On Wed, May 17, 2023 at 11:04:07AM -0400, Peter Xu wrote: > It seems vma merging with uffd paths is broken with either > register/unregister, where right now we can feed wrong parameters to > vma_merge() and it's found by recent patch which moved asserts upwards in > vma_merge() by Lorenzo Stoakes: > > https://lore.kernel.org/all/ZFunF7DmMdK05MoF@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/ > > The problem is in the current code base we didn't fixup "prev" for the case > where "start" address can be within the "prev" vma section. In that case > we should have "prev" points to the current vma rather than the previous > one when feeding to vma_merge(). This doesn't seem quite correct, perhaps - "where start is contained within vma but not clamped to its start. We need to convert this into case 4 which permits subdivision of prev by assigning vma to prev. As we loop, each subsequent VMA will be clamped to the start." > > This patch will eliminate the report and make sure vma_merge() calls will > become legal again. > > One thing to mention is that the "Fixes: 29417d292bd0" below is there only > to help explain where the warning can start to trigger, the real commit to > fix should be 69dbe6daf104. Commit 29417d292bd0 helps us to identify the > issue, but unfortunately we may want to keep it in Fixes too just to ease > kernel backporters for easier tracking. > > Cc: Lorenzo Stoakes <lstoakes@xxxxxxxxx> > Cc: Mike Rapoport (IBM) <rppt@xxxxxxxxxx> > Cc: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx> > Reported-by: Mark Rutland <mark.rutland@xxxxxxx> > Fixes: 29417d292bd0 ("mm/mmap/vma_merge: always check invariants") > Fixes: 69dbe6daf104 ("userfaultfd: use maple tree iterator to iterate VMAs") > Closes: https://lore.kernel.org/all/ZFunF7DmMdK05MoF@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/ > Cc: linux-stable <stable@xxxxxxxxxxxxxxx> > Signed-off-by: Peter Xu <peterx@xxxxxxxxxx> > --- > fs/userfaultfd.c | 5 +++++ > 1 file changed, 5 insertions(+) > > diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c > index 0fd96d6e39ce..17c8c345dac4 100644 > --- a/fs/userfaultfd.c > +++ b/fs/userfaultfd.c > @@ -1459,6 +1459,8 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx, > > vma_iter_set(&vmi, start); > prev = vma_prev(&vmi); > + if (vma->vm_start < start) > + prev = vma; > > ret = 0; > for_each_vma_range(vmi, vma, end) { > @@ -1625,6 +1627,9 @@ static int userfaultfd_unregister(struct userfaultfd_ctx *ctx, > > vma_iter_set(&vmi, start); > prev = vma_prev(&vmi); > + if (vma->vm_start < start) > + prev = vma; > + > ret = 0; > for_each_vma_range(vmi, vma, end) { > cond_resched(); > -- > 2.39.1 > Other than that looks good:- Reviewed-by: Lorenzo Stoakes <lstoakes@xxxxxxxxx>
