On 09/20/2012 12:46 AM, Konrad Rzeszutek Wilk wrote:
On Tue, Sep 18, 2012 at 01:49:52PM -0700, Linus Torvalds wrote:
On Tue, Sep 18, 2012 at 1:37 PM, Konrad Rzeszutek Wilk
<[email protected]> wrote:
30 words. ~360 + 29 spaces + NULL = 390?
Just allocate the max then. That's tiny.
And it's actually just 330: max ten characters for an unsigned 32-bit number.
Linus,
Could you take a look at these two patches to see if I missed anything?
Thank you.
From 0806b133b5b28081adf23d0d04a99636ed3b861b Mon Sep 17 00:00:00 2001
From: Konrad Rzeszutek Wilk<[email protected]>
Date: Wed, 19 Sep 2012 11:23:01 -0400
Subject: [PATCH 1/2] debugfs: Add lock for u32_array_read
Dave Jones spotted that the u32_array_read was doing something funny:
=============================================================================
BUG kmalloc-64 (Not tainted): Redzone overwritten
-----------------------------------------------------------------------------
INFO: 0xffff88001f4b4970-0xffff88001f4b4977. First byte 0xbb instead of 0xcc
INFO: Allocated in u32_array_read+0xd1/0x110 age=0 cpu=6 pid=32767
__slab_alloc+0x516/0x5a5
__kmalloc+0x213/0x2c0
u32_array_read+0xd1/0x110
.. snip..
INFO: Freed in u32_array_read+0x99/0x110 age=0 cpu=0 pid=32749
__slab_free+0x3f/0x3bf
kfree+0x2d5/0x310
u32_array_read+0x99/0x110
Linus tracked it down and found out that "debugfs is racy for that case
[read calls in parallel on the debugfs]. At least the file->private_data
accesses are, for the case of that "u32_array" case.
In fact it is racy in ... the whole "file->private_data" access ..
If you have multiple readers on the same file, the whole
if (file->private_data) {
kfree(file->private_data);
file->private_data = NULL;
}
file->private_data = format_array_alloc("%u", data->array,
data->elements);
thing is just a disaster waiting to happen." He suggested
putting a lock which this patch does.
The consequence of this is that it will trigger more spinlock usage,
as this particular debugfs is used to provide a histogram of spinlock
contention. But memory corruption is a worst offender then that.
Reported-by: Dave Jones<[email protected]>
Suggested-by: Linus Torvalds<[email protected]>
Tested-by: Raghavendra <[email protected]>
---
fs/debugfs/file.c | 7 ++++++-
1 files changed, 6 insertions(+), 1 deletions(-)
diff --git a/fs/debugfs/file.c b/fs/debugfs/file.c
index 2340f69..c6d9088 100644
--- a/fs/debugfs/file.c
+++ b/fs/debugfs/file.c
@@ -524,6 +524,7 @@ EXPORT_SYMBOL_GPL(debugfs_create_blob);
struct array_data {
void *array;
u32 elements;
+ struct mutex lock;
};
static int u32_array_open(struct inode *inode, struct file *file)
@@ -580,6 +581,7 @@ static ssize_t u32_array_read(struct file *file, char
__user *buf, size_t len,
struct array_data *data = inode->i_private;
size_t size;
+ mutex_lock(&data->lock);
if (*ppos == 0) {
if (file->private_data) {
kfree(file->private_data);
@@ -594,8 +596,10 @@ static ssize_t u32_array_read(struct file *file, char
__user *buf, size_t len,
if (file->private_data)
size = strlen(file->private_data);
- return simple_read_from_buffer(buf, len, ppos,
+ size = simple_read_from_buffer(buf, len, ppos,
file->private_data, size);
+ mutex_unlock(&data->lock);
+ return size;
}
static int u32_array_release(struct inode *inode, struct file *file)
@@ -643,6 +647,7 @@ struct dentry *debugfs_create_u32_array(const char *name,
umode_t mode,
data->array = array;
data->elements = elements;
+ mutex_init(&data->lock);
return debugfs_create_file(name, mode, parent, data,&u32_array_fops);
}
I was also able to reproduce the problem with pthread usage and
David's msleep trick.
[ 65.438698] BUG kmalloc-96 (Not tainted): Object already free
[ 65.534572] BUG kmalloc-96 (Not tainted): Poison overwritten
[ 2488.195923] BUG kmalloc-96 (Not tainted): Redzone overwritten
all the above BUG without David's array allocation in open patch
and Konrad's mutex patch.
(Both the patches tested separately)
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
