A Sysbot [1] corrupted filesystem exposes two flaws in the handling and
sanity checking of the xattr_ids count in the filesystem. Both of these
flaws cause computation overflow due to incorrect typing.
In the corrupted filesystem the xattr_ids value is 4294967071, which
stored in a signed variable becomes the negative number -225.
Flaw 1 (64-bit systems only):
The signed integer xattr_ids variable causes sign extension.
This causes variable overflow in the SQUASHFS_XATTR_*(A) macros. The
variable is first multiplied by sizeof(struct squashfs_xattr_id) where the
type of the sizeof operator is "unsigned long".
On a 64-bit system this is 64-bits in size, and causes the negative number
to be sign extended and widened to 64-bits and then become unsigned. This
produces the very large number 18446744073709548016 or 2^64 - 3600. This
number when rounded up by SQUASHFS_METADATA_SIZE - 1 (8191 bytes) and
divided by SQUASHFS_METADATA_SIZE overflows and produces a length of 0
(stored in len).
Flaw 2 (32-bit systems only):
On a 32-bit system the integer variable is not widened by the unsigned
long type of the sizeof operator (32-bits), and the signedness of the
variable has no effect due it always being treated as unsigned.
The above corrupted xattr_ids value of 4294967071, when multiplied
overflows and produces the number 4294963696 or 2^32 - 3400. This number
when rounded up by SQUASHFS_METADATA_SIZE - 1 (8191 bytes) and divided by
SQUASHFS_METADATA_SIZE overflows again and produces a length of 0.
The effect of the 0 length computation:
In conjunction with the corrupted xattr_ids field, the filesystem also has
a corrupted xattr_table_start value, where it matches the end of
filesystem value of 850.
This causes the following sanity check code to fail because the
incorrectly computed len of 0 matches the incorrect size of the table
reported by the superblock (0 bytes).
len = SQUASHFS_XATTR_BLOCK_BYTES(*xattr_ids);
indexes = SQUASHFS_XATTR_BLOCKS(*xattr_ids);
/*
* The computed size of the index table (len bytes) should exactly
* match the table start and end points
*/
start = table_start + sizeof(*id_table);
end = msblk->bytes_used;
if (len != (end - start))
return ERR_PTR(-EINVAL);
Changing the xattr_ids variable to be "usigned int" fixes the flaw on a
64-bit system. This relies on the fact the computation is widened by the
unsigned long type of the sizeof operator.
Casting the variable to u64 in the above macro fixes this flaw on a 32-bit
system.
It also means 64-bit systems do not implicitly rely on the type of the
sizeof operator to widen the computation.
[1] https://lore.kernel.org/lkml/000000000000cd44f005f1a0f17f@google.com/
Link: https://lkml.kernel.org/r/20230127061842.10965-1-phillip@squashfs.org.uk
Fixes: 506220d2ba ("squashfs: add more sanity checks in xattr id lookup")
Signed-off-by: Phillip Lougher <phillip@squashfs.org.uk>
Reported-by: <syzbot+082fa4af80a5bb1a9843@syzkaller.appspotmail.com>
Cc: Alexey Khoroshilov <khoroshilov@ispras.ru>
Cc: Fedor Pchelkin <pchelkin@ispras.ru>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Sysbot has reported a number of "slab-out-of-bounds reads" and
"use-after-free read" errors which has been identified as being caused
by a corrupted index value read from the inode. This could be because
the metadata block is uncompressed, or because the "compression" bit has
been corrupted (turning a compressed block into an uncompressed block).
This patch adds additional sanity checks to detect this, and the
following corruption.
1. It checks against corruption of the ids count. This can either
lead to a larger table to be read, or a smaller than expected
table to be read.
In the case of a too large ids count, this would often have been
trapped by the existing sanity checks, but this patch introduces
a more exact check, which can identify too small values.
2. It checks the contents of the index table for corruption.
Link: https://lkml.kernel.org/r/20210204130249.4495-3-phillip@squashfs.org.uk
Signed-off-by: Phillip Lougher <phillip@squashfs.org.uk>
Reported-by: syzbot+b06d57ba83f604522af2@syzkaller.appspotmail.com
Reported-by: syzbot+c021ba012da41ee9807c@syzkaller.appspotmail.com
Reported-by: syzbot+5024636e8b5fd19f0f19@syzkaller.appspotmail.com
Reported-by: syzbot+bcbc661df46657d0fa4f@syzkaller.appspotmail.com
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Based on 1 normalized pattern(s):
this program is free software you can redistribute it and or modify
it under the terms of the gnu general public license as published by
the free software foundation either version 2 or at your option any
later version this program is distributed in the hope that it will
be useful but without any warranty without even the implied warranty
of merchantability or fitness for a particular purpose see the gnu
general public license for more details you should have received a
copy of the gnu general public license along with this program if
not write to the free software foundation 51 franklin street fifth
floor boston ma 02110 1301 usa
extracted by the scancode license scanner the SPDX license identifier
GPL-2.0-or-later
has been chosen to replace the boilerplate/reference in 23 file(s).
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Allison Randal <allison@lohutok.net>
Reviewed-by: Kate Stewart <kstewart@linuxfoundation.org>
Cc: linux-spdx@vger.kernel.org
Link: https://lkml.kernel.org/r/20190520170857.458548087@linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
These inode operations are no longer used; remove them.
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
My existing email address may stop working in a month or two, so update
email to one that will continue working.
Signed-off-by: Phillip Lougher <phillip@lougher.demon.co.uk>
Fsfuzzer generates corrupted filesystems which throw a warn_on in
kmalloc. One of these is due to a corrupted superblock no_ids field.
Fix this by checking that the number of bytes to be read (and allocated)
does not extend into the next filesystem structure.
Also add a couple of other sanity checks of the mount-time id table
structures.
Signed-off-by: Phillip Lougher <phillip@lougher.demon.co.uk>
The fourth argument should be unsigned. Also add missing include
so that the function prototype is defined in xattr_id.c
This fixes a couple of sparse warnings.
Signed-off-by: Phillip Lougher <phillip@lougher.demon.co.uk>
Sparse detected that unsigned pointer was being passed as int pointer.
Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
[fixed up to deal with code refactoring]
Signed-off-by: Phillip Lougher <phillip@lougher.demon.co.uk>
Phillip Lougher