Messages in this thread |  | | From | Namhyung Kim <> | Subject | Re: [PATCH 12/13] tracing/uprobes: Add more fetch functions | Date | Tue, 05 Nov 2013 11:19:49 +0900 |
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Hi Steve,
On Mon, 4 Nov 2013 12:17:06 -0500, Steven Rostedt wrote: > On Mon, 4 Nov 2013 17:44:31 +0100 > Oleg Nesterov <oleg@redhat.com> wrote: > >> On 11/04, Namhyung Kim wrote: >> > >> > On Thu, 31 Oct 2013 19:22:18 +0100, Oleg Nesterov wrote: >> > > On 10/29, Namhyung Kim wrote: >> > >> >> > >> +static void __user *get_user_vaddr(unsigned long addr, struct trace_uprobe *tu) >> > >> +{ >> > >> + unsigned long pgoff = addr >> PAGE_SHIFT; >> > >> + struct vm_area_struct *vma; >> > >> + struct address_space *mapping; >> > >> + unsigned long vaddr = 0; >> > >> + >> > >> + if (tu == NULL) { >> > >> + /* A NULL tu means that we already got the vaddr */ >> > >> + return (void __force __user *) addr; >> > >> + } >> > >> + >> > >> + mapping = tu->inode->i_mapping; >> > >> + >> > >> + mutex_lock(&mapping->i_mmap_mutex); >> > >> + vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) { >> > >> + if (vma->vm_mm != current->mm) >> > >> + continue; >> > >> + if (!(vma->vm_flags & VM_READ)) >> > >> + continue; >> > >> + >> > >> + vaddr = offset_to_vaddr(vma, addr); >> > >> + break; >> > >> + } >> > >> + mutex_unlock(&mapping->i_mmap_mutex); >> > >> + >> > >> + WARN_ON_ONCE(vaddr == 0); >> > > >> > > Hmm. But unless I missed something this "addr" passed as an argument can >> > > be wrong? And if nothing else this or another thread can unmap the vma? >> > >> > You mean WARN_ON_ONCE here is superfluous? I admit that it should >> > protect concurrent vma [un]mappings. Please see my reply in other >> > thread for a new approach. >> >> Whatever we do this address can be unmapped. For example, just because of >> @invalid_address passed to trace_uprobe.c. >> >> We do not really care, copy_from_user() should fail. But we should not >> WARN() in this case. >> > > I agree, the WARN_ON_ONCE() above looks like it's uncalled for. > WARN()ings should only be used when an anomaly in the kernel logic is > detected. Can this trigger on bad input from user space, or something > else that userspace does? (a race with unmapping memory?). If so, error > out to the user process, but do not call any of the WARN() functions.
Will do. Thanks for the explanation.
Thanks, Namhyung
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