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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: Kees Cook <keescook@chromium.org>
Cc: Anton Altaparmakov <anton@tuxera.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Kees Cook 2018-08-17 15:44:11 -07:00 committed by Linus Torvalds
parent ac4ecf968a
commit 2c27ce9150
1 changed files with 16 additions and 12 deletions
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28
fs/ntfs/compress.c
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@ -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 @@ int ntfs_read_compressed_block(struct page *page)
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 @@ int ntfs_read_compressed_block(struct page *page)
/* 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 @@ int ntfs_read_compressed_block(struct page *page)
}
}
kfree(pages);
kfree(completed_pages);
return -EIO;
}