2007-12-19 06:06:20

by Reinette Chatre

Subject: [PATCH] ipw2200: prevent alloc of unspecified size on stack

if log_len is larger than 4K then we are killing the stack.
allocate on heap instead and limit size to what practically can
be used (PAGE_SIZE)

Is it possible for this to get into 2.6.24?

Signed-off-by: Reinette Chatre <[email protected]>
---
drivers/net/wireless/ipw2200.c | 13 ++++++++++++-
1 files changed, 12 insertions(+), 1 deletions(-)

diff --git a/drivers/net/wireless/ipw2200.c b/drivers/net/wireless/ipw2200.c
index 54f44e5..e19e83a 100644
--- a/drivers/net/wireless/ipw2200.c
+++ b/drivers/net/wireless/ipw2200.c
@@ -1233,9 +1233,19 @@ static ssize_t show_event_log(struct device *d,
{
struct ipw_priv *priv = dev_get_drvdata(d);
u32 log_len = ipw_get_event_log_len(priv);
- struct ipw_event log[log_len];
+ u32 log_size;
+ struct ipw_event *log;
u32 len = 0, i;

+ /* not using min() because of its strict type checking */
+ log_size = sizeof(*log) * log_len < PAGE_SIZE ?
+ sizeof(*log) * log_len : PAGE_SIZE;
+ log = kzalloc(log_size, GFP_KERNEL);
+ if (!log) {
+ IPW_ERROR("Unable to allocate memory for log\n");
+ return 0;
+ }
+ log_len = log_size / sizeof(*log);
ipw_capture_event_log(priv, log_len, log);

len += snprintf(buf + len, PAGE_SIZE - len, "%08X", log_len);
@@ -1244,6 +1254,7 @@ static ssize_t show_event_log(struct device *d,
"\n%08X%08X%08X",
log[i].time, log[i].event, log[i].data);
len += snprintf(buf + len, PAGE_SIZE - len, "\n");
+ kfree(log);
return len;
}

--
1.5.3.4

2007-12-19 06:35:30

by Al Viro

Subject: Re: [PATCH] ipw2200: prevent alloc of unspecified size on stack

On Tue, Dec 18, 2007 at 10:01:02PM -0800, Reinette Chatre wrote:
> + /* not using min() because of its strict type checking */
> + log_size = sizeof(*log) * log_len < PAGE_SIZE ?

PAGE_SIZE / sizeof(*log) > len ?

to be provably safe against wraparounds, if you really want to limit that
to PAGE_SIZE...

2007-12-19 06:23:30

by Zhu Yi

Subject: Re: [PATCH] ipw2200: prevent alloc of unspecified size on stack

On Tue, 2007-12-18 at 22:01 -0800, Reinette Chatre wrote:
> if log_len is larger than 4K then we are killing the stack.
> allocate on heap instead and limit size to what practically can
> be used (PAGE_SIZE)
>
> Is it possible for this to get into 2.6.24?
>
> Signed-off-by: Reinette Chatre <[email protected]>

ACK.

> ---
> + /* not using min() because of its strict type checking */
> + log_size = sizeof(*log) * log_len < PAGE_SIZE ?
> + sizeof(*log) * log_len : PAGE_SIZE;

A (u32) cast should work. But I don't think it's a big issue.

Thanks,
-yi

2007-12-19 07:28:40

by Zhu Yi

Subject: Re: [PATCH] ipw2200: prevent alloc of unspecified size on stack

On Wed, 2007-12-19 at 06:35 +0000, Al Viro wrote:
> to be provably safe against wraparounds, if you really want to limit
> that to PAGE_SIZE...

This is a sysfs read. We can only print PAGE_SIZE at most anyway.

Thanks,
-yi

2007-12-19 06:58:02

by Reinette Chatre

Subject: RE: [PATCH] ipw2200: prevent alloc of unspecified size on stack

On Tuesday, December 18, 2007 10:35 PM, Al Viro wrote:

> On Tue, Dec 18, 2007 at 10:01:02PM -0800, Reinette Chatre wrote:
>> + /* not using min() because of its strict type checking */
>> + log_size = sizeof(*log) * log_len < PAGE_SIZE ?
>
> PAGE_SIZE / sizeof(*log) > len ?
>
> to be provably safe against wraparounds, if you really want to limit
> that to PAGE_SIZE...

To cover this I reset log_len after allocating the memory:

+ }
+ log_len = log_size / sizeof(*log);
ipw_capture_event_log(priv, log_len, log);


If we use the original length then we are ok and log_len is just what it
was before. If we use PAGE_SIZE then log_len is reset to fit in the
amount of memory we allocated (PAGE_SIZE).

Is this what you meant?

Reinette