Messages in this thread | | | Date | Thu, 2 Nov 2017 18:46:12 +0000 | From | Al Viro <> | Subject | Re: [PATCH 1/1] Fix: vmw_vmci driver get_user_pages_fast error handling |
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On Tue, Oct 31, 2017 at 07:00:38PM -0400, Mathieu Desnoyers wrote: > Comparing a signed return value against an unsigned num_pages > field performs the comparison as "unsigned", and therefore mistakenly > considers get_user_pages_fast() errors as success.
It's worse than that - if you look into the code in question you'll see pr_debug("get_user_pages_fast(produce) failed (retval=%d)", retval); qp_release_pages(produce_q->kernel_if->u.h.header_page, retval, false); err = VMCI_ERROR_NO_MEM; goto out; with static void qp_release_pages(struct page **pages, u64 num_pages, bool dirty) { int i;
for (i = 0; i < num_pages; i++) { if (dirty) set_page_dirty(pages[i]);
put_page(pages[i]); pages[i] = NULL; } }
Now, guess what'll happen if you get there with retval being negative? AFAICS, the right fix is something along the lines of if (retval != produce_q->kernel_if->num_pages) { pr_debug("get_user_pages_fast(produce) failed (retval=%d)", retval); if (retval > 0) qp_release_pages(produce_q->kernel_if->u.h.header_page, retval, false); err = VMCI_ERROR_NO_MEM; goto out; } and similar for the second caller. Objections?
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