Messages in this thread Patch in this message | | | Date | Fri, 22 Feb 2008 16:17:36 -0800 | From | Greg KH <> | Subject | [patch 7/8] Be more robust about bad arguments in get_user_pages() |
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2.6.23-stable review patch. If anyone has any objections, please let us know.
------------------ From: Jonathan Corbet <corbet@lwn.net>
patch 900cf086fd2fbad07f72f4575449e0d0958f860f in mainline.
So I spent a while pounding my head against my monitor trying to figure out the vmsplice() vulnerability - how could a failure to check for *read* access turn into a root exploit? It turns out that it's a buffer overflow problem which is made easy by the way get_user_pages() is coded.
In particular, "len" is a signed int, and it is only checked at the *end* of a do {} while() loop. So, if it is passed in as zero, the loop will execute once and decrement len to -1. At that point, the loop will proceed until the next invalid address is found; in the process, it will likely overflow the pages array passed in to get_user_pages().
I think that, if get_user_pages() has been asked to grab zero pages, that's what it should do. Thus this patch; it is, among other things, enough to block the (already fixed) root exploit and any others which might be lurking in similar code. I also think that the number of pages should be unsigned, but changing the prototype of this function probably requires some more careful review.
Signed-off-by: Jonathan Corbet <corbet@lwn.net> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
--- mm/memory.c | 2 ++ 1 file changed, 2 insertions(+)
--- a/mm/memory.c +++ b/mm/memory.c @@ -981,6 +981,8 @@ int get_user_pages(struct task_struct *t int i; unsigned int vm_flags; + if (len <= 0) + return 0; /* * Require read or write permissions. * If 'force' is set, we only require the "MAY" flags. --
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