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Subject[PATCH 1/8] vfs: fix too big f_pos handling
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.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.

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: Heiko Carstens <heiko.carstens@de.ibm.com>
Reviewed-by: Wu Fengguang <fengguang.wu@intel.com>
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
---
drivers/char/mem.c | 4 ++++
fs/proc/base.c | 2 ++
fs/read_write.c | 22 ++++++++++++++++++++--
include/linux/fs.h | 2 ++
4 files changed, 28 insertions(+), 2 deletions(-)
--- linux-mm.orig/fs/read_write.c 2010-01-13 21:23:04.000000000 +0800
+++ linux-mm/fs/read_write.c 2010-01-13 21:23:52.000000000 +0800
@@ -205,6 +205,21 @@ bad:
}
#endif

+static int
+__negative_fpos_check(struct inode *inode, 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 !VERYBIG inode, negative pos(pos+count) is not allowed */
+ if (!IS_VERYBIG(inode))
+ return -EINVAL;
+ return 0;
+}
+
/*
* rw_verify_area doesn't like huge counts. We limit
* them to something that fits in "int" so that others
@@ -222,8 +237,11 @@ 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(inode, pos, count);
+ if (retval)
+ return retval;
+ }

if (unlikely(inode->i_flock && mandatory_lock(inode))) {
retval = locks_mandatory_area(
--- linux-mm.orig/include/linux/fs.h 2010-01-13 21:23:04.000000000 +0800
+++ linux-mm/include/linux/fs.h 2010-01-13 21:31:02.000000000 +0800
@@ -235,6 +235,7 @@ struct inodes_stat_t {
#define S_NOCMTIME 128 /* Do not update file c/mtime */
#define S_SWAPFILE 256 /* Do not truncate: swapon got its bmaps */
#define S_PRIVATE 512 /* Inode is fs-internal */
+#define S_VERYBIG 1024 /* Inode is huge: treat loff_t as unsigned */

/*
* Note that nosuid etc flags are inode-specific: setting some file-system
@@ -269,6 +270,7 @@ struct inodes_stat_t {
#define IS_NOCMTIME(inode) ((inode)->i_flags & S_NOCMTIME)
#define IS_SWAPFILE(inode) ((inode)->i_flags & S_SWAPFILE)
#define IS_PRIVATE(inode) ((inode)->i_flags & S_PRIVATE)
+#define IS_VERYBIG(inode) ((inode)->i_flags & S_VERYBIG)

/* the read-only stuff doesn't really belong here, but any other place is
probably as bad and I don't want to create yet another include file. */
--- linux-mm.orig/drivers/char/mem.c 2010-01-13 21:23:11.000000000 +0800
+++ linux-mm/drivers/char/mem.c 2010-01-13 21:27:28.000000000 +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)
+ inode->i_flags |= S_VERYBIG;
+
if (dev->fops->open)
return dev->fops->open(inode, filp);

--- linux-mm.orig/fs/proc/base.c 2010-01-13 21:23:04.000000000 +0800
+++ linux-mm/fs/proc/base.c 2010-01-13 21:27:51.000000000 +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);
+ /* this file is read only and we can catch out-of-range */
+ inode->i_flags |= S_VERYBIG;
return 0;
}




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