for stable (.22 .23 .24) ? git id in mainline: 900cf086fd2fbad07f72f4575449e0d0958f860f
-- tested in: http://repo.or.cz/w/linux-2.6.22.y-op.git testing On 2/12/08, Jonathan Corbet <[EMAIL PROTECTED]> wrote: > Avoid buffer overflows in get_user_pages() > > 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 <[EMAIL PROTECTED]> > > diff --git a/mm/memory.c b/mm/memory.c > index e5628a5..7f50fd8 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -989,6 +989,8 @@ int get_user_pages(struct task_struct *tsk, struct > mm_struct *mm, > 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 [EMAIL PROTECTED] > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ > -- Thanks, Oliver -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
