2.6.22-stable review patch. If anyone has any objections, please let us know. ------------------ From: Jonathan Corbet MAINLINE: 900cf086fd2fbad07f72f4575449e0d0958f860f 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 Signed-off-by: Linus Torvalds CC: Oliver Pinter Signed-off-by: Greg Kroah-Hartman --- mm/memory.c | 2 ++ 1 file changed, 2 insertions(+) --- a/mm/memory.c +++ b/mm/memory.c @@ -983,6 +983,8 @@ 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. -- -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/