Commit:     900cf086fd2fbad07f72f4575449e0d0958f860f
Parent:     b1292b17dc03fcd90f3301974cea1b7c61371ba5
Author:     Jonathan Corbet <[EMAIL PROTECTED]>
AuthorDate: Mon Feb 11 16:17:33 2008 -0700
Committer:  Linus Torvalds <[EMAIL PROTECTED]>
CommitDate: Mon Feb 11 20:44:44 2008 -0800

    Be more robust about bad arguments 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
    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]>
    Signed-off-by: Linus Torvalds <[EMAIL PROTECTED]>
 mm/memory.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index e5628a5..717aa0e 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.
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