From 8079ffa0e18baaf2940e52e0c118eef420a473a4 Mon Sep 17 00:00:00 2001 From: Roland Dreier Date: Fri, 6 Jun 2008 21:38:37 -0700 Subject: [PATCH] IB/umem: Avoid sign problems when demoting npages to integer On a 64-bit architecture, if ib_umem_get() is called with a size value that is so big that npages is negative when cast to int, then the length of the page list passed to get_user_pages(), namely min_t(int, npages, PAGE_SIZE / sizeof (struct page *)) will be negative, and get_user_pages() will immediately return 0 (at least since 900cf086, "Be more robust about bad arguments in get_user_pages()"). This leads to an infinite loop in ib_umem_get(), since the code boils down to: while (npages) { ret = get_user_pages(...); npages -= ret; } Fix this by taking the minimum as unsigned longs, so that the value of npages is never truncated. The impact of this bug isn't too severe, since the value of npages is checked against RLIMIT_MEMLOCK, so a process would need to have an astronomical limit or have CAP_IPC_LOCK to be able to trigger this, and such a process could already cause lots of mischief. But it does let buggy userspace code cause a kernel lock-up; for example I hit this with code that passes a negative value into a memory registartion function where it is promoted to a huge u64 value. Cc: Signed-off-by: Roland Dreier --- drivers/infiniband/core/umem.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/infiniband/core/umem.c b/drivers/infiniband/core/umem.c index fe78f7d2509..a1768dbb072 100644 --- a/drivers/infiniband/core/umem.c +++ b/drivers/infiniband/core/umem.c @@ -150,7 +150,7 @@ struct ib_umem *ib_umem_get(struct ib_ucontext *context, unsigned long addr, ret = 0; while (npages) { ret = get_user_pages(current, current->mm, cur_base, - min_t(int, npages, + min_t(unsigned long, npages, PAGE_SIZE / sizeof (struct page *)), 1, !umem->writable, page_list, vma_list); -- 2.41.1