From: Joe Lawrence <joe.lawrence@xxxxxxxxxx>
Subject: 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
do_proc_dopipe_max_size_conv().
This version underwent the same testing as v1:
https://marc.info/?l=linux-kernel&m=150643571406022&w=2
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
-2147483648
Use unsigned operations on this variable to avoid such negative values.
Link: http://lkml.kernel.org/r/1507658689-11669-2-git-send-email-joe.lawrence@xxxxxxxxxx
Signed-off-by: Joe Lawrence <joe.lawrence@xxxxxxxxxx>
Reported-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
Reviewed-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
Cc: Michael Kerrisk <mtk.manpages@xxxxxxxxx>
Cc: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Jens Axboe <axboe@xxxxxxxxx>
Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/pipe.c | 2 +-
kernel/sysctl.c | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)
diff -puN fs/pipe.c~pipe-match-pipe_max_size-data-type-with-procfs fs/pipe.c
--- a/fs/pipe.c~pipe-match-pipe_max_size-data-type-with-procfs
+++ a/fs/pipe.c
@@ -1125,7 +1125,7 @@ int pipe_proc_fn(struct ctl_table *table
{
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 -puN kernel/sysctl.c~pipe-match-pipe_max_size-data-type-with-procfs kernel/sysctl.c
--- a/kernel/sysctl.c~pipe-match-pipe_max_size-data-type-with-procfs
+++ a/kernel/sysctl.c
@@ -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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