* David Hildenbrand <david@xxxxxxxxxx> [221018 15:27]: > On 18.10.22 21:17, Liam Howlett wrote: > > mmap should return the start address of newly mapped area when > > successful. On a successful merge of a VMA, the return address was > > changed and thus was violating that expectation from userspace. > > > > Just wondering, do we have a simple user space reproducer / test? Not today, no. > > Do we want to add some more tests for such scenarios? Yes, I will code something up for LTP. > > > This is a restoration of functionality provided by 309d08d9b3a3 > > (mm/mmap.c: fix mmap return value when vma is merged after call_mmap()). > > For completeness of fixing MAP_FIXED, implement the comments from the > > previous discussion to never update the address and fail if the address > > changes. Leaving the error as a WARN_ON() to avoid crashing the kernel. > > > > Cc: Liu Zixian <liuzixian4@xxxxxxxxxx> > > Cc: David Hildenbrand <david@xxxxxxxxxx> > > Cc: Jason Gunthorpe <jgg@xxxxxxxxxx> > > Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx> > > Link: https://lore.kernel.org/all/Y06yk66SKxlrwwfb@lakrids/ > > Link: https://lore.kernel.org/all/20201203085350.22624-1-liuzixian4@xxxxxxxxxx/ > > Fixes: 4dd1b84140c1 (mm/mmap: use advanced maple tree API for mmap_region()) > > Reported-by: Mark Rutland <mark.rutland@xxxxxxx> > > Signed-off-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx> > > --- > > mm/mmap.c | 15 +++++++-------- > > 1 file changed, 7 insertions(+), 8 deletions(-) > > > > diff --git a/mm/mmap.c b/mm/mmap.c > > index 42cd2c260898..22010e13f1a1 100644 > > --- a/mm/mmap.c > > +++ b/mm/mmap.c > > @@ -2625,14 +2625,14 @@ unsigned long mmap_region(struct file *file, unsigned long addr, > > if (error) > > goto unmap_and_free_vma; > > - /* Can addr have changed?? > > - * > > - * Answer: Yes, several device drivers can do it in their > > - * f_op->mmap method. -DaveM > > + /* > > + * Expansion is handled above, merging is handled below. > > + * Drivers should not alter the address of the VMA. > > */ > > - WARN_ON_ONCE(addr != vma->vm_start); > > - > > - addr = vma->vm_start; > > + if (WARN_ON((addr != vma->vm_start))) { > > + error = -EINVAL; > > + goto close_and_free_vma; > > + } > > If this is something that user space can trigger, WARN_* is the wrong > choice. But what I understand from the comment change is that this must not > happen at that point unless there is a real issue. The VMA start address could be changed in call_mmap() which is a driver call. I guess someone could write a driver to mmap by a users action? I don't think it can be reached other ways. In any case, I'm changing a WARN_ON_ONCE() to a WARN_ON() and undoing the badness instead of marching forwards. > > Why not "if (WARN_ON_ONCE)" ? I was thinking it was harder to ignore if it happen more frequently? There isn't a driver that does this now, but I'm not picky over which variant to call. Thanks, Liam
