/*
 * memfd GUP test-case
 * This tests memfd interactions with get_user_pages(). We require the
 * fuse_mnt.c program to provide a fake direct-IO FUSE mount-point for us. This
 * file-system delays _all_ reads by 1s and forces direct-IO. This means, any
 * read() on files in that file-system will pin the receive-buffer pages for at
 * least 1s via get_user_pages().
 *
 * We use this trick to race ADD_SEALS against a write on a memfd object. The
 * ADD_SEALS must fail if the memfd pages are still pinned. Note that we use
 * the read() syscall with our memory-mapped memfd object as receive buffer to
 * force the kernel to write into our memfd object.
 */

#define _GNU_SOURCE
#define __EXPORTED_HEADERS__

#include <errno.h>
#include <inttypes.h>
#include <limits.h>
#include <linux/falloc.h>
#include <linux/fcntl.h>
#include <linux/memfd.h>
#include <sched.h>
#include <stdio.h>
#include <stdlib.h>
#include <signal.h>
#include <string.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <sys/syscall.h>
#include <sys/wait.h>
#include <unistd.h>

#define MFD_DEF_SIZE 8192
#define STACK_SIZE 65535

static int sys_memfd_create(const char *name,
                            unsigned int flags)
{
        return syscall(__NR_memfd_create, name, flags);
}

static int mfd_assert_new(const char *name, loff_t sz, unsigned int flags)
{
        int r, fd;

        fd = sys_memfd_create(name, flags);
        if (fd < 0) {
                printf("memfd_create(\"%s\", %u) failed: %m\n",
                       name, flags);
                abort();
        }

        r = ftruncate(fd, sz);
        if (r < 0) {
                printf("ftruncate(%llu) failed: %m\n", (unsigned long long)sz);
                abort();
        }

        return fd;
}

static __u64 mfd_assert_get_seals(int fd)
{
        long r;

        r = fcntl(fd, F_GET_SEALS);
        if (r < 0) {
                printf("GET_SEALS(%d) failed: %m\n", fd);
                abort();
        }

        return r;
}

static void mfd_assert_has_seals(int fd, __u64 seals)
{
        __u64 s;

        s = mfd_assert_get_seals(fd);
        if (s != seals) {
                printf("%llu != %llu = GET_SEALS(%d)\n",
                       (unsigned long long)seals, (unsigned long long)s, fd);
                abort();
        }
}

static void mfd_assert_add_seals(int fd, __u64 seals)
{
        long r;
        __u64 s;

        s = mfd_assert_get_seals(fd);
        r = fcntl(fd, F_ADD_SEALS, seals);
        if (r < 0) {
                printf("ADD_SEALS(%d, %llu -> %llu) failed: %m\n",
                       fd, (unsigned long long)s, (unsigned long long)seals);
                abort();
        }
}

static int mfd_busy_add_seals(int fd, __u64 seals)
{
        long r;
        __u64 s;

        r = fcntl(fd, F_GET_SEALS);
        if (r < 0)
                s = 0;
        else
                s = r;

        r = fcntl(fd, F_ADD_SEALS, seals);
        if (r < 0 && errno != EBUSY) {
                printf("ADD_SEALS(%d, %llu -> %llu) didn't fail as expected with EBUSY: %m\n",
                       fd, (unsigned long long)s, (unsigned long long)seals);
                abort();
        }

        return r;
}

static void *mfd_assert_mmap_shared(int fd)
{
        void *p;

        p = mmap(NULL,
                 MFD_DEF_SIZE,
                 PROT_READ | PROT_WRITE,
                 MAP_SHARED,
                 fd,
                 0);
        if (p == MAP_FAILED) {
                printf("mmap() failed: %m\n");
                abort();
        }

        return p;
}

static void *mfd_assert_mmap_private(int fd)
{
        void *p;

        p = mmap(NULL,
                 MFD_DEF_SIZE,
                 PROT_READ | PROT_WRITE,
                 MAP_PRIVATE,
                 fd,
                 0);
        if (p == MAP_FAILED) {
                printf("mmap() failed: %m\n");
                abort();
        }

        return p;
}

static int global_mfd = -1;
static void *global_p = NULL;

static int sealing_thread_fn(void *arg)
{
        int sig, r;

        /*
         * This thread first waits 200ms so any pending operation in the parent
         * is correctly started. After that, it tries to seal @global_mfd as
         * SEAL_WRITE. This _must_ fail as the parent thread has a read() into
         * that memory mapped object still ongoing.
         * We then wait one more second and try sealing again. This time it
         * must succeed as there shouldn't be anyone else pinning the pages.
         */

