ntfs: fix ntfs_test_inode and ntfs_init_locked_inode function type

Clang's Control Flow Integrity (CFI) is a security mechanism that can help
prevent JOP chains, deployed extensively in downstream kernels used in
Android.

Its deployment is hindered by mismatches in function signatures.  For this
case, we make callbacks match their intended function signature, and cast
parameters within them rather than casting the callback when passed as a
parameter.

When running `mount -t ntfs ...` we observe the following trace:

Call trace:
__cfi_check_fail+0x1c/0x24
name_to_dev_t+0x0/0x404
iget5_locked+0x594/0x5e8
ntfs_fill_super+0xbfc/0x43ec
mount_bdev+0x30c/0x3cc
ntfs_mount+0x18/0x24
mount_fs+0x1b0/0x380
vfs_kern_mount+0x90/0x398
do_mount+0x5d8/0x1a10
SyS_mount+0x108/0x144
el0_svc_naked+0x34/0x38

Signed-off-by: Luca Stefani <luca.stefani.ge1@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Tested-by: freak07 <michalechner92@googlemail.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>
Acked-by: Anton Altaparmakov <anton@tuxera.com>
Link: http://lkml.kernel.org/r/20200718112513.533800-1-luca.stefani.ge1@gmail.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/ntfs/dir.c

@@ -1504,7 +1504,7 @@ static int ntfs_dir_fsync(struct file *filp, loff_t start, loff_t end,
 	na.type = AT_BITMAP;
 	na.name = I30;
 	na.name_len = 4;
-	bmp_vi = ilookup5(vi->i_sb, vi->i_ino, (test_t)ntfs_test_inode, &na);
+	bmp_vi = ilookup5(vi->i_sb, vi->i_ino, ntfs_test_inode, &na);
 	if (bmp_vi) {
  		write_inode_now(bmp_vi, !datasync);
 		iput(bmp_vi);

fs/ntfs/inode.c

@@ -30,10 +30,10 @@
 /**
  * ntfs_test_inode - compare two (possibly fake) inodes for equality
  * @vi:		vfs inode which to test
- * @na:		ntfs attribute which is being tested with
+ * @data:	data which is being tested with
  *
  * Compare the ntfs attribute embedded in the ntfs specific part of the vfs
- * inode @vi for equality with the ntfs attribute @na.
+ * inode @vi for equality with the ntfs attribute @data.
  *
  * If searching for the normal file/directory inode, set @na->type to AT_UNUSED.
  * @na->name and @na->name_len are then ignored.
@@ -43,8 +43,9 @@
  * NOTE: This function runs with the inode_hash_lock spin lock held so it is not
  * allowed to sleep.
  */
-int ntfs_test_inode(struct inode *vi, ntfs_attr *na)
+int ntfs_test_inode(struct inode *vi, void *data)
 {
+	ntfs_attr *na = (ntfs_attr *)data;
 	ntfs_inode *ni;
 
 	if (vi->i_ino != na->mft_no)
@@ -72,9 +73,9 @@ int ntfs_test_inode(struct inode *vi, ntfs_attr *na)
 /**
  * ntfs_init_locked_inode - initialize an inode
  * @vi:		vfs inode to initialize
- * @na:		ntfs attribute which to initialize @vi to
+ * @data:	data which to initialize @vi to
  *
- * Initialize the vfs inode @vi with the values from the ntfs attribute @na in
+ * Initialize the vfs inode @vi with the values from the ntfs attribute @data in
  * order to enable ntfs_test_inode() to do its work.
  *
  * If initializing the normal file/directory inode, set @na->type to AT_UNUSED.
@@ -87,8 +88,9 @@ int ntfs_test_inode(struct inode *vi, ntfs_attr *na)
  * NOTE: This function runs with the inode->i_lock spin lock held so it is not
  * allowed to sleep. (Hence the GFP_ATOMIC allocation.)
  */
-static int ntfs_init_locked_inode(struct inode *vi, ntfs_attr *na)
+static int ntfs_init_locked_inode(struct inode *vi, void *data)
 {
+	ntfs_attr *na = (ntfs_attr *)data;
 	ntfs_inode *ni = NTFS_I(vi);
 
 	vi->i_ino = na->mft_no;
@@ -131,7 +133,6 @@ static int ntfs_init_locked_inode(struct inode *vi, ntfs_attr *na)
 	return 0;
 }
 
