1 files changed, 15 insertions, 6 deletions

diff --git a/ipc/shm.c b/ipc/shm.c
index 01454796ba3c..19633b4a2350 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -219,7 +219,8 @@ static void shm_destroy(struct ipc_namespace *ns, struct shmid_kernel *shp)
         if (!is_file_hugepages(shm_file))
                 shmem_lock(shm_file, 0, shp->mlock_user);
         else if (shp->mlock_user)
-                user_shm_unlock(file_inode(shm_file)->i_size, shp->mlock_user);
+                user_shm_unlock(i_size_read(file_inode(shm_file)),
+                                shp->mlock_user);
         fput(shm_file);
         ipc_rcu_putref(shp, shm_rcu_free);
 }
@@ -1229,6 +1230,7 @@ SYSCALL_DEFINE1(shmdt, char __user *, shmaddr)
         int retval = -EINVAL;
 #ifdef CONFIG_MMU
         loff_t size = 0;
+        struct file *file;
         struct vm_area_struct *next;
 #endif
 
@@ -1245,7 +1247,8 @@ SYSCALL_DEFINE1(shmdt, char __user *, shmaddr)
          *   started at address shmaddr. It records it's size and then unmaps
          *   it.
          * - Then it unmaps all shm vmas that started at shmaddr and that
-         *   are within the initially determined size.
+         *   are within the initially determined size and that are from the
+         *   same shm segment from which we determined the size.
          * Errors from do_munmap are ignored: the function only fails if
          * it's called with invalid parameters or if it's called to unmap
          * a part of a vma. Both calls in this function are for full vmas,
@@ -1271,8 +1274,14 @@ SYSCALL_DEFINE1(shmdt, char __user *, shmaddr)
                 if ((vma->vm_ops == &shm_vm_ops) &&
                         (vma->vm_start - addr)/PAGE_SIZE == vma->vm_pgoff) {
 
-
-                        size = file_inode(vma->vm_file)->i_size;
+                        /*
+                         * Record the file of the shm segment being
+                         * unmapped.  With mremap(), someone could place
+                         * page from another segment but with equal offsets
+                         * in the range we are unmapping.
+                         */
+                        file = vma->vm_file;
+                        size = i_size_read(file_inode(vma->vm_file));
                         do_munmap(mm, vma->vm_start, vma->vm_end - vma->vm_start);
                         /*
                          * We discovered the size of the shm segment, so
@@ -1298,8 +1307,8 @@ SYSCALL_DEFINE1(shmdt, char __user *, shmaddr)
 
                 /* finding a matching vma now does not alter retval */
                 if ((vma->vm_ops == &shm_vm_ops) &&
-                        (vma->vm_start - addr)/PAGE_SIZE == vma->vm_pgoff)
-
+                    ((vma->vm_start - addr)/PAGE_SIZE == vma->vm_pgoff) &&
+                    (vma->vm_file == file))
                         do_munmap(mm, vma->vm_start, vma->vm_end - vma->vm_start);
                 vma = next;
         }