        /* wait 200ms for FUSE-request to be active */
        usleep(200000);

        /* unmount mapping before sealing to avoid i_mmap_writable failures */
        munmap(global_p, MFD_DEF_SIZE);

        /* Try sealing the global file; expect EBUSY or success. Current
         * kernels will never succeed, but in the future, kernels might
         * implement page-replacements or other fancy ways to avoid racing
         * writes. */
        r = mfd_busy_add_seals(global_mfd, F_SEAL_WRITE);
        if (r >= 0) {
                printf("HURRAY! This kernel fixed GUP races!\n");
        } else {
                /* wait 1s more so the FUSE-request is done */
                sleep(1);

                /* try sealing the global file again */
                mfd_assert_add_seals(global_mfd, F_SEAL_WRITE);
        }

        return 0;
}

static pid_t spawn_sealing_thread(void)
{
        uint8_t *stack;
        pid_t pid;

        stack = malloc(STACK_SIZE);
        if (!stack) {
                printf("malloc(STACK_SIZE) failed: %m\n");
                abort();
        }

        pid = clone(sealing_thread_fn,
                    stack + STACK_SIZE,
                    SIGCHLD | CLONE_FILES | CLONE_FS | CLONE_VM,
                    NULL);
        if (pid < 0) {
                printf("clone() failed: %m\n");
                abort();
        }

        return pid;
}

static void join_sealing_thread(pid_t pid)
{
        waitpid(pid, NULL, 0);
}

int main(int argc, char **argv)
{
        static const char zero[MFD_DEF_SIZE];
        int fd, mfd, r;
        void *p;
        int was_sealed;
        pid_t pid;

        if (argc < 2) {
                printf("error: please pass path to file in fuse_mnt mount-point\n");
                abort();
        }

        /* open FUSE memfd file for GUP testing */
        printf("opening: %s\n", argv[1]);
        fd = open(argv[1], O_RDONLY | O_CLOEXEC);
        if (fd < 0) {
                printf("cannot open(\"%s\"): %m\n", argv[1]);
                abort();
        }

        /* create new memfd-object */
        mfd = mfd_assert_new("kern_memfd_fuse",
                             MFD_DEF_SIZE,
                             MFD_CLOEXEC | MFD_ALLOW_SEALING);

        /* mmap memfd-object for writing */
        p = mfd_assert_mmap_shared(mfd);

        /* pass mfd+mapping to a separate sealing-thread which tries to seal
         * the memfd objects with SEAL_WRITE while we write into it */
        global_mfd = mfd;
        global_p = p;
        pid = spawn_sealing_thread();

        /* Use read() on the FUSE file to read into our memory-mapped memfd
         * object. This races the other thread which tries to seal the
         * memfd-object.
         * If @fd is on the memfd-fake-FUSE-FS, the read() is delayed by 1s.
         * This guarantees that the receive-buffer is pinned for 1s until the
         * data is written into it. The racing ADD_SEALS should thus fail as
         * the pages are still pinned. */
        r = read(fd, p, MFD_DEF_SIZE);
        if (r < 0) {
                printf("read() failed: %m\n");
                abort();
        } else if (!r) {
                printf("unexpected EOF on read()\n");
                abort();
        }

        was_sealed = mfd_assert_get_seals(mfd) & F_SEAL_WRITE;

        /* Wait for sealing-thread to finish and verify that it
         * successfully sealed the file after the second try. */
        join_sealing_thread(pid);
        mfd_assert_has_seals(mfd, F_SEAL_WRITE);

        /* *IF* the memfd-object was sealed at the time our read() returned,
         * then the kernel did a page-replacement or canceled the read() (or
         * whatever magic it did..). In that case, the memfd object is still
         * all zero.
         * In case the memfd-object was *not* sealed, the read() was successfull
         * and the memfd object must *not* be all zero.
         * Note that in real scenarios, there might be a mixture of both, but
         * in this test-cases, we have explicit 200ms delays which should be
         * enough to avoid any in-flight writes. */

        p = mfd_assert_mmap_private(mfd);
        if (was_sealed && memcmp(p, zero, MFD_DEF_SIZE)) {
                printf("memfd sealed during read() but data not discarded\n");
                abort();
        } else if (!was_sealed && !memcmp(p, zero, MFD_DEF_SIZE)) {
                printf("memfd sealed after read() but data discarded\n");
                abort();
        }

        close(mfd);
        close(fd);

        printf("fuse: DONE\n");

        return 0;
}