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Commit 7a8d1819 authored by Joe Lawrence's avatar Joe Lawrence Committed by Linus Torvalds
Browse files

pipe: add proc_dopipe_max_size() to safely assign pipe_max_size 

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: default avatarJoe Lawrence <joe.lawrence@redhat.com>
Reported-by: default avatarMikulas Patocka <mpatocka@redhat.com>
Reviewed-by: default avatarMikulas Patocka <mpatocka@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Michael Kerrisk <mtk.manpages@gmail.com>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent d3f14c48

fs/pipe.c

+3 −15
Original line number Diff line number Diff line
@@ -1020,7 +1020,7 @@ const struct file_operations pipefifo_fops = { 
 * 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;
@@ -1125,25 +1125,13 @@ static long pipe_set_size(struct pipe_inode_info *pipe, unsigned long arg) 
}



/*

 * 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_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);

}



/*

include/linux/pipe_fs_i.h

+1 −0
Original line number Diff line number Diff line
@@ -191,5 +191,6 @@ long pipe_fcntl(struct file *, unsigned int, unsigned long arg); 
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

include/linux/sysctl.h

+3 −0
Original line number Diff line number Diff line
@@ -51,6 +51,9 @@ 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,

kernel/sysctl.c

+49 −0
Original line number Diff line number Diff line
@@ -66,6 +66,7 @@ 
#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>
@@ -2620,6 +2621,47 @@ 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
@@ -3125,6 +3167,12 @@ 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)

{
@@ -3168,6 +3216,7 @@ EXPORT_SYMBOL(proc_douintvec); 
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);