Commit 2c27ce91 authored by Kees Cook's avatar Kees Cook Committed by Linus Torvalds
Browse files

ntfs: decompress: remove VLA usage 

In the quest to remove all stack VLA usage from the kernel[1], this
moves the stack buffer used during decompression to be allocated
externally.

The existing "dest_max_index" used in the VLA is bounded by cb_max_page.
cb_max_page is bounded by max_page, and max_page is bounded by nr_pages.
Since nr_pages is used for the "pages" allocation, it can similarly be
used for the "completed_pages" allocation and passed into the
decompression function.  The error paths are updated to free the new
allocation.

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

Link: http://lkml.kernel.org/r/20180626172909.41453-3-keescook@chromium.org


Signed-off-by: default avatarKees Cook <keescook@chromium.org>
Cc: Anton Altaparmakov <anton@tuxera.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent ac4ecf96

fs/ntfs/compress.c

+16 −12
Original line number Diff line number Diff line
@@ -128,6 +128,7 @@ static inline void handle_bounds_compressed_page(struct page *page, 
/**

 * ntfs_decompress - decompress a compression block into an array of pages

 * @dest_pages:		destination array of pages

 * @completed_pages:	scratch space to track completed pages

 * @dest_index:		current index into @dest_pages (IN/OUT)

 * @dest_ofs:		current offset within @dest_pages[@dest_index] (IN/OUT)

 * @dest_max_index:	maximum index into @dest_pages (IN)
@@ -162,10 +163,10 @@ static inline void handle_bounds_compressed_page(struct page *page, 
 * Note to hackers: This function may not sleep until it has finished accessing

 * the compression block @cb_start as it is a per-CPU buffer.

 */

static int ntfs_decompress(struct page *dest_pages[], int *dest_index,

		int *dest_ofs, const int dest_max_index, const int dest_max_ofs,

		const int xpage, char *xpage_done, u8 *const cb_start,

		const u32 cb_size, const loff_t i_size,

static int ntfs_decompress(struct page *dest_pages[], int completed_pages[],

		int *dest_index, int *dest_ofs, const int dest_max_index,

		const int dest_max_ofs, const int xpage, char *xpage_done,

		u8 *const cb_start, const u32 cb_size, const loff_t i_size,

		const s64 initialized_size)

{

	/*
@@ -190,9 +191,6 @@ static int ntfs_decompress(struct page *dest_pages[], int *dest_index, 
	/* Variables for tag and token parsing. */

	u8 tag;			/* Current tag. */

	int token;		/* Loop counter for the eight tokens in tag. */



	/* Need this because we can't sleep, so need two stages. */

	int completed_pages[dest_max_index - *dest_index + 1];

	int nr_completed_pages = 0;



	/* Default error code. */
@@ -516,6 +514,7 @@ int ntfs_read_compressed_block(struct page *page) 
	unsigned int cb_clusters, cb_max_ofs;

	int block, max_block, cb_max_page, bhs_size, nr_bhs, err = 0;

	struct page **pages;

	int *completed_pages;

	unsigned char xpage_done = 0;



	ntfs_debug("Entering, page->index = 0x%lx, cb_size = 0x%x, nr_pages = "
@@ -528,14 +527,16 @@ int ntfs_read_compressed_block(struct page *page) 
	BUG_ON(ni->name_len);



	pages = kmalloc_array(nr_pages, sizeof(struct page *), GFP_NOFS);

	completed_pages = kmalloc_array(nr_pages + 1, sizeof(int), GFP_NOFS);



	/* Allocate memory to store the buffer heads we need. */

	bhs_size = cb_size / block_size * sizeof(struct buffer_head *);

	bhs = kmalloc(bhs_size, GFP_NOFS);



	if (unlikely(!pages || !bhs)) {

	if (unlikely(!pages || !bhs || !completed_pages)) {

		kfree(bhs);

		kfree(pages);

		kfree(completed_pages);

		unlock_page(page);

		ntfs_error(vol->sb, "Failed to allocate internal buffers.");

		return -ENOMEM;
@@ -562,6 +563,7 @@ int ntfs_read_compressed_block(struct page *page) 
	if (xpage >= max_page) {

		kfree(bhs);

		kfree(pages);

		kfree(completed_pages);

		zero_user(page, 0, PAGE_SIZE);

		ntfs_debug("Compressed read outside i_size - truncated?");

		SetPageUptodate(page);
@@ -854,10 +856,10 @@ lock_retry_remap: 
		unsigned int prev_cur_page = cur_page;



		ntfs_debug("Found compressed compression block.");

		err = ntfs_decompress(pages, &cur_page, &cur_ofs,

				cb_max_page, cb_max_ofs, xpage, &xpage_done,

				cb_pos,	cb_size - (cb_pos - cb), i_size,

				initialized_size);

		err = ntfs_decompress(pages, completed_pages, &cur_page,

				&cur_ofs, cb_max_page, cb_max_ofs, xpage,

				&xpage_done, cb_pos, cb_size - (cb_pos - cb),

				i_size, initialized_size);

		/*

		 * We can sleep from now on, lock already dropped by

		 * ntfs_decompress().
@@ -912,6 +914,7 @@ lock_retry_remap: 


	/* We no longer need the list of pages. */

	kfree(pages);

	kfree(completed_pages);



	/* If we have completed the requested page, we return success. */

	if (likely(xpage_done))
@@ -956,5 +959,6 @@ err_out: 
		}

	}

	kfree(pages);

	kfree(completed_pages);

	return -EIO;

}

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