1 files changed, 92 insertions, 0 deletions

diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/passthrough_ll.c
index e27479f1c9..e694980a53 100644
--- a/tools/virtiofsd/passthrough_ll.c
+++ b/tools/virtiofsd/passthrough_ll.c
@@ -173,10 +173,14 @@ struct lo_data {
 
     /* An O_PATH file descriptor to /proc/self/fd/ */
     int proc_self_fd;
+    /* An O_PATH file descriptor to /proc/self/task/ */
+    int proc_self_task;
     int user_killpriv_v2, killpriv_v2;
     /* If set, virtiofsd is responsible for setting umask during creation */
     bool change_umask;
     int user_posix_acl, posix_acl;
+    /* Keeps track if /proc/<pid>/attr/fscreate should be used or not */
+    bool use_fscreate;
 };
 
 static const struct fuse_opt lo_opts[] = {
@@ -257,6 +261,72 @@ static struct lo_data *lo_data(fuse_req_t req)
 }
 
 /*
+ * Tries to figure out if /proc/<pid>/attr/fscreate is usable or not. With
+ * selinux=0, read from fscreate returns -EINVAL.
+ *
+ * TODO: Link with libselinux and use is_selinux_enabled() instead down
+ * the line. It probably will be more reliable indicator.
+ */
+static bool is_fscreate_usable(struct lo_data *lo)
+{
+    char procname[64];
+    int fscreate_fd;
+    size_t bytes_read;
+
+    sprintf(procname, "%ld/attr/fscreate", syscall(SYS_gettid));
+    fscreate_fd = openat(lo->proc_self_task, procname, O_RDWR);
+    if (fscreate_fd == -1) {
+        return false;
+    }
+
+    bytes_read = read(fscreate_fd, procname, 64);
+    close(fscreate_fd);
+    if (bytes_read == -1) {
+        return false;
+    }
+    return true;
+}
+
+/* Helpers to set/reset fscreate */
+__attribute__((unused))
+static int open_set_proc_fscreate(struct lo_data *lo, const void *ctx,
+                                  size_t ctxlen, int *fd)
+{
+    char procname[64];
+    int fscreate_fd, err = 0;
+    size_t written;
+
+    sprintf(procname, "%ld/attr/fscreate", syscall(SYS_gettid));
+    fscreate_fd = openat(lo->proc_self_task, procname, O_WRONLY);
+    err = fscreate_fd == -1 ? errno : 0;
+    if (err) {
+        return err;
+    }
+
+    written = write(fscreate_fd, ctx, ctxlen);
+    err = written == -1 ? errno : 0;
+    if (err) {
+        goto out;
+    }
+
+    *fd = fscreate_fd;
+    return 0;
+out:
+    close(fscreate_fd);
+    return err;
+}
+
+__attribute__((unused))
+static void close_reset_proc_fscreate(int fd)
+{
+    if ((write(fd, NULL, 0)) == -1) {
+        fuse_log(FUSE_LOG_WARNING, "Failed to reset fscreate. err=%d\n", errno);
+    }
+    close(fd);
+    return;
+}
+
+/*
  * Load capng's state from our saved state if the current thread
  * hadn't previously been loaded.
  * returns 0 on success
@@ -3531,6 +3601,15 @@ static void setup_namespaces(struct lo_data *lo, struct fuse_session *se)
         exit(1);
     }
 
+    /* Get the /proc/self/task descriptor */
+    lo->proc_self_task = open("/proc/self/task/", O_PATH);
+    if (lo->proc_self_task == -1) {
+        fuse_log(FUSE_LOG_ERR, "open(/proc/self/task, O_PATH): %m\n");
+        exit(1);
+    }
+
+    lo->use_fscreate = is_fscreate_usable(lo);
+
     /*
      * We only need /proc/self/fd. Prevent ".." from accessing parent
      * directories of /proc/self/fd by bind-mounting it over /proc. Since / was
@@ -3747,6 +3826,14 @@ static void setup_chroot(struct lo_data *lo)
         exit(1);
     }
 
+    lo->proc_self_task = open("/proc/self/task", O_PATH);
+    if (lo->proc_self_fd == -1) {
+        fuse_log(FUSE_LOG_ERR, "open(\"/proc/self/task\", O_PATH): %m\n");
+        exit(1);
+    }
+
+    lo->use_fscreate = is_fscreate_usable(lo);
+
     /*
      * Make the shared directory the file system root so that FUSE_OPEN
      * (lo_open()) cannot escape the shared directory by opening a symlink.
@@ -3932,6 +4019,10 @@ static void fuse_lo_data_cleanup(struct lo_data *lo)
         close(lo->proc_self_fd);
     }
 
+    if (lo->proc_self_task >= 0) {
+        close(lo->proc_self_task);
+    }
+
     if (lo->root.fd >= 0) {
         close(lo->root.fd);
     }
@@ -3959,6 +4050,7 @@ int main(int argc, char *argv[])
         .posix_lock = 0,
         .allow_direct_io = 0,
         .proc_self_fd = -1,
+        .proc_self_task = -1,
         .user_killpriv_v2 = -1,
         .user_posix_acl = -1,
     };