@@ -0,0 +1,133 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * A read that faults while copying to userspace must not hold up removal of
+ * the /proc entry. /proc/net/dev_snmp6/<dev> of a tun device is removed under
+ * RTNL when the device's file is closed.
+ */
+#define _GNU_SOURCE
+#include <errno.h>
+#include <fcntl.h>
+#include <linux/if.h>
+#include <linux/if_tun.h>
+#include <linux/userfaultfd.h>
+#include <poll.h>
+#include <pthread.h>
+#include <sched.h>
+#include <string.h>
+#include <sys/ioctl.h>
+#include <sys/mman.h>
+#include <sys/syscall.h>
+#include <unistd.h>
+
+#include "../kselftest_harness.h"
+
+#define TUN_NAME "procslow0"
+#define SNMP6_PATH "/proc/net/dev_snmp6/" TUN_NAME
+#define READ_PAGES 16
+#define TIMEOUT_MS 5000
+
+struct reader {
+ int fd;
+ char *buf;
+ size_t len;
+ ssize_t ret;
+};
+
+struct closer {
+ int tun;
+ int done;
+};
+
+static void *read_thread(void *arg)
+{
+ struct reader *r = arg;
+
+ r->ret = read(r->fd, r->buf, r->len);
+ return NULL;
+}
+
+static void *close_thread(void *arg)
+{
+ struct closer *c = arg;
+ ssize_t ret;
+
+ close(c->tun);
+ ret = write(c->done, "x", 1);
+ return (void *)ret;
+}
+
+TEST(remove_while_reader_faults)
+{
+ struct uffdio_api api = { .api = UFFD_API };
+ struct uffdio_register reg = {};
+ struct uffdio_zeropage zero = {};
+ long psz = sysconf(_SC_PAGESIZE);
+ struct ifreq ifr = {};
+ struct reader r = {};
+ struct closer c = {};
+ struct uffd_msg msg;
+ struct pollfd pfd;
+ pthread_t rt, ct;
+ int uffd, done[2];
+ char *buf;
+
+ if (unshare(CLONE_NEWNET))
+ SKIP(return, "unshare(CLONE_NEWNET): %s", strerror(errno));
+
+ c.tun = open("/dev/net/tun", O_RDWR | O_CLOEXEC);
+ if (c.tun < 0)
+ SKIP(return, "/dev/net/tun: %s", strerror(errno));
+ strncpy(ifr.ifr_name, TUN_NAME, IFNAMSIZ - 1);
+ ifr.ifr_flags = IFF_TUN | IFF_NO_PI;
+ ASSERT_EQ(ioctl(c.tun, TUNSETIFF, &ifr), 0);
+
+ r.fd = open(SNMP6_PATH, O_RDONLY | O_CLOEXEC);
+ if (r.fd < 0)
+ SKIP(return, SNMP6_PATH ": %s", strerror(errno));
+
+ uffd = syscall(__NR_userfaultfd, O_CLOEXEC | O_NONBLOCK);
+ if (uffd < 0)
+ SKIP(return, "userfaultfd: %s", strerror(errno));
+ ASSERT_EQ(ioctl(uffd, UFFDIO_API, &api), 0);
+
+ /* Only the first page of the buffer goes through userfaultfd. */
+ buf = mmap(NULL, READ_PAGES * psz, PROT_READ | PROT_WRITE,
+ MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+ ASSERT_NE(buf, MAP_FAILED);
+ reg.range.start = (unsigned long)buf;
+ reg.range.len = psz;
+ reg.mode = UFFDIO_REGISTER_MODE_MISSING;
+ ASSERT_EQ(ioctl(uffd, UFFDIO_REGISTER, ®), 0);
+
+ r.buf = buf;
+ r.len = READ_PAGES * psz;
+ ASSERT_EQ(pthread_create(&rt, NULL, read_thread, &r), 0);
+
+ /* The reader now sleeps in its copy to userspace. */
+ pfd = (struct pollfd){ .fd = uffd, .events = POLLIN };
+ ASSERT_EQ(poll(&pfd, 1, TIMEOUT_MS), 1);
+ ASSERT_EQ(read(uffd, &msg, sizeof(msg)), sizeof(msg));
+ ASSERT_EQ(msg.event, UFFD_EVENT_PAGEFAULT);
+
+ /* Closing the device removes the file that is being read. */
+ ASSERT_EQ(pipe2(done, O_CLOEXEC), 0);
+ c.done = done[1];
+ ASSERT_EQ(pthread_create(&ct, NULL, close_thread, &c), 0);
+ pfd = (struct pollfd){ .fd = done[0], .events = POLLIN };
+ EXPECT_EQ(poll(&pfd, 1, TIMEOUT_MS), 1) {
+ TH_LOG("removing " SNMP6_PATH " waited for the reader");
+ }
+
+ zero.range.start = (unsigned long)buf;
+ zero.range.len = psz;
+ ASSERT_EQ(ioctl(uffd, UFFDIO_ZEROPAGE, &zero), 0);
+ ASSERT_EQ(pthread_join(rt, NULL), 0);
+ ASSERT_EQ(pthread_join(ct, NULL), 0);
+
+ /* What was printed before the removal still arrives, then nothing. */
+ EXPECT_GT(r.ret, 0);
+ EXPECT_EQ(read(r.fd, buf, psz), -1);
+ EXPECT_EQ(errno, EIO);
+}
+
+TEST_HARNESS_MAIN