From: Greg KH <gregkh@suse.de>
To: linux-kernel@vger.kernel.org, stable@vger.kernel.org
Cc: torvalds@linux-foundation.org, akpm@linux-foundation.org,
alan@lxorguk.ukuu.org.uk, Xi Wang <xi.wang@gmail.com>,
"Theodore Tso" <tytso@mit.edu>
Subject: [01/27] ext4: fix undefined behavior in ext4_fill_flex_info()
Date: Mon, 23 Jan 2012 15:40:47 -0800 [thread overview]
Message-ID: <20120123234201.776571387@clark.kroah.org> (raw)
In-Reply-To: <20120123234224.GA19510@kroah.com>
2.6.32-longterm review patch. If anyone has any objections, please let me know.
------------------
From: Xi Wang <xi.wang@gmail.com>
commit d50f2ab6f050311dbf7b8f5501b25f0bf64a439b upstream.
Commit 503358ae01b70ce6909d19dd01287093f6b6271c ("ext4: avoid divide by
zero when trying to mount a corrupted file system") fixes CVE-2009-4307
by performing a sanity check on s_log_groups_per_flex, since it can be
set to a bogus value by an attacker.
sbi->s_log_groups_per_flex = sbi->s_es->s_log_groups_per_flex;
groups_per_flex = 1 << sbi->s_log_groups_per_flex;
if (groups_per_flex < 2) { ... }
This patch fixes two potential issues in the previous commit.
1) The sanity check might only work on architectures like PowerPC.
On x86, 5 bits are used for the shifting amount. That means, given a
large s_log_groups_per_flex value like 36, groups_per_flex = 1 << 36
is essentially 1 << 4 = 16, rather than 0. This will bypass the check,
leaving s_log_groups_per_flex and groups_per_flex inconsistent.
2) The sanity check relies on undefined behavior, i.e., oversized shift.
A standard-confirming C compiler could rewrite the check in unexpected
ways. Consider the following equivalent form, assuming groups_per_flex
is unsigned for simplicity.
groups_per_flex = 1 << sbi->s_log_groups_per_flex;
if (groups_per_flex == 0 || groups_per_flex == 1) {
We compile the code snippet using Clang 3.0 and GCC 4.6. Clang will
completely optimize away the check groups_per_flex == 0, leaving the
patched code as vulnerable as the original. GCC keeps the check, but
there is no guarantee that future versions will do the same.
Signed-off-by: Xi Wang <xi.wang@gmail.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
---
fs/ext4/super.c | 7 +++----
1 file changed, 3 insertions(+), 4 deletions(-)
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -1705,17 +1705,16 @@ static int ext4_fill_flex_info(struct su
struct ext4_group_desc *gdp = NULL;
ext4_group_t flex_group_count;
ext4_group_t flex_group;
- int groups_per_flex = 0;
+ unsigned int groups_per_flex = 0;
size_t size;
int i;
sbi->s_log_groups_per_flex = sbi->s_es->s_log_groups_per_flex;
- groups_per_flex = 1 << sbi->s_log_groups_per_flex;
-
- if (groups_per_flex < 2) {
+ if (sbi->s_log_groups_per_flex < 1 || sbi->s_log_groups_per_flex > 31) {
sbi->s_log_groups_per_flex = 0;
return 1;
}
+ groups_per_flex = 1 << sbi->s_log_groups_per_flex;
/* We allocate both existing and potentially added groups */
flex_group_count = ((sbi->s_groups_count + groups_per_flex - 1) +
next prev parent reply other threads:[~2012-01-23 23:40 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-01-23 23:42 [00/27] 2.6.32.55-longterm review Greg KH
2012-01-23 23:40 ` Greg KH [this message]
2012-01-23 23:40 ` [02/27] ALSA: snd-usb-us122l: Delete calls to preempt_disable Greg KH
2012-01-23 23:40 ` [03/27] ALSA: ice1724 - Check for ac97 to avoid kernel oops Greg KH
2012-01-23 23:40 ` [04/27] ALSA: hda - Return the error from get_wcaps_type() for invalid NIDs Greg KH
2012-01-23 23:40 ` [05/27] HID: bump maximum global item tag report size to 96 bytes Greg KH
2012-01-23 23:40 ` [06/27] UBI: fix use-after-free on error path Greg KH
2012-01-23 23:40 ` [07/27] PCI: Fix PCI_EXP_TYPE_RC_EC value Greg KH
2012-01-23 23:40 ` [08/27] PCI: msi: Disable msi interrupts when we initialize a pci device Greg KH
2012-01-23 23:40 ` [09/27] xen/xenbus: Reject replies with payload > XENSTORE_PAYLOAD_MAX Greg KH
2012-01-23 23:40 ` [10/27] ima: free duplicate measurement memory Greg KH
2012-01-23 23:40 ` [11/27] PNP: work around Dell 1536/1546 BIOS MMCONFIG bug that breaks USB Greg KH
2012-01-23 23:40 ` [12/27] x86: Fix mmap random address range Greg KH
2012-01-23 23:40 ` [13/27] UBI: fix nameless volumes handling Greg KH
2012-01-23 23:41 ` [14/27] i2c: Fix error value returned by several bus drivers Greg KH
2012-01-23 23:41 ` [15/27] [media] V4L/DVB: v4l2-ioctl: integer overflow in video_usercopy() Greg KH
2012-01-23 23:41 ` [16/27] svcrpc: fix double-free on shutdown of nfsd after changing pool mode Greg KH
2012-01-23 23:41 ` [17/27] svcrpc: destroy server sockets all at once Greg KH
2012-01-23 23:41 ` [18/27] nfsd: Fix oops when parsing a 0 length export Greg KH
2012-01-23 23:41 ` [19/27] USB: cdc-wdm: fix misuse of logical operation in place of bitop Greg KH
2012-01-23 23:41 ` [20/27] [S390] fix cputime overflow in uptime_proc_show Greg KH
2012-01-23 23:41 ` [21/27] USB: Fix bad dma problem on WDM device disconnect Greg KH
2012-01-23 23:41 ` [22/27] block: add and use scsi_blk_cmd_ioctl Greg KH
2012-01-23 23:41 ` [23/27] kernel.h: add printk_ratelimited and pr_<level>_rl Greg KH
2012-01-24 14:46 ` Phil Carmody
2012-01-24 16:35 ` Ben Hutchings
2012-01-24 16:43 ` Greg KH
2012-01-23 23:41 ` [24/27] ALSA: HDA: Fix internal microphone on Dell Studio 16 XPS 1645 Greg KH
2012-01-23 23:41 ` [25/27] [SCSI] sym53c8xx: Fix NULL pointer dereference in slave_destroy Greg KH
2012-01-23 23:41 ` [26/27] score: fix off-by-one index into syscall table Greg KH
2012-01-23 23:41 ` [27/27] kprobes: initialize before using a hlist Greg KH
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20120123234201.776571387@clark.kroah.org \
--to=gregkh@suse.de \
--cc=akpm@linux-foundation.org \
--cc=alan@lxorguk.ukuu.org.uk \
--cc=linux-kernel@vger.kernel.org \
--cc=stable@vger.kernel.org \
--cc=torvalds@linux-foundation.org \
--cc=tytso@mit.edu \
--cc=xi.wang@gmail.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.