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

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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: Jens Axboe <jens.axboe@oracle.com>
This commit is contained in:
Jens Axboe 2010-05-19 21:03:16 +02:00
parent 35f3d14dbb
commit b492e95be0
3 changed files with 26 additions and 0 deletions
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15
fs/pipe.c
View File

@ -19,10 +19,17 @@
#include <linux/pagemap.h> #include <linux/pagemap.h>
#include <linux/audit.h> #include <linux/audit.h>
#include <linux/syscalls.h> #include <linux/syscalls.h>
#include <linux/fcntl.h>
#include <asm/uaccess.h> #include <asm/uaccess.h>
#include <asm/ioctls.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 * We use a start+len construction, which provides full use of the
* allocated memory. * allocated memory.
@ -1162,6 +1169,14 @@ long pipe_fcntl(struct file *file, unsigned int cmd, unsigned long arg)
switch (cmd) { switch (cmd) {
case F_SETPIPE_SZ: 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); ret = pipe_set_size(pipe, arg);
break; break;
case F_GETPIPE_SZ: case F_GETPIPE_SZ:

2
include/linux/pipe_fs_i.h
View File

@ -139,6 +139,8 @@ void pipe_lock(struct pipe_inode_info *);
void pipe_unlock(struct pipe_inode_info *); void pipe_unlock(struct pipe_inode_info *);
void pipe_double_lock(struct pipe_inode_info *, 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 */ /* Drop the inode semaphore and wait for a pipe event, atomically */
void pipe_wait(struct pipe_inode_info *pipe); void pipe_wait(struct pipe_inode_info *pipe);

9
kernel/sysctl.c
View File

@ -52,6 +52,7 @@
#include <linux/slow-work.h> #include <linux/slow-work.h>
#include <linux/perf_event.h> #include <linux/perf_event.h>
#include <linux/kprobes.h> #include <linux/kprobes.h>
#include <linux/pipe_fs_i.h>
#include <asm/uaccess.h> #include <asm/uaccess.h>
#include <asm/processor.h> #include <asm/processor.h>
@ -1423,6 +1424,14 @@ static struct ctl_table fs_table[] = {
.child = binfmt_misc_table, .child = binfmt_misc_table,
}, },
#endif #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 * NOTE: do not add new entries to this table unless you have read
* Documentation/sysctl/ctl_unnumbered.txt * Documentation/sysctl/ctl_unnumbered.txt