NOMMU: Lock i_mmap_mutex for access to the VMA prio list

Lock i_mmap_mutex for access to the VMA prio list to prevent concurrent
access.  Currently, certain parts of the mmap handling are protected by
the region mutex, but not all.

Reported-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Al Viro <viro@zeniv.linux.org.uk>
cc: stable@vger.kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 7 insertions, 0 deletions

diff --git a/mm/nommu.c b/mm/nommu.c
index b982290fd962..ee7e57ebef6a 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -696,9 +696,11 @@ static void add_vma_to_mm(struct mm_struct *mm, struct vm_area_struct *vma)
         if (vma->vm_file) {
                 mapping = vma->vm_file->f_mapping;
 
+                mutex_lock(&mapping->i_mmap_mutex);
                 flush_dcache_mmap_lock(mapping);
                 vma_prio_tree_insert(vma, &mapping->i_mmap);
                 flush_dcache_mmap_unlock(mapping);
+                mutex_unlock(&mapping->i_mmap_mutex);
         }
 
         /* add the VMA to the tree */
@@ -760,9 +762,11 @@ static void delete_vma_from_mm(struct vm_area_struct *vma)
         if (vma->vm_file) {
                 mapping = vma->vm_file->f_mapping;
 
+                mutex_lock(&mapping->i_mmap_mutex);
                 flush_dcache_mmap_lock(mapping);
                 vma_prio_tree_remove(vma, &mapping->i_mmap);
                 flush_dcache_mmap_unlock(mapping);
+                mutex_unlock(&mapping->i_mmap_mutex);
         }
 
         /* remove from the MM's tree and list */
@@ -2052,6 +2056,7 @@ int nommu_shrink_inode_mappings(struct inode *inode, size_t size,
         high = (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
 
         down_write(&nommu_region_sem);
+        mutex_lock(&inode->i_mapping->i_mmap_mutex);
 
         /* search for VMAs that fall within the dead zone */
         vma_prio_tree_foreach(vma, &iter, &inode->i_mapping->i_mmap,
@@ -2059,6 +2064,7 @@ int nommu_shrink_inode_mappings(struct inode *inode, size_t size,
                 /* found one - only interested if it's shared out of the page
                  * cache */
                 if (vma->vm_flags & VM_SHARED) {
+                        mutex_unlock(&inode->i_mapping->i_mmap_mutex);
                         up_write(&nommu_region_sem);
                         return -ETXTBSY; /* not quite true, but near enough */
                 }
@@ -2086,6 +2092,7 @@ int nommu_shrink_inode_mappings(struct inode *inode, size_t size,
                 }
         }
 
+        mutex_unlock(&inode->i_mapping->i_mmap_mutex);
         up_write(&nommu_region_sem);
         return 0;
 }