[PATCH 0/3] A few round_pipe_size() and pipe-max-size fixups

[PATCH 0/3] A few round_pipe_size() and pipe-max-size fixups

[Joe Lawrence]

While backporting Michael's "pipe: fix limit handling" patchset to a
distro-kernel, Mikulas noticed that current upstream pipe limit handling
contains a few problems:

  1 - procfs signed wrap: echo'ing a large number into
      /proc/sys/fs/pipe-max-size and then cat'ing it back out shows a
      negative value.

  2 - round_pipe_size() nr_pages overflow on 32bit:  this would
      subsequently try roundup_pow_of_two(0), which is undefined.

  3 - visible non-rounded pipe-max-size value: there is no mutual
      exclusion or protection between the time pipe_max_size is assigned
      a raw value from proc_dointvec_minmax() and when it is rounded.

v1 (differences from initial rfc):

- Re-arrange patchset order, push smaller fixes to the front

- Add a check so that round_pipe_size(size < pipe_min_size) will round
  up to round_pipe_size(pipe_min_size) as per man page [RD]

- Add new procfs proc_dopipe_max_size() and helpers to consolidate user
  space read / type validation / rounding / assignment [MP]


Testing
=======

Tests run on both 32 and 64-bit kernels.


Patch 1 - procfs signed wrap
----------------------------
Before:

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

After:

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


Patch 2 - 32bit overflow
------------------------
>From userspace:

  fcntl(fd, F_SETPIPE_SZ, 0xffffffff);

- Before: return value was 4096 (due to overflow) and was set to 4096
- After: returns -1 and sets errno EINVAL, pipe size remains untouched


Patch 3 - non-rounded pipe-max-size value
-----------------------------------------
Keep plugging in values that need to be rounded:

  while (true); do echo 1048570 > /proc/sys/fs/pipe-max-size; done

and in another terminal, loop around reading the value:

  time (while (true); do SIZE=$(cat /proc/sys/fs/pipe-max-size); [[ $(( $SIZE % 4096 )) -ne 0 ]] && break; done; echo "$SIZE")
  1048570

  real    0m46.213s
  user    0m29.688s
  sys     0m20.042s

- Before: found a non-rounded value within a few minutes
- After:  never encountered a non-page-rounded value


Joe Lawrence (3):
  pipe: match pipe_max_size data type with procfs
  pipe: avoid round_pipe_size() nr_pages overflow on 32-bit
  pipe: add proc_dopipe_max_size() to safely assign pipe_max_size

 fs/pipe.c                 | 21 +++++++++++----------
 include/linux/pipe_fs_i.h |  1 +
 include/linux/sysctl.h    |  3 +++
 kernel/sysctl.c           | 45 ++++++++++++++++++++++++++++++++++++++++++++-
 4 files changed, 59 insertions(+), 11 deletions(-)

-- 
1.8.3.1

[PATCH 1/3] pipe: match pipe_max_size data type with procfs

[Joe Lawrence]

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@redhat.com>
Signed-off-by: Joe Lawrence <joe.lawrence@redhat.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 97e5be897753..a21ad26de557 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -1124,7 +1124,7 @@ int pipe_proc_fn(struct ctl_table *table, int write, void __user *buf,
 {
 	int ret;
 
-	ret = proc_dointvec_minmax(table, write, buf, lenp, ppos);
+	ret = proc_douintvec_minmax(table, write, buf, lenp, ppos);
 	if (ret < 0 || !write)
 		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

[PATCH 2/3] pipe: avoid round_pipe_size() nr_pages overflow on 32-bit

[Joe Lawrence]

The round_pipe_size() function contains a right-bit-shift expression
which may overflow, which would cause undefined results in a subsequent
roundup_pow_of_two() call.

  static inline unsigned int round_pipe_size(unsigned int size)
  {
          unsigned long nr_pages;

          nr_pages = (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
          return roundup_pow_of_two(nr_pages) << PAGE_SHIFT;
  }

PAGE_SIZE is defined as (1UL << PAGE_SHIFT), so:
  - 4 bytes wide on 32-bit (0 to 0xffffffff)
  - 8 bytes wide on 64-bit (0 to 0xffffffffffffffff)

That means that 32-bit round_pipe_size(), nr_pages may overflow to 0:

  size=0x00000000    nr_pages=0x0
  size=0x00000001    nr_pages=0x1
  size=0xfffff000    nr_pages=0xfffff
  size=0xfffff001    nr_pages=0x0         << !
  size=0xffffffff    nr_pages=0x0         << !

