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

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.comSigned-off-by: 's avatarJoe Lawrence <joe.lawrence@redhat.com>
Reported-by: 's avatarMikulas Patocka <mpatocka@redhat.com>
Reviewed-by: 's 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: 's avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: 's avatarLinus Torvalds <torvalds@linux-foundation.org>
parent d3f14c48
......@@ -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);
}
/*
......
......@@ -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
......@@ -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,
......
......@@ -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);
......
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