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Squashfs: fix variable overflow in squashfs_readpage_block

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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>
This commit is contained in:
Phillip Lougher 2024-10-21 00:22:00 +01:00 committed by Andrew Morton
parent 330d8df81f
commit d31638ff6c
1 changed files with 5 additions and 4 deletions
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9
fs/squashfs/file_direct.c
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@ -30,7 +30,8 @@ int squashfs_readpage_block(struct page *target_page, u64 block, int bsize,
int mask = (1 << (msblk->block_log - PAGE_SHIFT)) - 1; int mask = (1 << (msblk->block_log - PAGE_SHIFT)) - 1;
loff_t start_index = folio->index & ~mask; loff_t start_index = folio->index & ~mask;
loff_t end_index = start_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 page **page, *last_page;
struct squashfs_page_actor *actor; struct squashfs_page_actor *actor;
void *pageaddr; void *pageaddr;
@ -45,9 +46,9 @@ int squashfs_readpage_block(struct page *target_page, u64 block, int bsize,
return res; return res;
/* Try to grab all the pages covered by the Squashfs block */ /* Try to grab all the pages covered by the Squashfs block */
for (i = 0, n = start_index; n <= end_index; n++) { for (i = 0, index = start_index; index <= end_index; index++) {
page[i] = (n == folio->index) ? target_page : page[i] = (index == folio->index) ? target_page :
grab_cache_page_nowait(target_page->mapping, n); grab_cache_page_nowait(target_page->mapping, index);
if (page[i] == NULL) if (page[i] == NULL)
continue; continue;