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Message-ID: <lsq.1528380321.972258691@decadent.org.uk>
Date: Thu, 07 Jun 2018 15:05:21 +0100
From: Ben Hutchings <ben@...adent.org.uk>
To: linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC: akpm@...ux-foundation.org,
"Linus Torvalds" <torvalds@...ux-foundation.org>,
"Josh Poimboeuf" <jpoimboe@...hat.com>,
"Michael Kerrisk" <mtk.manpages@...il.com>,
"Randy Dunlap" <rdunlap@...radead.org>,
"Al Viro" <viro@...iv.linux.org.uk>,
"Joe Lawrence" <joe.lawrence@...hat.com>,
"Mikulas Patocka" <mpatocka@...hat.com>,
"Jens Axboe" <axboe@...nel.dk>
Subject: [PATCH 3.16 208/410] pipe: add proc_dopipe_max_size() to safely
assign pipe_max_size
3.16.57-rc1 review patch. If anyone has any objections, please let me know.
------------------
From: Joe Lawrence <joe.lawrence@...hat.com>
commit 7a8d181949fb2c16be00f8cdb354794a30e46b39 upstream.
pipe_max_size is assigned directly via procfs sysctl:
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,
},
...
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)
...
and then later rounded in-place a few statements later:
...
pipe_max_size = round_pipe_size(pipe_max_size);
...
This leaves a window of time between initial assignment and rounding
that may be visible to other threads. (For example, one thread sets a
non-rounded value to pipe_max_size while another reads its value.)
Similar reads of pipe_max_size are potentially racy:
pipe.c :: alloc_pipe_info()
pipe.c :: pipe_set_size()
Add a new proc_dopipe_max_size() that consolidates reading the new value
from the user buffer, verifying bounds, and calling round_pipe_size()
with a single assignment to pipe_max_size.
Link: http://lkml.kernel.org/r/1507658689-11669-4-git-send-email-joe.lawrence@redhat.com
Signed-off-by: Joe Lawrence <joe.lawrence@...hat.com>
Reported-by: Mikulas Patocka <mpatocka@...hat.com>
Reviewed-by: Mikulas Patocka <mpatocka@...hat.com>
Cc: Al Viro <viro@...iv.linux.org.uk>
Cc: Jens Axboe <axboe@...nel.dk>
Cc: Michael Kerrisk <mtk.manpages@...il.com>
Cc: Randy Dunlap <rdunlap@...radead.org>
Cc: Josh Poimboeuf <jpoimboe@...hat.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
[bwh: Backported to 3.16: Continue using int sysctl functions because we don't
have proper unsigned int support]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -1008,7 +1008,7 @@ const struct file_operations pipefifo_fo
* Currently we rely on the pipe array holding a power-of-2 number
* of pages. Returns 0 on error.
*/
-static inline unsigned int round_pipe_size(unsigned int size)
+unsigned int round_pipe_size(unsigned int size)
{
unsigned long nr_pages;
@@ -1112,25 +1112,13 @@ out_revert_acct:
}
/*
- * This should work even if CONFIG_PROC_FS isn't set, as proc_dointvec_minmax
+ * This should work even if CONFIG_PROC_FS isn't set, as proc_dopipe_max_size
* will return an error.
*/
int pipe_proc_fn(struct ctl_table *table, int write, void __user *buf,
size_t *lenp, loff_t *ppos)
{
- unsigned int rounded_pipe_max_size;
- int ret;
-
- ret = proc_dointvec_minmax(table, write, buf, lenp, ppos);
- if (ret < 0 || !write)
- return ret;
-
- rounded_pipe_max_size = round_pipe_size(pipe_max_size);
- if (rounded_pipe_max_size == 0)
- return -EINVAL;
-
- pipe_max_size = rounded_pipe_max_size;
- return ret;
+ return proc_dopipe_max_size(table, write, buf, lenp, ppos);
}
/*
--- a/include/linux/pipe_fs_i.h
+++ b/include/linux/pipe_fs_i.h
@@ -149,5 +149,6 @@ long pipe_fcntl(struct file *, unsigned
struct pipe_inode_info *get_pipe_info(struct file *file);
int create_pipe_files(struct file **, int);
+unsigned int round_pipe_size(unsigned int size);
#endif
--- a/include/linux/sysctl.h
+++ b/include/linux/sysctl.h
@@ -45,6 +45,9 @@ extern int proc_dointvec(struct ctl_tabl
void __user *, size_t *, loff_t *);
extern int proc_dointvec_minmax(struct ctl_table *, int,
void __user *, size_t *, loff_t *);
+extern int proc_dopipe_max_size(struct ctl_table *table, int write,
+ void __user *buffer, size_t *lenp,
+ loff_t *ppos);
extern int proc_dointvec_jiffies(struct ctl_table *, int,
void __user *, size_t *, loff_t *);
extern int proc_dointvec_userhz_jiffies(struct ctl_table *, int,
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -64,6 +64,7 @@
#include <linux/sched/sysctl.h>
#include <linux/kexec.h>
#include <linux/mount.h>
+#include <linux/pipe_fs_i.h>
#include <asm/uaccess.h>
#include <asm/processor.h>
@@ -2222,6 +2223,47 @@ int proc_dointvec_minmax(struct ctl_tabl
do_proc_dointvec_minmax_conv, ¶m);
}
+struct do_proc_dopipe_max_size_conv_param {
+ unsigned int *min;
+};
+
+static int do_proc_dopipe_max_size_conv(bool *negp, unsigned long *lvalp,
+ int *valp, int write, void *data)
+{
+ struct do_proc_dopipe_max_size_conv_param *param = data;
+
+ if (write) {
+ unsigned int val = round_pipe_size(*lvalp);
+
+ if (*negp || val == 0)
+ return -EINVAL;
+
+ if (param->min && *param->min > val)
+ return -ERANGE;
+
+ if (*lvalp > UINT_MAX)
+ return -EINVAL;
+
+ *valp = val;
+ } else {
+ unsigned int val = *valp;
+ *negp = false;
+ *lvalp = (unsigned long) val;
+ }
+
+ return 0;
+}
+
+int proc_dopipe_max_size(struct ctl_table *table, int write,
+ void __user *buffer, size_t *lenp, loff_t *ppos)
+{
+ struct do_proc_dopipe_max_size_conv_param param = {
+ .min = (unsigned int *) table->extra1,
+ };
+ return do_proc_dointvec(table, write, buffer, lenp, ppos,
+ do_proc_dopipe_max_size_conv, ¶m);
+}
+
static void validate_coredump_safety(void)
{
#ifdef CONFIG_COREDUMP
@@ -2737,6 +2779,12 @@ int proc_dointvec_minmax(struct ctl_tabl
return -ENOSYS;
}
+int proc_dopipe_max_size(struct ctl_table *table, int write,
+ void __user *buffer, size_t *lenp, loff_t *ppos)
+{
+ return -ENOSYS;
+}
+
int proc_dointvec_jiffies(struct ctl_table *table, int write,
void __user *buffer, size_t *lenp, loff_t *ppos)
{
@@ -2778,6 +2826,7 @@ int proc_doulongvec_ms_jiffies_minmax(st
EXPORT_SYMBOL(proc_dointvec);
EXPORT_SYMBOL(proc_dointvec_jiffies);
EXPORT_SYMBOL(proc_dointvec_minmax);
+EXPORT_SYMBOL_GPL(proc_dopipe_max_size);
EXPORT_SYMBOL(proc_dointvec_userhz_jiffies);
EXPORT_SYMBOL(proc_dointvec_ms_jiffies);
EXPORT_SYMBOL(proc_dostring);
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