This is bad because roundup_pow_of_two(n) is undefined when n == 0!

64-bit is not a problem as the unsigned int size is 4 bytes wide
(similar to 32-bit) and the larger, 8 byte wide unsigned long, is
sufficient to handle the largest value of the bit shift expression:

  size=0xffffffff    nr_pages=100000

Modify round_pipe_size() to return 0 if n == 0 and updates its callers
to handle accordingly.

Reported-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Joe Lawrence <joe.lawrence@redhat.com>
---
 fs/pipe.c | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/fs/pipe.c b/fs/pipe.c
index a21ad26de557..8cbc97d97753 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -1017,13 +1017,19 @@ static int fifo_open(struct inode *inode, struct file *filp)
 
 /*
  * Currently we rely on the pipe array holding a power-of-2 number
- * of pages.
+ * of pages. Returns 0 on error.
  */
 static inline unsigned int round_pipe_size(unsigned int size)
 {
 	unsigned long nr_pages;
 
+	if (size < pipe_min_size)
+		size = pipe_min_size;
+
 	nr_pages = (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
+	if (nr_pages == 0)
+		return 0;
+
 	return roundup_pow_of_two(nr_pages) << PAGE_SHIFT;
 }
 
@@ -1039,6 +1045,8 @@ static long pipe_set_size(struct pipe_inode_info *pipe, unsigned long arg)
 	long ret = 0;
 
 	size = round_pipe_size(arg);
+	if (size == 0)
+		return -EINVAL;
 	nr_pages = size >> PAGE_SHIFT;
 
 	if (!nr_pages)
@@ -1122,13 +1130,18 @@ static long pipe_set_size(struct pipe_inode_info *pipe, unsigned long arg)
 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_douintvec_minmax(table, write, buf, lenp, ppos);
 	if (ret < 0 || !write)
 		return ret;
 
-	pipe_max_size = round_pipe_size(pipe_max_size);
+	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;
 }
 
-- 
1.8.3.1

[PATCH 3/3] pipe: add proc_dopipe_max_size() to safely assign pipe_max_size

[Joe Lawrence]

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 racey:

  pipe.c :: alloc_pipe_info()
  pipe.c :: pipe_set_size()

Add a new proc_dopipe_max_size() function 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.

Reported-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Joe Lawrence <joe.lawrence@redhat.com>
---
 fs/pipe.c                 | 16 ++--------------
 include/linux/pipe_fs_i.h |  1 +
 include/linux/sysctl.h    |  3 +++
 kernel/sysctl.c           | 43 +++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 49 insertions(+), 14 deletions(-)

diff --git a/fs/pipe.c b/fs/pipe.c
index 8cbc97d97753..4db3cd2d139c 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -1019,7 +1019,7 @@ static int fifo_open(struct inode *inode, struct file *filp)
  * 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;
 
@@ -1130,19 +1130,7 @@ static long pipe_set_size(struct pipe_inode_info *pipe, unsigned long arg)
 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_douintvec_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);
 }
 
 /*
diff --git a/include/linux/pipe_fs_i.h b/include/linux/pipe_fs_i.h
index e7497c9dde7f..485cf7a7aa8f 100644
--- a/include/linux/pipe_fs_i.h
+++ b/include/linux/pipe_fs_i.h
@@ -190,5 +190,6 @@ static inline int pipe_buf_steal(struct pipe_inode_info *pipe,
 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
diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
index 1d4dba490fb6..ba24ca72800c 100644
--- a/include/linux/sysctl.h
+++ b/include/linux/sysctl.h
@@ -50,6 +50,9 @@ extern int proc_dointvec_minmax(struct ctl_table *, int,
 extern int proc_douintvec_minmax(struct ctl_table *table, int write,
 				 void __user *buffer, size_t *lenp,
 				 loff_t *ppos);
+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,
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index c976719bf37a..7a2913c5546e 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -67,6 +67,7 @@
 #include <linux/kexec.h>
 #include <linux/bpf.h>
 #include <linux/mount.h>
+#include <linux/pipe_fs_i.h>
 
