, m, SEEK_SET);
            if (pos == (off_t)-1) {
                printf("lseek to 0x%llx fails, errno=%d (%s)\n", (long long)m, errno, strerror(errno));
                hi = m;
            } else {
                printf("lseek to 0x%llx works\n", (long long)m);
                lo = m;
            }
        }
        off_t_max = lo;
        printf("Max lseekable off_t = 0x%llx\n", (long long)off_t_max);
        pos = lseek(fd, off_t_max + 1, SEEK_SET);
        if (pos != -1)
            printf("Odd, +1 now works\n");
        pos = lseek(fd, off_t_max, SEEK_SET);
        if (pos == -1)
            printf("Odd, found limit now fails\n");
    }

    if (pos != off_t_max) {
        fprintf(stderr, "warning: lseek to 0x%llx actually set pos to 0x%llx\n", (long long)off_t_max, (long long)pos);
    }

    if (pwrite(fd, "hello\n", 6, 2) < 0) {
        perror("pwrite failed");
        return 1;
    }

    pos = lseek(fd, 0, SEEK_CUR);
    if (pos != off_t_max) {
        fprintf(stderr, "warning: pwrite changed file pos to 0x%llx\n", (long long)pos);
    }

    char buf[10];
    ssize_t r = pread(fd, buf, 10, 0);
    if (r < 0) {
        fprintf(stderr, "fd=%d\n", fd);
        perror("pread failed");
        return 1;
    }

    if (r != 8) {
        int i;
        fprintf(stderr, "pread() read %lld bytes, expected 8\ngot:", (long long)r);
        for (i = 0; i != (int)r; ++i) {
            fprintf(stderr, " 0x%02x", (unsigned char)buf[i]);
        }
        fprintf(stderr, "\n");
        return 1;
    }

    if (memcmp(buf, "\0\0hello\n", 8) != 0) {
        int i;
        fprintf(stderr, "pread() didn't read the expected data back\ngot:");
        for (i = 0; i != 8; ++i) {
            fprintf(stderr, " 0x%02x", (unsigned char)buf[i]);
        }
        fprintf(stderr, "\n");
        return 1;
    }

    if (sigsetjmp(jb, 1) == 0) {
        signal(SIGXFSZ, sighandler);
        r = write(fd, "", 1);
        if (r >= 0) {
            fprintf(stderr, "warning: write() succeeded, writing %lld bytes\n", (long long)r);
            pos = lseek(fd, 0, SEEK_END);
            fprintf(stderr, "lseek SEEK_END now returns 0x%llx (off_t_max was 0x%llx)\n", (long long)pos, (long long)off_t_max);
        } else {
            fprintf(stderr, "info: write() failed with errno=%d (%s)\n", errno, strerror(errno));
        }
    } else {
        fprintf(stderr, "info: write() cause SIGXFSZ to be raised\n");
    }

    pos = lseek(fd, 0, SEEK_CUR);
    if (pos != off_t_max) {
        fprintf(stderr, "warning: write changed file pos to 0x%llx\n", (long long)pos);
    }

    fprintf(stderr, "Cool, that basically worked - please report the info and/or warnings given above\n");
    return 0;
}