Message ID | 20221018191613.4133459-1-Liam.Howlett@oracle.com (mailing list archive) |
---|---|
State | New |
Headers | show |
Series | mm/mmap: Fix MAP_FIXED address return on VMA merge | expand |
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? Do we want to add some more tests for such scenarios? > 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@huawei.com> > Cc: David Hildenbrand <david@redhat.com> > Cc: Jason Gunthorpe <jgg@nvidia.com> > Cc: Matthew Wilcox <willy@infradead.org> > Link: https://lore.kernel.org/all/Y06yk66SKxlrwwfb@lakrids/ > Link: https://lore.kernel.org/all/20201203085350.22624-1-liuzixian4@huawei.com/ > Fixes: 4dd1b84140c1 (mm/mmap: use advanced maple tree API for mmap_region()) > Reported-by: Mark Rutland <mark.rutland@arm.com> > Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com> > --- > 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. Why not "if (WARN_ON_ONCE)" ?
On Tue, Oct 18, 2022 at 09:27:11PM +0200, David Hildenbrand wrote: > > + 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. It's something that a device driver can trigger. So if userspace calls mmap(MAP_FIXED) and the driver decides to overwrite the vma->vm_start, it'll trigger. I think WARN_ON() is the right choice. > Why not "if (WARN_ON_ONCE)" ? Because by it's nature it's not going to trigger a bajillion times in quick succession.
* David Hildenbrand <david@redhat.com> [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@huawei.com> > > Cc: David Hildenbrand <david@redhat.com> > > Cc: Jason Gunthorpe <jgg@nvidia.com> > > Cc: Matthew Wilcox <willy@infradead.org> > > Link: https://lore.kernel.org/all/Y06yk66SKxlrwwfb@lakrids/ > > Link: https://lore.kernel.org/all/20201203085350.22624-1-liuzixian4@huawei.com/ > > Fixes: 4dd1b84140c1 (mm/mmap: use advanced maple tree API for mmap_region()) > > Reported-by: Mark Rutland <mark.rutland@arm.com> > > Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com> > > --- > > 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
>>> 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. WARN_ON_ONCE() can also be used in conditionals if that's what you were concerned about, but ... > >> >> 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. .. I think the assumption really is that we won't see (m)any these calls. And if we do, it's a bad bad driver. So WARN_ON() might be just fine. If this would be easy to trigger by any user space, WARN* would have been the wrong choice, that's why I was asking.
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; + } mas_reset(&mas); /* @@ -2654,7 +2654,6 @@ unsigned long mmap_region(struct file *file, unsigned long addr, vm_area_free(vma); vma = merge; /* Update vm_flags to pick up the change. */ - addr = vma->vm_start; vm_flags = vma->vm_flags; goto unmap_writable; }
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. 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@huawei.com> Cc: David Hildenbrand <david@redhat.com> Cc: Jason Gunthorpe <jgg@nvidia.com> Cc: Matthew Wilcox <willy@infradead.org> Link: https://lore.kernel.org/all/Y06yk66SKxlrwwfb@lakrids/ Link: https://lore.kernel.org/all/20201203085350.22624-1-liuzixian4@huawei.com/ Fixes: 4dd1b84140c1 (mm/mmap: use advanced maple tree API for mmap_region()) Reported-by: Mark Rutland <mark.rutland@arm.com> Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com> --- mm/mmap.c | 15 +++++++-------- 1 file changed, 7 insertions(+), 8 deletions(-)