-typedef int (*set_t)(struct inode *, void *);
 static int ntfs_read_locked_inode(struct inode *vi);
 static int ntfs_read_locked_attr_inode(struct inode *base_vi, struct inode *vi);
 static int ntfs_read_locked_index_inode(struct inode *base_vi,
@@ -164,8 +165,8 @@ struct inode *ntfs_iget(struct super_block *sb, unsigned long mft_no)
 	na.name = NULL;
 	na.name_len = 0;
 
-	vi = iget5_locked(sb, mft_no, (test_t)ntfs_test_inode,
+	vi = iget5_locked(sb, mft_no, ntfs_test_inode,
-			(set_t)ntfs_init_locked_inode, &na);
+			ntfs_init_locked_inode, &na);
 	if (unlikely(!vi))
 		return ERR_PTR(-ENOMEM);
 
@@ -225,8 +226,8 @@ struct inode *ntfs_attr_iget(struct inode *base_vi, ATTR_TYPE type,
 	na.name = name;
 	na.name_len = name_len;
 
-	vi = iget5_locked(base_vi->i_sb, na.mft_no, (test_t)ntfs_test_inode,
+	vi = iget5_locked(base_vi->i_sb, na.mft_no, ntfs_test_inode,
-			(set_t)ntfs_init_locked_inode, &na);
+			ntfs_init_locked_inode, &na);
 	if (unlikely(!vi))
 		return ERR_PTR(-ENOMEM);
 
@@ -280,8 +281,8 @@ struct inode *ntfs_index_iget(struct inode *base_vi, ntfschar *name,
 	na.name = name;
 	na.name_len = name_len;
 
-	vi = iget5_locked(base_vi->i_sb, na.mft_no, (test_t)ntfs_test_inode,
+	vi = iget5_locked(base_vi->i_sb, na.mft_no, ntfs_test_inode,
-			(set_t)ntfs_init_locked_inode, &na);
+			ntfs_init_locked_inode, &na);
 	if (unlikely(!vi))
 		return ERR_PTR(-ENOMEM);
 

fs/ntfs/inode.h

@@ -253,9 +253,7 @@ typedef struct {
 	ATTR_TYPE type;
 } ntfs_attr;
 
-typedef int (*test_t)(struct inode *, void *);
+extern int ntfs_test_inode(struct inode *vi, void *data);
-
-extern int ntfs_test_inode(struct inode *vi, ntfs_attr *na);
 
 extern struct inode *ntfs_iget(struct super_block *sb, unsigned long mft_no);
 extern struct inode *ntfs_attr_iget(struct inode *base_vi, ATTR_TYPE type,

fs/ntfs/mft.c

@@ -958,7 +958,7 @@ bool ntfs_may_write_mft_record(ntfs_volume *vol, const unsigned long mft_no,
 		 * dirty code path of the inode dirty code path when writing
 		 * $MFT occurs.
 		 */
-		vi = ilookup5_nowait(sb, mft_no, (test_t)ntfs_test_inode, &na);
+		vi = ilookup5_nowait(sb, mft_no, ntfs_test_inode, &na);
 	}
 	if (vi) {
 		ntfs_debug("Base inode 0x%lx is in icache.", mft_no);
@@ -1019,7 +1019,7 @@ bool ntfs_may_write_mft_record(ntfs_volume *vol, const unsigned long mft_no,
 		vi = igrab(mft_vi);
 		BUG_ON(vi != mft_vi);
 	} else
-		vi = ilookup5_nowait(sb, na.mft_no, (test_t)ntfs_test_inode,
+		vi = ilookup5_nowait(sb, na.mft_no, ntfs_test_inode,
 				&na);
 	if (!vi) {
 		/*