5.4-stable review patch. If anyone has any objections, please let me know.
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From: Lorenzo Stoakes lstoakes@gmail.com
[ Upstream commit 158978945f3173b8c1a88f8c5684a629736a57ac ]
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.
There is a delicate situation with cleanup paths assuming that a writable mapping must have occurred in circumstances where it may now not have. In order to ensure we do not accidentally mark a writable file unwritable by mistake, we explicitly track whether we have a writable mapping and unmap only if we do.
[lstoakes@gmail.com: do not set writable_file_mapping in inappropriate case] Link: https://lkml.kernel.org/r/c9eb4cc6-7db4-4c2b-838d-43a0b319a4f0@lucifer.local Link: https://bugzilla.kernel.org/show_bug.cgi?id=217238 Link: https://lkml.kernel.org/r/55e413d20678a1bb4c7cce889062bbb07b0df892.169711658... Signed-off-by: Lorenzo Stoakes lstoakes@gmail.com Reviewed-by: Jan Kara jack@suse.cz Cc: Alexander Viro viro@zeniv.linux.org.uk Cc: Andy Lutomirski luto@kernel.org Cc: Christian Brauner brauner@kernel.org Cc: Hugh Dickins hughd@google.com Cc: Matthew Wilcox (Oracle) willy@infradead.org Cc: Mike Kravetz mike.kravetz@oracle.com Cc: Muchun Song muchun.song@linux.dev Signed-off-by: Andrew Morton akpm@linux-foundation.org Cc: stable@vger.kernel.org [isaacmanjarres: added error handling to cleanup the work done by the mmap() callback and removed unused label.] Signed-off-by: Isaac J. Manjarres isaacmanjarres@google.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- mm/mmap.c | 22 ++++++++++++++-------- 1 file changed, 14 insertions(+), 8 deletions(-)
--- a/mm/mmap.c +++ b/mm/mmap.c @@ -1718,6 +1718,7 @@ unsigned long mmap_region(struct file *f { struct mm_struct *mm = current->mm; struct vm_area_struct *vma, *prev; + bool writable_file_mapping = false; int error; struct rb_node **rb_link, *rb_parent; unsigned long charged = 0; @@ -1785,11 +1786,6 @@ unsigned long mmap_region(struct file *f if (error) goto free_vma; } - if (is_shared_maywrite(vm_flags)) { - error = mapping_map_writable(file->f_mapping); - if (error) - goto allow_write_and_free_vma; - }
/* ->mmap() can change vma->vm_file, but must guarantee that * vma_link() below can deny write-access if VM_DENYWRITE is set @@ -1801,6 +1797,14 @@ unsigned long mmap_region(struct file *f if (error) goto unmap_and_free_vma;
+ if (vma_is_shared_maywrite(vma)) { + error = mapping_map_writable(file->f_mapping); + if (error) + goto close_and_free_vma; + + writable_file_mapping = true; + } + /* Can addr have changed?? * * Answer: Yes, several device drivers can do it in their @@ -1823,7 +1827,7 @@ unsigned long mmap_region(struct file *f vma_link(mm, vma, prev, rb_link, rb_parent); /* Once vma denies write, undo our temporary denial count */ if (file) { - if (is_shared_maywrite(vm_flags)) + if (writable_file_mapping) mapping_unmap_writable(file->f_mapping); if (vm_flags & VM_DENYWRITE) allow_write_access(file); @@ -1858,15 +1862,17 @@ out:
return addr;
+close_and_free_vma: + if (vma->vm_ops && vma->vm_ops->close) + vma->vm_ops->close(vma); unmap_and_free_vma: vma->vm_file = NULL; fput(file);
/* Undo any partial mapping done by a device driver. */ unmap_region(mm, vma, prev, vma->vm_start, vma->vm_end); - if (is_shared_maywrite(vm_flags)) + if (writable_file_mapping) mapping_unmap_writable(file->f_mapping); -allow_write_and_free_vma: if (vm_flags & VM_DENYWRITE) allow_write_access(file); free_vma: