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Commit b492e95b authored by Jens Axboe's avatar Jens Axboe
Browse files

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

fs/pipe.c

+15 −0
Original line number Diff line number Diff line
@@ -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:

include/linux/pipe_fs_i.h

+2 −0
Original line number Diff line number Diff line
@@ -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);

kernel/sysctl.c

+9 −0
Original line number Diff line number Diff line
@@ -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