[xen stable-4.18] tools/libxs: Fix CLOEXEC handling in xs_fileno()

[patchbot@xxxxxxx]

commit 26b8ff1861a870e01456b31bf999f25df5538ebf
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Thu Jul 4 14:13:30 2024 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Thu Jul 4 14:13:30 2024 +0200

    tools/libxs: Fix CLOEXEC handling in xs_fileno()
    
    xs_fileno() opens a pipe on first use to communicate between the watch 
thread
    and the main thread.  Nothing ever sets CLOEXEC on the file descriptors.
    
    Check for the availability of the pipe2() function with configure.  Despite
    starting life as Linux-only, FreeBSD and NetBSD have gained it.
    
    When pipe2() isn't available, try our best with pipe() and set_cloexec().
    
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: Juergen Gross <jgross@xxxxxxxx>
    Acked-by: Anthony PERARD <anthony.perard@xxxxxxxxxx>
    master commit: a2ff677852f0ce05fa335e8e5682bf2ae0c916ee
    master date: 2024-07-02 10:52:59 +0100
---
 tools/config.h.in     |  3 +++
 tools/configure       | 12 ++++++++++++
 tools/configure.ac    |  2 ++
 tools/libs/store/xs.c | 16 +++++++++++++++-
 4 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/tools/config.h.in b/tools/config.h.in
index 0bb2fe08a1..50ad60fcb0 100644
--- a/tools/config.h.in
+++ b/tools/config.h.in
@@ -39,6 +39,9 @@
 /* Define to 1 if you have the <memory.h> header file. */
 #undef HAVE_MEMORY_H
 
+/* Define to 1 if you have the `pipe2' function. */
+#undef HAVE_PIPE2
+
 /* pygrub enabled */
 #undef HAVE_PYGRUB
 
diff --git a/tools/configure b/tools/configure
index 7bb935d23b..e35112b5c5 100755
--- a/tools/configure
+++ b/tools/configure
@@ -9751,6 +9751,18 @@ if test "$ax_found" = "0"; then :
 fi
 
 
+for ac_func in pipe2
+do :
+  ac_fn_c_check_func "$LINENO" "pipe2" "ac_cv_func_pipe2"
+if test "x$ac_cv_func_pipe2" = xyes; then :
+  cat >>confdefs.h <<_ACEOF
+#define HAVE_PIPE2 1
+_ACEOF
+
+fi
+done
+
+
 cat >confcache <<\_ACEOF
 # This file is a shell script that caches the results of configure
 # tests run on this system so they can be shared between configure
diff --git a/tools/configure.ac b/tools/configure.ac
index 618ef8c63f..53ac20af1e 100644
--- a/tools/configure.ac
+++ b/tools/configure.ac
@@ -543,4 +543,6 @@ AS_IF([test "x$pvshim" = "xy"], [
 
 AX_FIND_HEADER([INCLUDE_ENDIAN_H], [endian.h sys/endian.h])
 
+AC_CHECK_FUNCS([pipe2])
+
 AC_OUTPUT()
diff --git a/tools/libs/store/xs.c b/tools/libs/store/xs.c
index 11a766c508..c8845b69e2 100644
--- a/tools/libs/store/xs.c
+++ b/tools/libs/store/xs.c
@@ -190,13 +190,27 @@ static bool set_cloexec(int fd)
        return fcntl(fd, flags | FD_CLOEXEC) >= 0;
 }
 
+static int pipe_cloexec(int fds[2])
+{
+#if HAVE_PIPE2
+       return pipe2(fds, O_CLOEXEC);
+#else
+       if (pipe(fds) < 0)
+               return -1;
+       /* Best effort to set CLOEXEC.  Racy. */
+       set_cloexec(fds[0]);
+       set_cloexec(fds[1]);
+       return 0;
+#endif
+}
+
 int xs_fileno(struct xs_handle *h)
 {
        char c = 0;
 
        mutex_lock(&h->watch_mutex);
 
-       if ((h->watch_pipe[0] == -1) && (pipe(h->watch_pipe) != -1)) {
+       if ((h->watch_pipe[0] == -1) && (pipe_cloexec(h->watch_pipe) != -1)) {
                /* Kick things off if the watch list is already non-empty. */
                if (!XEN_TAILQ_EMPTY(&h->watch_list))
                        while (write(h->watch_pipe[1], &c, 1) != 1)
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.18