Commit b492e95b authored by Jens Axboe's avatar Jens Axboe

pipe: set lower and upper limit on max pages in the pipe page array

We need at least two to guarantee proper POSIX behaviour, so
never allow a smaller limit than that.

Also expose a /proc/sys/fs/pipe-max-pages sysctl file that allows
root to define a sane upper limit. Make it default to 16 times the
default size, which is 16 pages.
Signed-off-by: default avatarJens Axboe <jens.axboe@oracle.com>
parent 35f3d14d
......@@ -19,10 +19,17 @@
#include <linux/pagemap.h>
#include <linux/audit.h>
#include <linux/syscalls.h>
#include <linux/fcntl.h>
#include <asm/uaccess.h>
#include <asm/ioctls.h>
/*
* The max size that a non-root user is allowed to grow the pipe. Can
* be set by root in /proc/sys/fs/pipe-max-pages
*/
unsigned int pipe_max_pages = PIPE_DEF_BUFFERS * 16;
/*
* We use a start+len construction, which provides full use of the
* allocated memory.
......@@ -1162,6 +1169,14 @@ long pipe_fcntl(struct file *file, unsigned int cmd, unsigned long arg)
switch (cmd) {
case F_SETPIPE_SZ:
if (!capable(CAP_SYS_ADMIN) && arg > pipe_max_pages)
return -EINVAL;
/*
* The pipe needs to be at least 2 pages large to
* guarantee POSIX behaviour.
*/
if (arg < 2)
return -EINVAL;
ret = pipe_set_size(pipe, arg);
break;
case F_GETPIPE_SZ:
......
......@@ -139,6 +139,8 @@ void pipe_lock(struct pipe_inode_info *);
void pipe_unlock(struct pipe_inode_info *);
void pipe_double_lock(struct pipe_inode_info *, struct pipe_inode_info *);
extern unsigned int pipe_max_pages;
/* Drop the inode semaphore and wait for a pipe event, atomically */
void pipe_wait(struct pipe_inode_info *pipe);
......
......@@ -52,6 +52,7 @@
#include <linux/slow-work.h>
#include <linux/perf_event.h>
#include <linux/kprobes.h>
#include <linux/pipe_fs_i.h>
#include <asm/uaccess.h>
#include <asm/processor.h>
......@@ -1423,6 +1424,14 @@ static struct ctl_table fs_table[] = {
.child = binfmt_misc_table,
},
#endif
{
.procname = "pipe-max-pages",
.data = &pipe_max_pages,
.maxlen = sizeof(int),
.mode = 0644,
.proc_handler = &proc_dointvec_minmax,
.extra1 = &two,
},
/*
* NOTE: do not add new entries to this table unless you have read
* Documentation/sysctl/ctl_unnumbered.txt
......
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