[PATCH] fs/squashfs: restrict length of xattr_ids in read_xattr_id_table

From: Sabyrzhan Tasbolatov <snovitoll@gmail.com>
To: phillip@squashfs.org.uk
Cc: linux-kernel@vger.kernel.org,
	syzbot+2ccea6339d368360800d@syzkaller.appspotmail.com
Subject: [PATCH] fs/squashfs: restrict length of xattr_ids in read_xattr_id_table
Date: Wed,  3 Feb 2021 16:35:13 +0600	[thread overview]
Message-ID: <20210203103513.1510005-1-snovitoll@gmail.com> (raw)

syzbot found WARNING in squashfs_read_table [1] when length of xattr_ids
exceeds KMALLOC_MAX_SIZE in squashfs_read_table() for kmalloc().

For other squashfs tables, currently such as boundary is checked with
another table's boundaries. Xattr table is the last one, so there is
no defined limit. But to avoid order >= MAX_ORDER warning condition,
we should restrict SQUASHFS_XATTR_BLOCK_BYTES(*xattr_ids) to
KMALLOC_MAX_SIZE, and it gives 1024 pages in squashfs_read_table via
(length + PAGE_SIZE - 1) >> PAGE_SHIFT.

[1]
Call Trace:
 alloc_pages_current+0x18c/0x2a0 mm/mempolicy.c:2267
 alloc_pages include/linux/gfp.h:547 [inline]
 kmalloc_order+0x2e/0xb0 mm/slab_common.c:916
 kmalloc_order_trace+0x14/0x120 mm/slab_common.c:932
 kmalloc include/linux/slab.h:559 [inline]
 squashfs_read_table+0x43/0x1e0 fs/squashfs/cache.c:413
 squashfs_read_xattr_id_table+0x191/0x220 fs/squashfs/xattr_id.c:81

Reported-by: syzbot+2ccea6339d368360800d@syzkaller.appspotmail.com
Signed-off-by: Sabyrzhan Tasbolatov <snovitoll@gmail.com>
---
 fs/squashfs/xattr_id.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/squashfs/xattr_id.c b/fs/squashfs/xattr_id.c
index d99e08464554..6bb51cd3d5c1 100644
--- a/fs/squashfs/xattr_id.c
+++ b/fs/squashfs/xattr_id.c
@@ -78,5 +78,8 @@ __le64 *squashfs_read_xattr_id_table(struct super_block *sb, u64 start,
 
 	TRACE("In read_xattr_index_table, length %d\n", len);
 
+	if (len > KMALLOC_MAX_SIZE)
+		return -ENOMEM;
+
 	return squashfs_read_table(sb, start + sizeof(*id_table), len);
 }
-- 
2.25.1

