sethostname does not reject a too long hostname
Bruno Haible
bruno@clisp.org
Thu May 23 16:53:21 GMT 2024
The sethostname() system call is not standardized by POSIX, only by the LSB:
https://refspecs.linuxbase.org/LSB_5.0.0/LSB-Core-generic/LSB-Core-generic/baselib-sethostname-2.html
In particular, it should fail with EINVAL if
"len is negative or larger than the maximum allowed size".
In Cygwin 3.5.3, a too long hostname is not rejected.
Witness: The test program below, when run on the Cygwin 3.5.3 machines
on GitHub (under a user account that is in the Administrators group),
fails with the message "setting a too long hostname succeeded."
The implementation is in winsup/cygwin/net.cc line 773.
Bruno
====================== Test program essentially =====================
#include <assert.h>
#include <unistd.h>
/* for HOST_NAME_MAX */
#include <limits.h>
/* for strlen */
#include <string.h>
#include <errno.h>
#include <stdio.h>
#define TESTHOSTNAME "gnulib-hostname"
/* mingw and MSVC 9 lack geteuid, so setup a dummy value.
On Cygwin, geteuid() may return non-zero even for user accounts with
administrator privileges, so use a dummy value as well. */
#if defined __CYGWIN__
# define geteuid() 0
#endif
int
main (int argc, char *argv[])
{
char origname[HOST_NAME_MAX];
char newname[HOST_NAME_MAX];
char longname[HOST_NAME_MAX + 2];
int rcs, i;
/* skip the tests if we don't have root privilege. this does not
consider things like CAP_SYS_ADMIN (linux) or PRIV_SYS_ADMIN
(solaris), etc. systems without a working geteuid (mingw, MSVC
9) will always skip this test. */
if (geteuid () != 0)
{
fprintf (stderr, "Skipping test: insufficient permissions.\n");
return 77;
}
/* we want to ensure we can do a get/set/get check to ensure the
change is accepted. record the current name so it can be restored
later */
assert (gethostname (origname, sizeof (origname)) == 0);
/* try setting a valid hostname. if it fails -1/ENOSYS, we will
skip the test for long names as this is an indication we're using
the stub function that doesn't do anything on this platform. */
rcs = sethostname (TESTHOSTNAME, strlen (TESTHOSTNAME));
if (rcs != 0)
{
if (rcs == -1 && errno == ENOSYS)
{
fprintf (stderr,
"Skipping test: sethostname is not really implemented.\n");
return 77;
}
else if (rcs == -1
&& (errno == EPERM
|| errno == EACCES)) /* Cygwin */
{
fprintf (stderr, "Skipping test: insufficient permissions.\n");
return 77;
}
else
{
fprintf (stderr, "error setting valid hostname.\n");
return 1;
}
}
else
{
assert (gethostname (newname, sizeof (newname)) == 0);
/* On Windows, a hostname change becomes effective only after
a reboot. */
#if !(defined _WIN32 || defined __CYGWIN__)
/* if we don't get back what we put in, there is no need to
restore the original name as we will assume it was not
properly changed. */
if (strcmp (newname, TESTHOSTNAME) != 0)
{
fprintf (stderr, "set/get comparison failed.\n");
return 1;
}
#endif
}
/* glibc does allow setting a zero length name, so the lower bound
needs no test. validate that we are constrained by
HOST_NAME_MAX */
for (i = 0; i < (HOST_NAME_MAX + 1); i++)
longname[i] = 'a';
longname[i] = '\0';
rcs = sethostname (longname, (HOST_NAME_MAX + 1));
if (rcs != -1)
{
/* attempt to restore the original name. */
assert (sethostname (origname, strlen (origname)) == 0);
fprintf (stderr, "setting a too long hostname succeeded.\n");
return 1;
}
/* restore the original name. */
assert (sethostname (origname, strlen (origname)) == 0);
return 0;
}
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