Commit 98159d97 authored by Joe Lawrence's avatar Joe Lawrence Committed by Linus Torvalds

pipe: match pipe_max_size data type with procfs

Patch series "A few round_pipe_size() and pipe-max-size fixups", v3.

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.

  4 - unsigned long -> unsigned int conversion makes for potential odd
      return errors from do_proc_douintvec_minmax_conv() and

This version underwent the same testing as v1:

This patch (of 4):

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

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

Link: Joe Lawrence's avatarJoe Lawrence <>
Reported-by: default avatarMikulas Patocka <>
Reviewed-by: default avatarMikulas Patocka <>
Cc: Michael Kerrisk <>
Cc: Randy Dunlap <>
Cc: Al Viro <>
Cc: Jens Axboe <>
Cc: Josh Poimboeuf <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent ecc0c469
......@@ -1125,7 +1125,7 @@ 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;
......@@ -1816,7 +1816,7 @@ static struct ctl_table fs_table[] = {
.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,
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