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socket-util-unix: Fix umask race in bind_unix_socket().

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The umask is a process-wide value, so bind_unix_socket() races with file
creation in other Open vSwitch threads.  This fixes the race.

The workaround for non-Linux systems is not ideal, but I do not know any
other general solution.  I tested the workaround only on Linux.

CC: YAMAMOTO Takashi <yamamoto@valinux.co.jp>
Signed-off-by: Ben Pfaff <blp@nicira.com>
Acked-by: Flavio Leitner <fbl@redhat.com>
This commit is contained in:
Ben Pfaff
2014-08-07 16:25:05 -07:00
parent c38fe63e93
commit 2d5cfef825
1 changed files with 39 additions and 5 deletions
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44
lib/socket-util-unix.c
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@@ -23,6 +23,7 @@
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/un.h>
#include <sys/wait.h>
#include <unistd.h>
#include "fatal-signal.h"
#include "random.h"
@@ -261,11 +262,44 @@ free_sockaddr_un(int dirfd, const char *linkname)
static int
bind_unix_socket(int fd, struct sockaddr *sun, socklen_t sun_len)
{
/* According to _Unix Network Programming_, umask should affect bind(). */
mode_t old_umask = umask(0077);
int error = bind(fd, sun, sun_len) ? errno : 0;
umask(old_umask);
return error;
const mode_t mode = 0700;
if (LINUX) {
/* On Linux, the fd's permissions become the file's permissions.
* fchmod() does not affect other files, like umask() does. */
if (fchmod(fd, mode)) {
return errno;
}
/* Must be after fchmod(). */
if (bind(fd, sun, sun_len)) {
return errno;
}
return 0;
} else {
/* On FreeBSD and NetBSD, only the umask affects permissions. The
* umask is process-wide rather than thread-specific, so we have to use
* a subprocess for safety. */
pid_t pid = fork();
if (!pid) {
umask(mode ^ 0777);
_exit(bind(fd, sun, sun_len) ? errno : 0);
} else if (pid > 0) {
int status;
int error;
do {
error = waitpid(pid, &status, 0) < 0 ? errno : 0;
} while (error == EINTR);
return (error ? error
: WIFEXITED(status) ? WEXITSTATUS(status)
: WIFSIGNALED(status) ? EINTR
: ECHILD /* WTF? */);
} else {
return errno;
}
}
}
/* Creates a Unix domain socket in the given 'style' (either SOCK_DGRAM or