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From:   Kuniyuki Iwashima <kuniyu@amazon.com>
To:     "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        Luis Chamberlain <mcgrof@kernel.org>,
        Kees Cook <keescook@chromium.org>,
        Iurii Zaikin <yzaikin@google.com>
CC:     Kuniyuki Iwashima <kuniyu@amazon.com>,
        Kuniyuki Iwashima <kuni1840@gmail.com>,
        <netdev@vger.kernel.org>, <linux-kernel@vger.kernel.org>
Subject: [PATCH v1 net 05/16] sysctl: Add proc_dointvec_minmax_lockless().
Date:   Tue, 5 Jul 2022 22:21:19 -0700
Message-ID: <20220706052130.16368-6-kuniyu@amazon.com>
In-Reply-To: <20220706052130.16368-1-kuniyu@amazon.com>
References: <20220706052130.16368-1-kuniyu@amazon.com>
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A sysctl variable is accessed concurrently, and there is always a chance of
data-race.  So, all readers and writers need some basic protection to avoid
load/store-tearing.

This patch changes proc_dointvec_minmax() to use READ_ONCE()/WRITE_ONCE()
internally to fix a data-race on the sysctl side.  For now,
proc_dointvec_minmax() itself is tolerant to a data-race, but we still need
to add annotations on the other subsystem's side.

In case we miss such fixes, this patch converts proc_dointvec_minmax() to a
wrapper of proc_dointvec_minmax_lockless().  When we fix a data-race in the
other subsystem, we can explicitly set it as a handler.

Also, this patch removes proc_dointvec_minmax()'s document and adds
proc_dointvec_minmax_lockless()'s one so that no one will use
proc_dointvec_minmax() anymore.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
---
 include/linux/sysctl.h |  1 +
 kernel/sysctl.c        | 19 +++++++++++++++----
 2 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
index 770ee1833c25..7f91cc625d56 100644
--- a/include/linux/sysctl.h
+++ b/include/linux/sysctl.h
@@ -86,6 +86,7 @@ PROC_HANDLER(proc_do_static_key);
 PROC_HANDLER(proc_dobool_lockless);
 PROC_HANDLER(proc_dointvec_lockless);
 PROC_HANDLER(proc_douintvec_lockless);
+PROC_HANDLER(proc_dointvec_minmax_lockless);
 
 /*
  * Register a set of sysctl names by calling register_sysctl_table
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index be8a7d912180..aead731ae74b 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -879,14 +879,16 @@ static int do_proc_dointvec_minmax_conv(bool *negp, unsigned long *lvalp,
 		if ((param->min && *param->min > tmp) ||
 		    (param->max && *param->max < tmp))
 			return -EINVAL;
-		*valp = tmp;
+
+		WRITE_ONCE(*valp, tmp);
 	}
 
 	return 0;
 }
 
 /**
- * proc_dointvec_minmax - read a vector of integers with min/max values
+ * proc_dointvec_minmax_lockless - read/write a vector of integers with
+ * min/max values locklessly
  * @table: the sysctl table
  * @write: %TRUE if this is a write to the sysctl file
  * @buffer: the user buffer
@@ -901,8 +903,8 @@ static int do_proc_dointvec_minmax_conv(bool *negp, unsigned long *lvalp,
  *
  * Returns 0 on success or -EINVAL on write when the range check fails.
  */
-int proc_dointvec_minmax(struct ctl_table *table, int write,
-		  void *buffer, size_t *lenp, loff_t *ppos)
+int proc_dointvec_minmax_lockless(struct ctl_table *table, int write,
+				  void *buffer, size_t *lenp, loff_t *ppos)
 {
 	struct do_proc_dointvec_minmax_conv_param param = {
 		.min = (int *) table->extra1,
@@ -912,6 +914,13 @@ int proc_dointvec_minmax(struct ctl_table *table, int write,
 				do_proc_dointvec_minmax_conv, &param);
 }
 
+int proc_dointvec_minmax(struct ctl_table *table, int write,
+			 void *buffer, size_t *lenp, loff_t *ppos)
+{
+	return proc_dointvec_minmax_lockless(table, write, buffer,
+					     lenp, ppos);
+}
+
 /**
  * struct do_proc_douintvec_minmax_conv_param - proc_douintvec_minmax() range checking structure
  * @min: pointer to minimum allowable value
@@ -1522,6 +1531,7 @@ PROC_HANDLER_ENOSYS(proc_do_large_bitmap);
 PROC_HANDLER_ENOSYS(proc_dobool_lockless);
 PROC_HANDLER_ENOSYS(proc_dointvec_lockless);
 PROC_HANDLER_ENOSYS(proc_douintvec_lockless);
+PROC_HANDLER_ENOSYS(proc_dointvec_minmax_lockless);
 
 #endif /* CONFIG_PROC_SYSCTL */
 
@@ -2435,3 +2445,4 @@ EXPORT_SYMBOL(proc_do_large_bitmap);
 EXPORT_SYMBOL(proc_dobool_lockless);
 EXPORT_SYMBOL(proc_dointvec_lockless);
 EXPORT_SYMBOL(proc_douintvec_lockless);
+EXPORT_SYMBOL(proc_dointvec_minmax_lockless);
-- 
2.30.2