 #include <linux/uaccess.h>
 #include <asm/processor.h>
@@ -2631,6 +2632,47 @@ int proc_douintvec_minmax(struct ctl_table *table, int write,
 				 do_proc_douintvec_minmax_conv, &param);
 }
 
+struct do_proc_dopipe_max_size_conv_param {
+	unsigned int *min;
+};
+
+static int do_proc_dopipe_max_size_conv(unsigned long *lvalp,
+					unsigned 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 (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;
+		*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_douintvec(table, write, buffer, lenp, ppos,
+				 do_proc_dopipe_max_size_conv, &param);
+}
+
 static void validate_coredump_safety(void)
 {
 #ifdef CONFIG_COREDUMP
@@ -3179,6 +3221,7 @@ int proc_doulongvec_ms_jiffies_minmax(struct ctl_table *table, int write,
 EXPORT_SYMBOL(proc_dointvec_jiffies);
 EXPORT_SYMBOL(proc_dointvec_minmax);
 EXPORT_SYMBOL_GPL(proc_douintvec_minmax);
+EXPORT_SYMBOL_GPL(proc_dopipe_max_size);
 EXPORT_SYMBOL(proc_dointvec_userhz_jiffies);
 EXPORT_SYMBOL(proc_dointvec_ms_jiffies);
 EXPORT_SYMBOL(proc_dostring);
-- 
1.8.3.1

Re: [PATCH 3/3] pipe: add proc_dopipe_max_size() to safely assign pipe_max_size

[kbuild test robot]

[-- Attachment #1: Type: text/plain, Size: 824 bytes --]

Hi Joe,

[auto build test ERROR on linus/master]
[also build test ERROR on v4.14-rc2 next-20170928]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url:    https://github.com/0day-ci/linux/commits/Joe-Lawrence/A-few-round_pipe_size-and-pipe-max-size-fixups/20170929-205234
config: i386-tinyconfig (attached as .config)
compiler: gcc-6 (Debian 6.2.0-3) 6.2.0 20160901
reproduce:
        # save the attached .config to linux build tree
        make ARCH=i386 

All errors (new ones prefixed by >>):

   fs/pipe.o: In function `pipe_proc_fn':
>> pipe.c:(.text+0xe90): undefined reference to `proc_dopipe_max_size'

---
0-DAY kernel test infrastructure                Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all                   Intel Corporation

[-- Attachment #2: .config.gz --]
[-- Type: application/gzip, Size: 6685 bytes --]

Re: [PATCH 3/3] pipe: add proc_dopipe_max_size() to safely assign pipe_max_size

[kbuild test robot]

[-- Attachment #1: Type: text/plain, Size: 1344 bytes --]

Hi Joe,

[auto build test ERROR on linus/master]
[also build test ERROR on v4.14-rc2 next-20170929]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url:    https://github.com/0day-ci/linux/commits/Joe-Lawrence/A-few-round_pipe_size-and-pipe-max-size-fixups/20170929-205234
config: h8300-h8300h-sim_defconfig (attached as .config)
compiler: h8300-linux-gcc (GCC) 6.2.0
reproduce:
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # save the attached .config to linux build tree
        make.cross ARCH=h8300 

All errors (new ones prefixed by >>):

   fs/pipe.o: In function `pipe_proc_fn':
>> fs/pipe.c:1133: undefined reference to `proc_dopipe_max_size'

vim +1133 fs/pipe.c

  1125	
  1126	/*
  1127	 * This should work even if CONFIG_PROC_FS isn't set, as proc_dointvec_minmax
  1128	 * will return an error.
  1129	 */
  1130	int pipe_proc_fn(struct ctl_table *table, int write, void __user *buf,
  1131			 size_t *lenp, loff_t *ppos)
  1132	{
> 1133		return proc_dopipe_max_size(table, write, buf, lenp, ppos);
  1134	}
  1135	

