2018-06-25 15:23:32

by Jann Horn

Subject: [PATCH net] 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 266d07cb1c9a ("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: 266d07cb1c9a ("netfilter: nf_log: fix sleeping function calle[...]")
Signed-off-by: Jann Horn <[email protected]>
---
net/netfilter/nf_log.c | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/net/netfilter/nf_log.c b/net/netfilter/nf_log.c
index 426457047578..95b92954b896 100644
--- a/net/netfilter/nf_log.c
+++ b/net/netfilter/nf_log.c
@@ -442,14 +442,17 @@ 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;
--
2.18.0.rc2.346.g013aa6912e-goog

2018-06-26 16:18:11

by Pablo Neira Ayuso

Subject: Re: [PATCH net] netfilter: nf_log: don't hold nf_log_mutex during user access

On Mon, Jun 25, 2018 at 05:22:00PM +0200, Jann Horn wrote:
> 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 266d07cb1c9a ("netfilter: nf_log: fix
> sleeping function called from invalid context"), which changed this code
> from using rcu_read_lock() to taking nf_log_mutex.

Applied.