Messages in this thread | | | Date | Fri, 8 Nov 2013 17:24:15 +0100 | From | Oleg Nesterov <> | Subject | Re: [PATCH 1/1] uprobes: Fix the memory out of bound overwrite in copy_insn() |
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On 11/07, Oleg Nesterov wrote: > > Note: we do not care if offset + size > i_size, the users of > arch_uprobe->insn can't know how many bytes were actually copied > anyway. But perhaps this needs more changes.
I guess this not is not very clear...
What I tried to say. Suppose that offset == 0 and i_size = 1. In this case we still copy MAX_UINSN_BYTES into arch.insn because the task gets the same page after page fault anyway, and we can't inform arch_uprobe_analyze_insn() that we have only read 1 byte. So this doesn't matter.
I changed this as follows:
Note: we do not care if we read extra bytes after inode->i_size if we got the valid page. This is fine because the task gets the same page after page-fault, and arch_uprobe_analyze_insn() can't know how how many bytes were actually read anyway.
I also moved the comment up, before the main loop.
Srikar, I am going to add this to my tree unless you object now. I verified that this indeed fixes the crash and the code looks "obviously correct, see below.
Oleg.
static int __copy_insn(struct address_space *mapping, struct file *filp, void *insn, int nbytes, loff_t offset) { struct page *page;
if (!mapping->a_ops->readpage) return -EIO; /* * Ensure that the page that has the original instruction is * populated and in page-cache. */ page = read_mapping_page(mapping, offset >> PAGE_CACHE_SHIFT, filp); if (IS_ERR(page)) return PTR_ERR(page);
copy_from_page(page, offset, insn, nbytes); page_cache_release(page);
return 0; }
static int copy_insn(struct uprobe *uprobe, struct file *filp) { struct address_space *mapping = uprobe->inode->i_mapping; loff_t offs = uprobe->offset; void *insn = uprobe->arch.insn; int size = MAX_UINSN_BYTES; int len, err = -EIO;
/* Copy only available bytes, -EIO if nothing was read */ do { if (offs >= i_size_read(uprobe->inode)) break;
len = min_t(int, size, PAGE_SIZE - (offs & ~PAGE_MASK)); err = __copy_insn(mapping, filp, insn, len, offs); if (err) break;
insn += len; offs += len; size -= len; } while (size);
return err; }
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