Commit ce00bf07 authored Jun 25, 2018 by Jann Horn Committed by Pablo Neira Ayuso Jun 26, 2018

netfilter: nf_log: don't hold nf_log_mutex during user access

The old code would indefinitely block other users of nf_log_mutex if
a userspace access in proc_dostring() blocked e.g. due to a userfaultfd
region. Fix it by moving proc_dostring() out of the locked region.

This is a followup to commit 266d07cb ("netfilter: nf_log: fix
sleeping function called from invalid context"), which changed this code
from using rcu_read_lock() to taking nf_log_mutex.

Fixes: 266d07cb ("netfilter: nf_log: fix sleeping function calle[...]")
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

parent dffd22ae

net/netfilter/nf_log.c

+6 −3

Original line number	Diff line number	Diff line
		@@ -446,14 +446,17 @@ static int nf_log_proc_dostring(struct ctl_table *table, int write,
		rcu_assign_pointer(net->nf.nf_loggers[tindex], logger);
		mutex_unlock(&nf_log_mutex);
		} else {
		struct ctl_table tmp = *table;

		tmp.data = buf;
		mutex_lock(&nf_log_mutex);
		logger = nft_log_dereference(net->nf.nf_loggers[tindex]);
		if (!logger)
		table->data = "NONE";
		strlcpy(buf, "NONE", sizeof(buf));
		else
		table->data = logger->name;
		r = proc_dostring(table, write, buffer, lenp, ppos);
		strlcpy(buf, logger->name, sizeof(buf));
		mutex_unlock(&nf_log_mutex);
		r = proc_dostring(&tmp, write, buffer, lenp, ppos);
		}

		return r;

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