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

[patchbot@xxxxxxx]

commit d1b3bbb46402af77089906a97c413c14ed1740d2
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Thu Jul 4 14:13:10 2024 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Thu Jul 4 14:13:10 2024 +0200

    tools/libxs: Fix CLOEXEC handling in get_dev()
    
    Move the O_CLOEXEC compatibility outside of an #ifdef USE_PTHREAD block.
    
    Introduce set_cloexec() to wrap fcntl() setting FD_CLOEXEC.  It will be 
reused
    for other CLOEXEC fixes too.
    
    Use set_cloexec() when O_CLOEXEC isn't available as a best-effort fallback.
    
    Fixes: f4f2f3402b2f ("tools/libxs: Open /dev/xen/xenbus fds as O_CLOEXEC")
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: Juergen Gross <jgross@xxxxxxxx>
    Acked-by: Anthony PERARD <anthony.perard@xxxxxxxxxx>
    master commit: bf7c1464706adfa903f1e7d59383d042c3a88e39
    master date: 2024-07-02 10:51:06 +0100
---
 tools/libs/store/xs.c | 38 ++++++++++++++++++++++++++++++++------
 1 file changed, 32 insertions(+), 6 deletions(-)

diff --git a/tools/libs/store/xs.c b/tools/libs/store/xs.c
index 1498515073..037e79d98b 100644
--- a/tools/libs/store/xs.c
+++ b/tools/libs/store/xs.c
@@ -40,6 +40,10 @@
 #include <xentoolcore_internal.h>
 #include <xen_list.h>
 
+#ifndef O_CLOEXEC
+#define O_CLOEXEC 0
+#endif
+
 struct xs_stored_msg {
        XEN_TAILQ_ENTRY(struct xs_stored_msg) list;
        struct xsd_sockmsg hdr;
@@ -54,10 +58,6 @@ struct xs_stored_msg {
 #include <dlfcn.h>
 #endif
 
-#ifndef O_CLOEXEC
-#define O_CLOEXEC 0
-#endif
-
 struct xs_handle {
        /* Communications channel to xenstore daemon. */
        int fd;
@@ -176,6 +176,16 @@ static bool setnonblock(int fd, int nonblock) {
        return true;
 }
 
+static bool set_cloexec(int fd)
+{
+       int flags = fcntl(fd, F_GETFL);
+
+       if (flags < 0)
+               return false;
+
+       return fcntl(fd, flags | FD_CLOEXEC) >= 0;
+}
+
 int xs_fileno(struct xs_handle *h)
 {
        char c = 0;
@@ -230,8 +240,24 @@ error:
 
 static int get_dev(const char *connect_to)
 {
-       /* We cannot open read-only because requests are writes */
-       return open(connect_to, O_RDWR | O_CLOEXEC);
+       int fd, saved_errno;
+
+       fd = open(connect_to, O_RDWR | O_CLOEXEC);
+       if (fd < 0)
+               return -1;
+
+       /* Compat for non-O_CLOEXEC environments.  Racy. */
+       if (!O_CLOEXEC && !set_cloexec(fd))
+               goto error;
+
+       return fd;
+
+error:
+       saved_errno = errno;
+       close(fd);
+       errno = saved_errno;
+
+       return -1;
 }
 
 static int all_restrict_cb(Xentoolcore__Active_Handle *ah, domid_t domid) {
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.18