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

commit ce00bf07cc95a57cd20b208e02b3c2604e532ae8 upstream.

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 266d07cb1c ("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: 266d07cb1c ("netfilter: nf_log: fix sleeping function calle[...]")
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Jann Horn 2018-06-25 17:22:00 +02:00 committed by syphyr
parent 69581c58e7
commit bdcf8f96c2
1 changed files with 6 additions and 3 deletions
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9
net/netfilter/nf_log.c
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@ -274,15 +274,18 @@ static int nf_log_proc_dostring(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 = rcu_dereference_protected(net->nf.nf_loggers[tindex],
lockdep_is_held(&nf_log_mutex));
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;