On Wed, 11 Jan 2012, Andrew Morton wrote:
diff --git a/mm/util.c b/mm/util.c
index 136ac4f..88bb4d4 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -91,7 +91,7 @@ void *memdup_user(const void __user *src, size_t len)
* cause pagefault, which makes it pointless to use GFP_NOFS
* or GFP_ATOMIC.
*/
- p = kmalloc_track_caller(len, GFP_KERNEL);
+ p = kmalloc_track_caller(len, GFP_KERNEL | __GFP_NOWARN);
if (!p)
return ERR_PTR(-ENOMEM);
There's nothing particularly special about memdup_user(): there are
many ways in which userspace can trigger GFP_KERNEL allocations.
The problem here (one which your patch carefully covers up) is that
ecryptfs_miscdev_write() is passing an unchecked userspace-provided
`count' direct into kmalloc(). This is a bit problematic for other
reasons: it gives userspace a way to trigger heavy reclaim activity and
perhaps even to trigger the oom-killer.
A better fix here would be to validate the incoming arg before using
it. Preferably by running ecryptfs_parse_packet_length() before taking
a copy of the data. That would require adding a small copy_from_user()
to peek at the message header.
Yup, right you are. I didn't think about the reclaim and oom issue. We
should add a big fat warning on top of memdup_user() to tell users to
check 'len' for sanity themselves. I think they're now fooled into
thinking memdup_user() automagically does the right thing.
Pekka
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