mm: shift VM_GROWS* check from mmap_region() to do_mmap_pgoff()

mmap() doesn't allow the non-anonymous mappings with VM_GROWS* bit set.
In particular this means that mmap_region()->vma_merge(file, vm_flags)
must always fail if "vm_flags & VM_GROWS" is set incorrectly.

So it does not make sense to check VM_GROWS* after we already allocated
the new vma, the only caller, do_mmap_pgoff(), which can pass this flag
can do the check itself.

And this looks a bit more correct, mmap_region() already unmapped the
old mapping at this stage. But if mmap() is going to fail, it should
avoid do_munmap() if possible.

Note: we check VM_GROWS at the end to ensure that do_mmap_pgoff() won't
return EINVAL in the case when it currently returns another error code.

Many thanks to Hugh who nacked the buggy v1.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/mmap.c b/mm/mmap.c
index f5762ea..76cabd2 100644 (file)
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1049,6 +1049,8 @@ unsigned long do_mmap_pgoff(struct file *file, unsigned long addr,
 
                        if (!file->f_op || !file->f_op->mmap)
                                return -ENODEV;
+                       if (vm_flags & (VM_GROWSDOWN|VM_GROWSUP))
+                               return -EINVAL;
                        break;
 
                default:
@@ -1057,6 +1059,8 @@ unsigned long do_mmap_pgoff(struct file *file, unsigned long addr,
        } else {
                switch (flags & MAP_TYPE) {
                case MAP_SHARED:
+                       if (vm_flags & (VM_GROWSDOWN|VM_GROWSUP))
+                               return -EINVAL;
                        /*
                         * Ignore pgoff.
                         */
@@ -1271,11 +1275,7 @@ munmap_back:
        vma->vm_pgoff = pgoff;
        INIT_LIST_HEAD(&vma->anon_vma_chain);
 
-       error = -EINVAL;        /* when rejecting VM_GROWSDOWN|VM_GROWSUP */
-
        if (file) {
-               if (vm_flags & (VM_GROWSDOWN|VM_GROWSUP))
-                       goto free_vma;
                if (vm_flags & VM_DENYWRITE) {
                        error = deny_write_access(file);
                        if (error)