| Message ID | c814a3694f09896e4ec85cbca74069ea6174ebb6.1680560277.git.lstoakes@gmail.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | permit write-sealed memfd read-only shared mappings | expand |
On Mon 03-04-23 23:28:32, Lorenzo Stoakes wrote: > In order for a F_SEAL_WRITE sealed memfd mapping to have an opportunity to > clear VM_MAYWRITE, we must be able to invoke the appropriate vm_ops->mmap() > handler to do so. We would otherwise fail the mapping_map_writable() check > before we had the opportunity to avoid it. > > This patch moves this check after the call_mmap() invocation. Only memfd > actively denies write access causing a potential failure here (in > memfd_add_seals()), so there should be no impact on non-memfd cases. > > This patch makes the userland-visible change that MAP_SHARED, PROT_READ > mappings of an F_SEAL_WRITE sealed memfd mapping will now succeed. > > Signed-off-by: Lorenzo Stoakes <lstoakes@gmail.com> > --- > mm/mmap.c | 12 ++++++------ > 1 file changed, 6 insertions(+), 6 deletions(-) > > diff --git a/mm/mmap.c b/mm/mmap.c > index c96dcce90772..a166e9f3c474 100644 > --- a/mm/mmap.c > +++ b/mm/mmap.c > @@ -2596,17 +2596,17 @@ unsigned long mmap_region(struct file *file, unsigned long addr, > vma->vm_pgoff = pgoff; > > if (file) { > - if (is_shared_maywrite(vm_flags)) { > - error = mapping_map_writable(file->f_mapping); > - if (error) > - goto free_vma; > - } > - > vma->vm_file = get_file(file); > error = call_mmap(file, vma); > if (error) > goto unmap_and_free_vma; > > + if (vma_is_shared_maywrite(vma)) { > + error = mapping_map_writable(file->f_mapping); > + if (error) > + goto unmap_and_free_vma; Shouldn't we rather jump to close_and_free_vma? Honza
On Fri, Apr 21, 2023 at 11:06:28AM +0200, Jan Kara wrote: > On Mon 03-04-23 23:28:32, Lorenzo Stoakes wrote: > > In order for a F_SEAL_WRITE sealed memfd mapping to have an opportunity to > > clear VM_MAYWRITE, we must be able to invoke the appropriate vm_ops->mmap() > > handler to do so. We would otherwise fail the mapping_map_writable() check > > before we had the opportunity to avoid it. > > > > This patch moves this check after the call_mmap() invocation. Only memfd > > actively denies write access causing a potential failure here (in > > memfd_add_seals()), so there should be no impact on non-memfd cases. > > > > This patch makes the userland-visible change that MAP_SHARED, PROT_READ > > mappings of an F_SEAL_WRITE sealed memfd mapping will now succeed. > > > > Signed-off-by: Lorenzo Stoakes <lstoakes@gmail.com> > > --- > > mm/mmap.c | 12 ++++++------ > > 1 file changed, 6 insertions(+), 6 deletions(-) > > > > diff --git a/mm/mmap.c b/mm/mmap.c > > index c96dcce90772..a166e9f3c474 100644 > > --- a/mm/mmap.c > > +++ b/mm/mmap.c > > @@ -2596,17 +2596,17 @@ unsigned long mmap_region(struct file *file, unsigned long addr, > > vma->vm_pgoff = pgoff; > > > > if (file) { > > - if (is_shared_maywrite(vm_flags)) { > > - error = mapping_map_writable(file->f_mapping); > > - if (error) > > - goto free_vma; > > - } > > - > > vma->vm_file = get_file(file); > > error = call_mmap(file, vma); > > if (error) > > goto unmap_and_free_vma; > > > > + if (vma_is_shared_maywrite(vma)) { > > + error = mapping_map_writable(file->f_mapping); > > + if (error) > > + goto unmap_and_free_vma; > > Shouldn't we rather jump to close_and_free_vma? You're right, we may need to call vma->vm_ops->close() to match the ->mmap(). > > Honza > -- > Jan Kara <jack@suse.com> > SUSE Labs, CR
diff --git a/mm/mmap.c b/mm/mmap.c index c96dcce90772..a166e9f3c474 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -2596,17 +2596,17 @@ unsigned long mmap_region(struct file *file, unsigned long addr, vma->vm_pgoff = pgoff; if (file) { - if (is_shared_maywrite(vm_flags)) { - error = mapping_map_writable(file->f_mapping); - if (error) - goto free_vma; - } - vma->vm_file = get_file(file); error = call_mmap(file, vma); if (error) goto unmap_and_free_vma; + if (vma_is_shared_maywrite(vma)) { + error = mapping_map_writable(file->f_mapping); + if (error) + goto unmap_and_free_vma; + } + /* * Expansion is handled above, merging is handled below. * Drivers should not alter the address of the VMA.
In order for a F_SEAL_WRITE sealed memfd mapping to have an opportunity to clear VM_MAYWRITE, we must be able to invoke the appropriate vm_ops->mmap() handler to do so. We would otherwise fail the mapping_map_writable() check before we had the opportunity to avoid it. This patch moves this check after the call_mmap() invocation. Only memfd actively denies write access causing a potential failure here (in memfd_add_seals()), so there should be no impact on non-memfd cases. This patch makes the userland-visible change that MAP_SHARED, PROT_READ mappings of an F_SEAL_WRITE sealed memfd mapping will now succeed. Signed-off-by: Lorenzo Stoakes <lstoakes@gmail.com> --- mm/mmap.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-)