Messages in this thread | | | Date | Thu, 12 Jan 2012 09:12:12 +0200 (EET) | From | Pekka Enberg <> | Subject | Re: [PATCH] mm: Don't warn if memdup_user fails |
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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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