implement a union to pad out file_handle

Cases where name_to_handle_at is used allocated the full struct to be
MAX_HANDLE_SZ, and assigned this size to handle_bytes. This is wrong
since handle_bytes should describe the length of the flexible array
member and not the whole struct.

Define a union type which includes sufficient padding to allow
assignment of MAX_HANDLE_SZ to be correct.

Signed-off-by: Anthony G. Basile <blueness@gentoo.org>

2 files changed, 8 insertions, 4 deletions

diff --git a/src/libudev/libudev-monitor.c b/src/libudev/libudev-monitor.c
index 43fd8762da..ec3f6da91e 100644
--- a/src/libudev/libudev-monitor.c
+++ b/src/libudev/libudev-monitor.c
@@ -108,15 +108,13 @@ static struct udev_monitor *udev_monitor_new(struct udev *udev)
 
 /* we consider udev running when /dev is on devtmpfs */
 static bool udev_has_devtmpfs(struct udev *udev) {
-        struct file_handle *h;
+        union file_handle_union h = { .handle.handle_bytes = MAX_HANDLE_SZ, };
         int mount_id;
         _cleanup_fclose_ FILE *f = NULL;
         char line[LINE_MAX], *e;
         int r;
 
-        h = alloca(MAX_HANDLE_SZ);
-        h->handle_bytes = MAX_HANDLE_SZ;
-        r = name_to_handle_at(AT_FDCWD, "/dev", h, &mount_id, 0);
+        r = name_to_handle_at(AT_FDCWD, "/dev", &h.handle, &mount_id, 0);
         if (r < 0)
                 return false;
 
diff --git a/src/libudev/util.h b/src/libudev/util.h
index 6510237e1e..4efa4e062a 100644
--- a/src/libudev/util.h
+++ b/src/libudev/util.h
@@ -19,6 +19,7 @@
 
 #pragma once
 
+#include <fcntl.h>
 #include <string.h>
 #include <time.h>
 #include <stdlib.h>
@@ -300,3 +301,8 @@ static inline void qsort_safe(void *base, size_t nmemb, size_t size,
 
 int proc_cmdline(char **ret);
 int getpeercred(int fd, struct ucred *ucred);
+
+union file_handle_union {
+        struct file_handle handle;
+        char padding[sizeof(struct file_handle) + MAX_HANDLE_SZ];
+};