rexec: try sendfile() fallback to fd_to_fd()

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

diff --git a/src/lxc/rexec.c b/src/lxc/rexec.c
index 58f3ff48618c98c5c77a9d1a1c9d2ab3735dd52e..39399826f203013d5d67797c7dd30f287eaf58b5 100644 (file)
--- a/src/lxc/rexec.c
+++ b/src/lxc/rexec.c
@@ -105,8 +105,11 @@ static int is_memfd(void)
 
 static void lxc_rexec_as_memfd(char **argv, char **envp, const char *memfd_name)
 {
-       __do_close_prot_errno int fd = -EBADF, memfd = -EBADF, tmpfd = -EBADF;
+       __do_close_prot_errno int execfd = -EBADF, fd = -EBADF, memfd = -EBADF,
+                                 tmpfd = -EBADF;
        int ret;
+       ssize_t bytes_sent = 0;
+       struct stat st = {0};
 
        memfd = memfd_create(memfd_name, MFD_ALLOW_SEALING | MFD_CLOEXEC);
        if (memfd < 0) {
@@ -131,35 +134,35 @@ static void lxc_rexec_as_memfd(char **argv, char **envp, const char *memfd_name)
                return;
 
        /* sendfile() handles up to 2GB. */
-       if (memfd >= 0) {
-               ssize_t bytes_sent = 0;
-               struct stat st = {0};
+       ret = fstat(fd, &st);
+       if (ret)
+               return;
 
-               ret = fstat(fd, &st);
-               if (ret)
-                       return;
+       while (bytes_sent < st.st_size) {
+               ssize_t sent;
 
-               while (bytes_sent < st.st_size) {
-                       ssize_t sent;
-                       sent = lxc_sendfile_nointr(memfd, fd, NULL,
-                                                  st.st_size - bytes_sent);
-                       if (sent < 0)
-                               return;
-                       bytes_sent += sent;
+               sent = lxc_sendfile_nointr(memfd >= 0 ? memfd : tmpfd, fd, NULL,
+                                          st.st_size - bytes_sent);
+               if (sent < 0) {
+                       /* Fallback to shoveling data between kernel- and
+                        * userspace.
+                        */
+                       lseek(fd, 0, SEEK_SET);
+                       if (fd_to_fd(fd, memfd >= 0 ? memfd : tmpfd))
+                               break;
+
+                       return;
                }
-       } else if (fd_to_fd(fd, tmpfd)) {
-               return;
+               bytes_sent += sent;
        }
-
        close_prot_errno_disarm(fd);
 
-       if (memfd >= 0 && fcntl(memfd, F_ADD_SEALS, LXC_MEMFD_REXEC_SEALS))
-               return;
-
        if (memfd >= 0) {
-               fexecve(memfd, argv, envp);
+               if (fcntl(memfd, F_ADD_SEALS, LXC_MEMFD_REXEC_SEALS))
+                       return;
+
+               execfd = memfd;
        } else {
-               __do_close_prot_errno int execfd = -EBADF;
                char procfd[LXC_PROC_PID_FD_LEN];
 
                ret = snprintf(procfd, sizeof(procfd), "/proc/self/fd/%d", tmpfd);
@@ -168,11 +171,12 @@ static void lxc_rexec_as_memfd(char **argv, char **envp, const char *memfd_name)
 
                execfd = open(procfd, O_PATH | O_CLOEXEC);
                close_prot_errno_disarm(tmpfd);
-               if (execfd < 0)
-                       return;
 
-               fexecve(execfd, argv, envp);
        }
+       if (execfd < 0)
+               return;
+
+       fexecve(execfd, argv, envp);
 }
 
 /*