Messages in this thread | | | Date | Thu, 25 Nov 2004 17:45:09 -0200 | From | Marcelo Tosatti <> | Subject | Re: Memory leak in 2.4.27 kernel, using mmap raw packet sockets |
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On Fri, Nov 26, 2004 at 12:13:14AM +0100, Andrea Arcangeli wrote: > On Thu, Nov 25, 2004 at 03:12:42PM -0200, Marcelo Tosatti wrote: > > get_user_pages() bails out if ! VM_IO. > > > > Is that what you mean with "VM_IO enforcement" ? > > yes. It bails out if VM_IO is set (not ! clear ;) > > > I thought about the BUG() to catch potential offenders, but I was > > not sure if it was possible for a PG_reserved page to be part of VMA's > > which was being get_user_pages'd. > > Exactly, it's much safer to go with the real fix of fixing it in > get_user_pages. If something we should put a bugcheck there. > > > Now you tell me it is possible, and thats only the ZERO page. Fine. > > Yes, and the ZERO_PAGE is actually the _only_ reserved page we must > allow to go through. Every other reserved page must be discarded (or > kernel-crash with BUG_ON if Alan feels confortable with the VM_IO > enforcement).
Oh the VM_IO enforcement has been there for ages.
> > This is what you suggests plus some extra hopefully useful debugging > > > > > > --- memory.c.orig 2004-11-25 14:51:00.074508952 -0200 > > +++ memory.c 2004-11-25 15:08:38.026675776 -0200 > > @@ -454,8 +454,9 @@ > > int get_user_pages(struct task_struct *tsk, struct mm_struct *mm, unsigned long start, > > int len, int write, int force, struct page **pages, struct vm_area_struct **vmas) > > { > > - int i; > > + int i, s; > > unsigned int flags; > > + struct vm_area_struct *savevma = NULL; > > > > /* > > * Require read or write permissions. > > @@ -463,7 +464,7 @@ > > */ > > flags = write ? (VM_WRITE | VM_MAYWRITE) : (VM_READ | VM_MAYREAD); > > flags &= force ? (VM_MAYREAD | VM_MAYWRITE) : (VM_READ | VM_WRITE); > > - i = 0; > > + i = s = 0; > > > > do { > > struct vm_area_struct * vma; > > @@ -499,9 +500,13 @@ > > /* FIXME: call the correct function, > > * depending on the type of the found page > > */ > > - if (!pages[i] || PageReserved(pages[i])) > > - goto bad_page; > > - page_cache_get(pages[i]); > > + if (!pages[i] || PageReserved(pages[i])) { > > + if (pages[i] != ZERO_PAGE(start)) { > > + savevma = vma; > > + goto bad_page; > > + } > > + } else > > + page_cache_get(pages[i]); > > } > > if (vmas) > > vmas[i] = vma; > > @@ -520,9 +525,15 @@ > > */ > > bad_page: > > spin_unlock(&mm->page_table_lock); > > + s = i; > > while (i--) > > page_cache_release(pages[i]); > > - i = -EFAULT; > > + /* catch bad uses of PG_reserved on !VM_IO vma's */ > > + printk(KERN_ERR "get_user_pages PG_reserved page on" > > + "vma:%p flags:%lx page:%d\n", savevma, > > + savevma->flags, s); > > + BUG(); > > + i = -EFAULT; > > goto out; > > } > > Yes, however I wouldn't turn on the debugging code just in case some > driver forgets to set VM_IO and it doesn't use remap_page_range. There's > nothing fundamentally fatal in having a reserved page in a non VM_IO > vma (I mean, after fixing the above bit ;).
Sure, I'll comment the BUG() off during 2.4.29-rc.
How does that sound?
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