linux-kernel - [PATCH RFC 3/3] pipe: match pipe_max

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Message-Id: <1504622676-2992-4-git-send-email-joe.lawrence@redhat.com>
Date:   Tue,  5 Sep 2017 10:44:36 -0400
From:   Joe Lawrence <joe.lawrence@...hat.com>
To:     linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        "Luis R. Rodriguez" <mcgrof@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Mikulas Patocka <mpatocka@...hat.com>,
        Michael Kerrisk <mtk.manpages@...il.com>
Subject: [PATCH RFC 3/3] pipe: match pipe_max_size data type with procfs

pipe_max_size is defined as an unsigned int:

  unsigned int pipe_max_size = 1048576;

but its procfs/sysctl representation is an integer:

  static struct ctl_table fs_table[] = {
          ...
          {
                  .procname       = "pipe-max-size",
                  .data           = &pipe_max_size,
                  .maxlen         = sizeof(int),
                  .mode           = 0644,
                  .proc_handler   = &pipe_proc_fn,
                  .extra1         = &pipe_min_size,
          },
          ...

that is signed:

  int pipe_proc_fn(struct ctl_table *table, int write, void __user *buf,
                   size_t *lenp, loff_t *ppos)
  {
          ...
          ret = proc_dointvec_minmax(table, write, buf, lenp, ppos)

This leads to signed results via procfs for large values of
pipe_max_size:

  % echo 2147483647 >/proc/sys/fs/pipe-max-size
  % cat /proc/sys/fs/pipe-max-size
  -2147483648

Use unsigned operations on this variable to avoid such negative values.

Reported-by: Mikulas Patocka <mpatocka@...hat.com>
Signed-off-by: Joe Lawrence <joe.lawrence@...hat.com>
---
 fs/pipe.c       | 2 +-
 kernel/sysctl.c | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/pipe.c b/fs/pipe.c
index 33bb11b0d78e..3b10d39cc5d1 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -1147,7 +1147,7 @@ int pipe_proc_fn(struct ctl_table *table, int write, void __user *buf,
 
 	mutex_lock(&pipe_max_mutex);
 	orig_pipe_max_size = pipe_max_size;
-	ret = proc_dointvec_minmax(table, write, buf, lenp, ppos);
+	ret = proc_douintvec_minmax(table, write, buf, lenp, ppos);
 	if (ret < 0 || !write) {
 		mutex_unlock(&pipe_max_mutex);
 		return ret;
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 6648fbbb8157..c976719bf37a 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -1825,7 +1825,7 @@ static int sysrq_sysctl_handler(struct ctl_table *table, int write,
 	{
 		.procname	= "pipe-max-size",
 		.data		= &pipe_max_size,
-		.maxlen		= sizeof(int),
+		.maxlen		= sizeof(pipe_max_size),
 		.mode		= 0644,
 		.proc_handler	= &pipe_proc_fn,
 		.extra1		= &pipe_min_size,
-- 
1.8.3.1