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authorJonathan Corbet <corbet@lwn.net>2008-02-11 16:17:33 -0700
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2008-02-11 20:44:44 -0800
commit900cf086fd2fbad07f72f4575449e0d0958f860f (patch)
tree9d48ca4463111c074ea8688fd8041115387156e1
parentb1292b17dc03fcd90f3301974cea1b7c61371ba5 (diff)
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 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>
-rw-r--r--mm/memory.c2
1 files changed, 2 insertions, 0 deletions
diff --git a/mm/memory.c b/mm/memory.c
index e5628a5fd67..717aa0e3be2 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.