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tuntap(4): restrict scope of net.link.tap.user_open slightly

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net.link.tap.user_open has historically allowed non-root users to do devfs
cloning and open /dev/tap* nodes based on permissions. Loosen this up to
make it only allow users to do devfs cloning -- we no longer check it in
tunopen.

This allows tap devices to be created that can actually be opened by a user,
rather than swiftly restricting them to root because the magic sysctl has
not been set.

The sysctl has not yet been completely deprecated, because more thought is
needed for how to handle the devfs cloning case. There is not an easy
suitable replacement for the sysctl there, and more care needs to be placed
in determining whether that's OK or not.

PR:		200185
This commit is contained in:
Kyle Evans 2019-10-21 14:38:11 +00:00
parent 3ad1ce46d3
commit 3d5013337a
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=353798
2 changed files with 11 additions and 13 deletions
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9
UPDATING
View file

@ -26,6 +26,15 @@ NOTE TO PEOPLE WHO THINK THAT FreeBSD 13.x IS SLOW:
disable the most expensive debugging functionality run
"ln -s 'abort:false,junk:false' /etc/malloc.conf".)
20191021:
The net.link.tap.user_open sysctl no longer prevents user opening of
already created /dev/tapNN devices. Access is still controlled by
node permissions, just like tun devices. The net.link.tap.user_open
sysctl is now used only to allow users to perform devfs cloning of
tap devices, and the subsequent open may not succeed if the user is not
in the appropriate group. This sysctl may be deprecated/removed
completely in the future.
20191009:
mips, powerpc, and sparc64 are no longer built as part of
universe / tinderbox unless MAKE_OBSOLETE_GCC is defined. If

15
sys/net/if_tuntap.c
View file

@ -181,7 +181,7 @@ static const char vmnetname[] = "vmnet";
static MALLOC_DEFINE(M_TUN, tunname, "Tunnel Interface");
static int tundebug = 0;
static int tundclone = 1;
static int tap_allow_uopen = 0; /* allow user open() */
static int tap_allow_uopen = 0; /* allow user devfs cloning */
static int tapuponopen = 0; /* IFF_UP on open() */
static int tapdclone = 1; /* enable devfs cloning */
@ -202,7 +202,7 @@ SYSCTL_INT(_net_link_tun, OID_AUTO, devfs_cloning, CTLFLAG_RWTUN, &tundclone, 0,
static SYSCTL_NODE(_net_link, OID_AUTO, tap, CTLFLAG_RW, 0,
"Ethernet tunnel software network interface");
SYSCTL_INT(_net_link_tap, OID_AUTO, user_open, CTLFLAG_RW, &tap_allow_uopen, 0,
"Allow user to open /dev/tap (based on node permissions)");
"Enable legacy devfs interface creation for all users");
SYSCTL_INT(_net_link_tap, OID_AUTO, up_on_open, CTLFLAG_RW, &tapuponopen, 0,
"Bring interface up when /dev/tap is opened");
SYSCTL_INT(_net_link_tap, OID_AUTO, devfs_cloning, CTLFLAG_RWTUN, &tapdclone, 0,
@ -1049,17 +1049,6 @@ tunopen(struct cdev *dev, int flag, int mode, struct thread *td)
return (error); /* Shouldn't happen */
}
if ((tunflags & TUN_L2) != 0) {
/* Restrict? */
if (tap_allow_uopen == 0) {
error = priv_check(td, PRIV_NET_TAP);
if (error != 0) {
CURVNET_RESTORE();
return (error);
}
}
}
tp = dev->si_drv1;
KASSERT(tp != NULL,
("si_drv1 should have been initialized at creation"));