1 files changed, 40 insertions, 0 deletions

diff --git a/drivers/staging/android/ashmem.c b/drivers/staging/android/ashmem.c
index 74d497d39c5a..19b0cc5ea33f 100644
--- a/drivers/staging/android/ashmem.c
+++ b/drivers/staging/android/ashmem.c
@@ -95,6 +95,15 @@ static DEFINE_MUTEX(ashmem_mutex);
 static struct kmem_cache *ashmem_area_cachep __read_mostly;
 static struct kmem_cache *ashmem_range_cachep __read_mostly;
 
+/*
+ * A separate lockdep class for the backing shmem inodes to resolve the lockdep
+ * warning about the race between kswapd taking fs_reclaim before inode_lock
+ * and write syscall taking inode_lock and then fs_reclaim.
+ * Note that such race is impossible because ashmem does not support write
+ * syscalls operating on the backing shmem.
+ */
+static struct lock_class_key backing_shmem_inode_class;
+
 static inline unsigned long range_size(struct ashmem_range *range)
 {
 	return range->pgend - range->pgstart + 1;
@@ -351,8 +360,23 @@ static inline vm_flags_t calc_vm_may_flags(unsigned long prot)
 	       _calc_vm_trans(prot, PROT_EXEC,  VM_MAYEXEC);
 }
 
+static int ashmem_vmfile_mmap(struct file *file, struct vm_area_struct *vma)
+{
+	/* do not allow to mmap ashmem backing shmem file directly */
+	return -EPERM;
+}
+
+static unsigned long
+ashmem_vmfile_get_unmapped_area(struct file *file, unsigned long addr,
+				unsigned long len, unsigned long pgoff,
+				unsigned long flags)
+{
+	return current->mm->get_unmapped_area(file, addr, len, pgoff, flags);
+}
+
 static int ashmem_mmap(struct file *file, struct vm_area_struct *vma)
 {
+	static struct file_operations vmfile_fops;
 	struct ashmem_area *asma = file->private_data;
 	int ret = 0;
 
@@ -381,6 +405,7 @@ static int ashmem_mmap(struct file *file, struct vm_area_struct *vma)
 	if (!asma->file) {
 		char *name = ASHMEM_NAME_DEF;
 		struct file *vmfile;
+		struct inode *inode;
 
 		if (asma->name[ASHMEM_NAME_PREFIX_LEN] != '\0')
 			name = asma->name;
@@ -392,7 +417,22 @@ static int ashmem_mmap(struct file *file, struct vm_area_struct *vma)
 			goto out;
 		}
 		vmfile->f_mode |= FMODE_LSEEK;
+		inode = file_inode(vmfile);
+		lockdep_set_class(&inode->i_rwsem, &backing_shmem_inode_class);
 		asma->file = vmfile;
+		/*
+		 * override mmap operation of the vmfile so that it can't be
+		 * remapped which would lead to creation of a new vma with no
+		 * asma permission checks. Have to override get_unmapped_area
+		 * as well to prevent VM_BUG_ON check for f_ops modification.
+		 */
+		if (!vmfile_fops.mmap) {
+			vmfile_fops = *vmfile->f_op;
+			vmfile_fops.mmap = ashmem_vmfile_mmap;
+			vmfile_fops.get_unmapped_area =
+					ashmem_vmfile_get_unmapped_area;
+		}
+		vmfile->f_op = &vmfile_fops;
 	}
 	get_file(asma->file);