+ squashfs-fix-variable-overflow-in-squashfs_readpage_block.patch added to mm-hotfixes-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: Squashfs: fix variable overflow in squashfs_readpage_block
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     squashfs-fix-variable-overflow-in-squashfs_readpage_block.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/squashfs-fix-variable-overflow-in-squashfs_readpage_block.patch

This patch will later appear in the mm-hotfixes-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Phillip Lougher <phillip@squashfs.org.uk>
Subject: Squashfs: fix variable overflow in squashfs_readpage_block
Date: Mon, 21 Oct 2024 00:22:00 +0100

Syzbot reports a slab out of bounds access in squashfs_readpage_block().

This is caused by an attempt to read page index 0x2000000000.  This value
(start_index) is stored in an integer loop variable which overflows
producing a value of 0.  This causes a loop which iterates over pages
start_index -> end_index to iterate over 0 -> end_index, which ultimately
causes an out of bounds page array access.

Fix by changing variable to a loff_t, and rename to index to make it
clearer it is a page index, and not a loop count.

Link: https://lkml.kernel.org/r/20241020232200.837231-1-phillip@squashfs.org.uk
Signed-off-by: Phillip Lougher <phillip@squashfs.org.uk>
Reported-by: "Lai, Yi" <yi1.lai@linux.intel.com>
Closes: https://lore.kernel.org/all/ZwzcnCAosIPqQ9Ie@ly-workstation/
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 fs/squashfs/file_direct.c |    9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

--- a/fs/squashfs/file_direct.c~squashfs-fix-variable-overflow-in-squashfs_readpage_block
+++ a/fs/squashfs/file_direct.c
@@ -30,7 +30,8 @@ int squashfs_readpage_block(struct page
 	int mask = (1 << (msblk->block_log - PAGE_SHIFT)) - 1;
 	loff_t start_index = folio->index & ~mask;
 	loff_t end_index = start_index | mask;
-	int i, n, pages, bytes, res = -ENOMEM;
+	loff_t index;
+	int i, pages, bytes, res = -ENOMEM;
 	struct page **page, *last_page;
 	struct squashfs_page_actor *actor;
 	void *pageaddr;
@@ -45,9 +46,9 @@ int squashfs_readpage_block(struct page
 		return res;
 
 	/* Try to grab all the pages covered by the Squashfs block */
-	for (i = 0, n = start_index; n <= end_index; n++) {
-		page[i] = (n == folio->index) ? target_page :
-			grab_cache_page_nowait(target_page->mapping, n);
+	for (i = 0, index = start_index; index <= end_index; index++) {
+		page[i] = (index == folio->index) ? target_page :
+			grab_cache_page_nowait(target_page->mapping, index);
 
 		if (page[i] == NULL)
 			continue;
_

Patches currently in -mm which might be from phillip@squashfs.org.uk are

squashfs-fix-variable-overflow-in-squashfs_readpage_block.patch