attach: file descriptor based fdinfo handling

Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

diff --git a/src/lxc/attach.c b/src/lxc/attach.c
index 8ade8db1226fcdbe0c9abc186b6125e812c3928e..e9f35d711e4c4aa55b553220de9cdb77e4384649 100644 (file)
--- a/src/lxc/attach.c
+++ b/src/lxc/attach.c
@@ -104,24 +104,22 @@ struct attach_context {
        struct lsm_ops *lsm_ops;
 };
 
-static pid_t pidfd_get_pid(int pidfd)
+static pid_t pidfd_get_pid(int dfd_init_pid, int pidfd)
 {
        __do_free char *line = NULL;
        __do_fclose FILE *f = NULL;
        size_t len = 0;
-       char path[STRLITERALLEN("/proc/self/fdinfo/") +
-                 INTTYPE_TO_STRLEN(int) + 1 ] = "/proc/self/fdinfo/";
+       char path[STRLITERALLEN("fdinfo/") + INTTYPE_TO_STRLEN(int) + 1 ] = "fdinfo/";
        int ret;
 
-       if (pidfd < 0)
-               return -EBADF;
+       if (dfd_init_pid < 0 || pidfd < 0)
+               return ret_errno(EBADF);
 
-       ret = snprintf(path + STRLITERALLEN("/proc/self/fdinfo/"),
-                       INTTYPE_TO_STRLEN(int), "%d", pidfd);
+       ret = snprintf(path + STRLITERALLEN("fdinfo/"), INTTYPE_TO_STRLEN(int), "%d", pidfd);
        if (ret < 0 || ret > (size_t)INTTYPE_TO_STRLEN(int))
                return ret_errno(EIO);
 
-       f = fopen_cloexec(path, "re");
+       f = fdopen_at(dfd_init_pid, path, "re", PROTECT_OPEN, PROTECT_LOOKUP_BENEATH);
        if (!f)
                return -errno;
 
@@ -380,21 +378,21 @@ static int get_attach_context(struct attach_context *ctx,
        ctx->container = container;
        ctx->attach_flags = options->attach_flags;
 
+       ctx->dfd_self_pid = open_at(-EBADF, "/proc/self",
+                                   PROTECT_OPATH_FILE & ~O_NOFOLLOW,
+                                   (PROTECT_LOOKUP_ABSOLUTE_WITH_SYMLINKS & ~RESOLVE_NO_XDEV), 0);
+       if (ctx->dfd_self_pid < 0)
+               return log_error_errno(-errno, errno, "Failed to open /proc/self");
+
        init_pidfd = lxc_cmd_get_init_pidfd(container->name, container->config_path);
        if (init_pidfd >= 0)
-               ctx->init_pid = pidfd_get_pid(init_pidfd);
+               ctx->init_pid = pidfd_get_pid(ctx->dfd_self_pid, init_pidfd);
        else
                ctx->init_pid = lxc_cmd_get_init_pid(container->name, container->config_path);
 
        if (ctx->init_pid < 0)
                return log_error(-1, "Failed to get init pid");
 
-       ctx->dfd_self_pid = open_at(-EBADF, "/proc/self",
-                                   PROTECT_OPATH_FILE & ~O_NOFOLLOW,
-                                   (PROTECT_LOOKUP_ABSOLUTE_WITH_SYMLINKS & ~RESOLVE_NO_XDEV), 0);
-       if (ctx->dfd_self_pid < 0)
-               return log_error_errno(-errno, errno, "Failed to open /proc/self");
-
        ret = snprintf(path, sizeof(path), "/proc/%d", ctx->init_pid);
        if (ret < 0 || ret >= sizeof(path))
                return ret_errno(EIO);