---
0-DAY kernel test infrastructure                Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all                   Intel Corporation

[-- Attachment #2: .config.gz --]
[-- Type: application/gzip, Size: 4713 bytes --]

[PATCH v2 3/3] pipe: add proc_dopipe_max_size() to safely assign pipe_max_size

[Joe Lawrence]

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 racey:

  pipe.c :: alloc_pipe_info()
  pipe.c :: pipe_set_size()

Add a new proc_dopipe_max_size() function 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.

Reported-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Joe Lawrence <joe.lawrence@redhat.com>
---

v2:

 - Fix !CONFIG_PROC_SYSCTL build case

 fs/pipe.c                 | 16 ++--------------
 include/linux/pipe_fs_i.h |  1 +
 include/linux/sysctl.h    |  3 +++
 kernel/sysctl.c           | 49 +++++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 55 insertions(+), 14 deletions(-)

diff --git a/fs/pipe.c b/fs/pipe.c
index 8cbc97d97753..4db3cd2d139c 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -1019,7 +1019,7 @@ static int fifo_open(struct inode *inode, struct file *filp)
  * 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;
 
@@ -1130,19 +1130,7 @@ static long pipe_set_size(struct pipe_inode_info *pipe, unsigned long arg)
 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_douintvec_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);
 }
 
 /*
diff --git a/include/linux/pipe_fs_i.h b/include/linux/pipe_fs_i.h
index e7497c9dde7f..485cf7a7aa8f 100644
--- a/include/linux/pipe_fs_i.h
+++ b/include/linux/pipe_fs_i.h
@@ -190,5 +190,6 @@ static inline int pipe_buf_steal(struct pipe_inode_info *pipe,
 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
diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
index 1d4dba490fb6..ba24ca72800c 100644
--- a/include/linux/sysctl.h
+++ b/include/linux/sysctl.h
@@ -50,6 +50,9 @@ extern int proc_dointvec_minmax(struct ctl_table *, int,
 extern int proc_douintvec_minmax(struct ctl_table *table, int write,
 				 void __user *buffer, size_t *lenp,
 				 loff_t *ppos);
+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,
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index c976719bf37a..30b01b22014d 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -67,6 +67,7 @@
 #include <linux/kexec.h>
 #include <linux/bpf.h>
 #include <linux/mount.h>
+#include <linux/pipe_fs_i.h>
 
 #include <linux/uaccess.h>
 #include <asm/processor.h>
@@ -2631,6 +2632,47 @@ int proc_douintvec_minmax(struct ctl_table *table, int write,
 				 do_proc_douintvec_minmax_conv, &param);
 }
 
+struct do_proc_dopipe_max_size_conv_param {
+	unsigned int *min;
+};
+
+static int do_proc_dopipe_max_size_conv(unsigned long *lvalp,
+					unsigned 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 (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;
+		*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_douintvec(table, write, buffer, lenp, ppos,
+				 do_proc_dopipe_max_size_conv, &param);
+}
+
 static void validate_coredump_safety(void)
 {
 #ifdef CONFIG_COREDUMP
@@ -3136,6 +3178,12 @@ int proc_douintvec_minmax(struct ctl_table *table, int write,
 	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)
 {
@@ -3179,6 +3227,7 @@ int proc_doulongvec_ms_jiffies_minmax(struct ctl_table *table, int write,
 EXPORT_SYMBOL(proc_dointvec_jiffies);
 EXPORT_SYMBOL(proc_dointvec_minmax);
 EXPORT_SYMBOL_GPL(proc_douintvec_minmax);
+EXPORT_SYMBOL_GPL(proc_dopipe_max_size);
 EXPORT_SYMBOL(proc_dointvec_userhz_jiffies);
 EXPORT_SYMBOL(proc_dointvec_ms_jiffies);
 EXPORT_SYMBOL(proc_dostring);
-- 
1.8.3.1