Squashfs: Compute expected length from inode size rather than block length

Previously in squashfs_readpage() when copying data into the page
cache, it used the length of the datablock read from the filesystem
(after decompression).  However, if the filesystem has been corrupted
this data block may be short, which will leave pages unfilled.

The fix for this is to compute the expected number of bytes to copy
from the inode size, and use this to detect if the block is short.

Signed-off-by: Phillip Lougher <phillip@squashfs.org.uk>
Tested-by: Willy Tarreau <w@1wt.eu>
Cc: Анатолий Тросиненко <anatoly.trosinenko@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/squashfs/file.c

@@ -431,10 +431,9 @@ void squashfs_copy_cache(struct page *page, struct squashfs_cache_entry *buffer,
 }
 
 /* Read datablock stored packed inside a fragment (tail-end packed block) */
-static int squashfs_readpage_fragment(struct page *page)
+static int squashfs_readpage_fragment(struct page *page, int expected)
 {
 	struct inode *inode = page->mapping->host;
-	struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
 	struct squashfs_cache_entry *buffer = squashfs_get_fragment(inode->i_sb,
 		squashfs_i(inode)->fragment_block,
 		squashfs_i(inode)->fragment_size);
@@ -445,23 +444,16 @@ static int squashfs_readpage_fragment(struct page *page)
 			squashfs_i(inode)->fragment_block,
 			squashfs_i(inode)->fragment_size);
 	else
-		squashfs_copy_cache(page, buffer, i_size_read(inode) &
-			(msblk->block_size - 1),
+		squashfs_copy_cache(page, buffer, expected,
 			squashfs_i(inode)->fragment_offset);
 
 	squashfs_cache_put(buffer);
 	return res;
 }
 
-static int squashfs_readpage_sparse(struct page *page, int index, int file_end)
+static int squashfs_readpage_sparse(struct page *page, int expected)
 {
-	struct inode *inode = page->mapping->host;
-	struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
-	int bytes = index == file_end ?
-			(i_size_read(inode) & (msblk->block_size - 1)) :
-			 msblk->block_size;
-
-	squashfs_copy_cache(page, NULL, bytes, 0);
+	squashfs_copy_cache(page, NULL, expected, 0);
 	return 0;
 }
 
@@ -471,6 +463,9 @@ static int squashfs_readpage(struct file *file, struct page *page)
 	struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
 	int index = page->index >> (msblk->block_log - PAGE_SHIFT);
 	int file_end = i_size_read(inode) >> msblk->block_log;
+	int expected = index == file_end ?
+			(i_size_read(inode) & (msblk->block_size - 1)) :
+			 msblk->block_size;
 	int res;
 	void *pageaddr;
 
@@ -489,11 +484,11 @@ static int squashfs_readpage(struct file *file, struct page *page)
 			goto error_out;
 
 		if (bsize == 0)
-			res = squashfs_readpage_sparse(page, index, file_end);
+			res = squashfs_readpage_sparse(page, expected);
 		else
-			res = squashfs_readpage_block(page, block, bsize);
+			res = squashfs_readpage_block(page, block, bsize, expected);
 	} else
-		res = squashfs_readpage_fragment(page);
+		res = squashfs_readpage_fragment(page, expected);
 
 	if (!res)
 		return 0;

fs/squashfs/file_cache.c

@@ -20,7 +20,7 @@
 #include "squashfs.h"
 
 /* Read separately compressed datablock and memcopy into page cache */
-int squashfs_readpage_block(struct page *page, u64 block, int bsize)
+int squashfs_readpage_block(struct page *page, u64 block, int bsize, int expected)
 {
 	struct inode *i = page->mapping->host;
 	struct squashfs_cache_entry *buffer = squashfs_get_datablock(i->i_sb,
@@ -31,7 +31,7 @@ int squashfs_readpage_block(struct page *page, u64 block, int bsize)
 		ERROR("Unable to read page, block %llx, size %x\n", block,
 			bsize);
 	else
-		squashfs_copy_cache(page, buffer, buffer->length, 0);
+		squashfs_copy_cache(page, buffer, expected, 0);
 
 	squashfs_cache_put(buffer);
 	return res;

fs/squashfs/file_direct.c

@@ -21,10 +21,11 @@
 #include "page_actor.h"
 
 static int squashfs_read_cache(struct page *target_page, u64 block, int bsize,
-	int pages, struct page **page);
+	int pages, struct page **page, int bytes);
 
 /* Read separately compressed datablock directly into page cache */
-int squashfs_readpage_block(struct page *target_page, u64 block, int bsize)
+int squashfs_readpage_block(struct page *target_page, u64 block, int bsize,
+	int expected)
 
 {
 	struct inode *inode = target_page->mapping->host;
@@ -83,7 +84,7 @@ int squashfs_readpage_block(struct page *target_page, u64 block, int bsize)
 		 * using an intermediate buffer.
 		 */
 		res = squashfs_read_cache(target_page, block, bsize, pages,
-								page);
+							page, expected);
 		if (res < 0)
 			goto mark_errored;
 
@@ -95,6 +96,11 @@ int squashfs_readpage_block(struct page *target_page, u64 block, int bsize)
 	if (res < 0)
 		goto mark_errored;
 
+	if (res != expected) {
+		res = -EIO;
+		goto mark_errored;
+	}
+
 	/* Last page may have trailing bytes not filled */
 	bytes = res % PAGE_SIZE;
 	if (bytes) {
@@ -138,12 +144,12 @@ int squashfs_readpage_block(struct page *target_page, u64 block, int bsize)
 
 
 static int squashfs_read_cache(struct page *target_page, u64 block, int bsize,
-	int pages, struct page **page)
+	int pages, struct page **page, int bytes)
 {
 	struct inode *i = target_page->mapping->host;
 	struct squashfs_cache_entry *buffer = squashfs_get_datablock(i->i_sb,
 						 block, bsize);
-	int bytes = buffer->length, res = buffer->error, n, offset = 0;
+	int res = buffer->error, n, offset = 0;
 
 	if (res) {
 		ERROR("Unable to read page, block %llx, size %x\n", block,

fs/squashfs/squashfs.h

@@ -72,7 +72,7 @@ void squashfs_copy_cache(struct page *, struct squashfs_cache_entry *, int,
 				int);
 
 /* file_xxx.c */
-extern int squashfs_readpage_block(struct page *, u64, int);
+extern int squashfs_readpage_block(struct page *, u64, int, int);
 
 /* id.c */
 extern int squashfs_get_id(struct super_block *, unsigned int, unsigned int *);