[PATCH 1/3] NTFS: aops: Remove VLA usage

[Kees Cook]

In the quest to remove all stack VLA usage from the kernel[1], this
uses the maximum size needed on the stack and adds a sanity check for
robustness: index.block_size cannot be larger than PAGE_SIZE nor less
than NTFS_BLOCK_SIZE.

[1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@xxxxxxxxxxxxxx

Cc: Anton Altaparmakov <anton@xxxxxxxxxx>
Cc: linux-ntfs-dev@xxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
 fs/ntfs/aops.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/fs/ntfs/aops.c b/fs/ntfs/aops.c
index 3a2e509c77c5..58dadff3e0e0 100644
--- a/fs/ntfs/aops.c
+++ b/fs/ntfs/aops.c
@@ -926,7 +926,7 @@ static int ntfs_write_mst_block(struct page *page,
 	ntfs_volume *vol = ni->vol;
 	u8 *kaddr;
 	unsigned int rec_size = ni->itype.index.block_size;
-	ntfs_inode *locked_nis[PAGE_SIZE / rec_size];
+	ntfs_inode *locked_nis[PAGE_SIZE / NTFS_BLOCK_SIZE];
 	struct buffer_head *bh, *head, *tbh, *rec_start_bh;
 	struct buffer_head *bhs[MAX_BUF_PER_PAGE];
 	runlist_element *rl;
@@ -935,6 +935,9 @@ static int ntfs_write_mst_block(struct page *page,
 	bool sync, is_mft, page_is_dirty, rec_is_dirty;
 	unsigned char bh_size_bits;
 
+	if (WARN_ON(rec_size < NTFS_BLOCK_SIZE))
+		return -EINVAL;
+
 	ntfs_debug("Entering for inode 0x%lx, attribute type 0x%x, page index "
 			"0x%lx.", vi->i_ino, ni->type, page->index);
 	BUG_ON(!NInoNonResident(ni));
-- 
2.17.1