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drop_monitor/genetlink: use proper genetlink multicast APIs

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The drop monitor code is abusing the genetlink API and is
statically using the generic netlink multicast group 1, even
if that group belongs to somebody else (which it invariably
will, since it's not reserved.)

Make the drop monitor code use the proper APIs to reserve a
group ID, but also reserve the group id 1 in generic netlink
code to preserve the userspace API. Since drop monitor can
be a module, don't clear the bit for it on unregistration.

Acked-by: Neil Horman <[email protected]>
Signed-off-by: Johannes Berg <[email protected]>
Signed-off-by: David S. Miller <[email protected]>
This commit is contained in:
Johannes Berg 2013-11-19 15:19:32 +01:00 • committed by David S. Miller
commit e5dcecba01
2 changed files with 22 additions and 4 deletions
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13
net/netlink/genetlink.c
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@ -65,8 +65,12 @@ static struct list_head family_ht[GENL_FAM_TAB_SIZE];
* To avoid an allocation at boot of just one unsigned long,
* declare it global instead.
* Bit 0 is marked as already used since group 0 is invalid.
* Bit 1 is marked as already used since the drop-monitor code
* abuses the API and thinks it can statically use group 1.
* That group will typically conflict with other groups that
* any proper users use.
*/
static unsigned long mc_group_start = 0x1;
static unsigned long mc_group_start = 0x3;
static unsigned long *mc_groups = &mc_group_start;
static unsigned long mc_groups_longs = 1;
@ -160,9 +164,11 @@ int genl_register_mc_group(struct genl_family *family,
genl_lock_all();
/* special-case our own group */
/* special-case our own group and hacks */
if (grp == &notify_grp)
id = GENL_ID_CTRL;
else if (strcmp(family->name, "NET_DM") == 0)
id = 1;
else
id = find_first_zero_bit(mc_groups,
mc_groups_longs * BITS_PER_LONG);
@ -245,7 +251,8 @@ static void __genl_unregister_mc_group(struct genl_family *family,
rcu_read_unlock();
netlink_table_ungrab();
clear_bit(grp->id, mc_groups);
if (grp->id != 1)
clear_bit(grp->id, mc_groups);
list_del(&grp->list);
genl_ctrl_event(CTRL_CMD_DELMCAST_GRP, grp);
grp->id = 0;