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Date: Thu, 14 Jan 2010 21:56:05 +0800
From: Wu Fengguang <fengguang.wu@...el.com>
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc: Al Viro <viro@...IV.linux.org.uk>,
Andrew Morton <akpm@...ux-foundation.org>,
LKML <linux-kernel@...r.kernel.org>,
Heiko Carstens <heiko.carstens@...ibm.com>,
Andi Kleen <andi@...stfloor.org>,
Nick Piggin <npiggin@...e.de>,
Hugh Dickins <hugh.dickins@...cali.co.uk>,
Linux Memory Management List <linux-mm@...ck.org>,
"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH 1/8] vfs: fix too big f_pos handling
On Thu, Jan 14, 2010 at 01:42:50PM +0800, KAMEZAWA Hiroyuki wrote:
> On Thu, 14 Jan 2010 05:13:08 +0000
> Al Viro <viro@...IV.linux.org.uk> wrote:
>
> > On Wed, Jan 13, 2010 at 10:09:56PM +0800, Wu, Fengguang wrote:
> > > From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> > >
> > > Now, rw_verify_area() checsk f_pos is negative or not. And if
> > > negative, returns -EINVAL.
> > >
> > > But, some special files as /dev/(k)mem and /proc/<pid>/mem etc..
> > > has negative offsets. And we can't do any access via read/write
> > > to the file(device).
> > >
> > > This patch introduce a flag S_VERYBIG and allow negative file
> > > offsets.
> >
> > Ehh... FMODE_NEG_OFFSET in file->f_mode, perhaps?
> >
> Any method is okay for me.
> I was just not sure where I could modify without problem.
> If modifing f_mode is allowed, I'll write new version.
>
> Thank you for advice.
>
> I'm sorry that I don't have enough time this week. So, I'll try next week.
> I think dropping this patch itself has no big influence to this patch set.
> (but debug will be harder ;)
I just added FMODE_RANDOM, so hands down to add another ;)
Here is the updated patch, I'd like to submit it in another series
together with the FMODE_RANDOM patch.
Tested OK on /dev/kmem.
Thanks,
Fengguang
---
Subject: vfs: allow negative f_pos with FMODE_NEG_OFFSET
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Now, rw_verify_area() checsk f_pos is negative or not. And if
negative, returns -EINVAL.
But, some special files as /dev/(k)mem and /proc/<pid>/mem etc..
has negative offsets. And we can't do any access via read/write
to the file(device).
So introduce FMODE_NEG_OFFSET to allow negative file offsets.
Changelog: v5->v6
- use FMODE_NEG_OFFSET (suggested by Al)
- rebased onto 2.6.33-rc1
Changelog: v4->v5
- clean up patches dor /dev/mem.
- rebased onto 2.6.32-rc1
Changelog: v3->v4
- make changes in mem.c aligned.
- change __negative_fpos_check() to return int.
- fixed bug in "pos" check.
- added comments.
Changelog: v2->v3
- fixed bug in rw_verify_area (it cannot be compiled)
CC: Al Viro <viro@...IV.linux.org.uk>
CC: Heiko Carstens <heiko.carstens@...ibm.com>
Signed-off-by: Wu Fengguang <fengguang.wu@...el.com>
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
---
drivers/char/mem.c | 4 ++++
fs/proc/base.c | 2 ++
fs/read_write.c | 21 +++++++++++++++++++--
include/linux/fs.h | 3 +++
4 files changed, 28 insertions(+), 2 deletions(-)
--- linux.orig/fs/read_write.c 2010-01-14 21:28:00.000000000 +0800
+++ linux/fs/read_write.c 2010-01-14 21:30:41.000000000 +0800
@@ -205,6 +205,20 @@ bad:
}
#endif
+static int
+__negative_fpos_check(struct file *file, loff_t pos, size_t count)
+{
+ /*
+ * pos or pos+count is negative here, check overflow.
+ * too big "count" will be caught in rw_verify_area().
+ */
+ if ((pos < 0) && (pos + count < pos))
+ return -EOVERFLOW;
+ if (file->f_mode & FMODE_NEG_OFFSET)
+ return 0;
+ return -EINVAL;
+}
+
/*
* rw_verify_area doesn't like huge counts. We limit
* them to something that fits in "int" so that others
@@ -222,8 +236,11 @@ int rw_verify_area(int read_write, struc
if (unlikely((ssize_t) count < 0))
return retval;
pos = *ppos;
- if (unlikely((pos < 0) || (loff_t) (pos + count) < 0))
- return retval;
+ if (unlikely((pos < 0) || (loff_t) (pos + count) < 0)) {
+ retval = __negative_fpos_check(file, pos, count);
+ if (retval)
+ return retval;
+ }
if (unlikely(inode->i_flock && mandatory_lock(inode))) {
retval = locks_mandatory_area(
--- linux.orig/include/linux/fs.h 2010-01-14 21:28:00.000000000 +0800
+++ linux/include/linux/fs.h 2010-01-14 21:32:24.000000000 +0800
@@ -93,6 +93,9 @@ struct inodes_stat_t {
/* Expect random access pattern */
#define FMODE_RANDOM ((__force fmode_t)0x1000)
+/* File is huge (eg. /dev/kmem): treat loff_t as unsigned */
+#define FMODE_NEG_OFFSET ((__force fmode_t)0x2000)
+
/*
* The below are the various read and write types that we support. Some of
* them include behavioral modifiers that send information down to the
--- linux.orig/drivers/char/mem.c 2010-01-14 21:28:00.000000000 +0800
+++ linux/drivers/char/mem.c 2010-01-14 21:33:20.000000000 +0800
@@ -861,6 +861,10 @@ static int memory_open(struct inode *ino
if (dev->dev_info)
filp->f_mapping->backing_dev_info = dev->dev_info;
+ /* Is /dev/mem or /dev/kmem ? */
+ if (dev->dev_info == &directly_mappable_cdev_bdi)
+ filp->f_mode |= FMODE_NEG_OFFSET;
+
if (dev->fops->open)
return dev->fops->open(inode, filp);
--- linux.orig/fs/proc/base.c 2010-01-14 21:28:00.000000000 +0800
+++ linux/fs/proc/base.c 2010-01-14 21:37:08.000000000 +0800
@@ -861,6 +861,8 @@ static const struct file_operations proc
static int mem_open(struct inode* inode, struct file* file)
{
file->private_data = (void*)((long)current->self_exec_id);
+ /* OK to pass negative loff_t, we can catch out-of-range */
+ file->f_mode |= FMODE_NEG_OFFSET;
return 0;
}
--
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