Dear sir,
We are the ADLab, Venustech info Ltd CHINA. We have found two
vulnerabilities within linux kernel. The first one is Linux kernel IP
over ATM clip_mkip dereference freed pointer,and the second is Linux
kernel Filesystem Mount Dead Loop.Please check out the detailes about
the vulnerabilities at the end of this Email.
We are looking forward to hearing from you as soon as possible. If you
need any more information, please do not hesitate to contact us. Thank
you very much.
Best regards,
ADLab
Details:
*********************************************************
Linux kernel IP over ATM clip_mkip dereference freed pointer
[Security Advisory]
Advisory:[AD_LAB-06009] Linux kernel IP over ATM clip_mkip dereference
freed pointer
Class: Design Error
DATE:5/9/2006
CVEID:
Vulnerable:
<=Linux-2.6.*
Vendor:
http://www.kernel.org/
I.DESCRIPTION:
-------------
Linux kernel is a open source operating system.
The Linux kernel is prone to a denial-of-service vulnerability. This
issue is
due to a design error in the 'clip_mkip()' function.
II.DETAILS:
----------
There is a vulnerability in function clip_mkip(). When re-processing
received data,
a struct sk_buff pointer skb may be dereferenced after a free operation.
It will lead to a
kernel panic and denying further service.
clip_mkip (clip.c):
502 while ((skb = skb_dequeue(©)) != NULL)
503 if (!clip_devs) {
504 atm_return(vcc,skb->truesize);
505 kfree_skb(skb);
506 }
507 else {
508 unsigned int len = skb->len;
509
510 clip_push(vcc,skb);
511 PRIV(skb->dev)->stats.rx_packets--;
512 PRIV(skb->dev)->stats.rx_bytes -= len;
513 }
At line 511, PRIV(skb->dev) reference skb->dev; but after call
clip_push at line 510,
skb may be freed.
clip_push (clip.c):
198 static void clip_push(struct atm_vcc *vcc,struct sk_buff *skb)
199 {
......
234 memset(ATM_SKB(skb), 0, sizeof(struct atm_skb_data));
235 netif_rx(skb);
236 }
netif_rx (dev.c):
1392 int netif_rx(struct sk_buff *skb)
1393 {
......
1428 kfree_skb(skb); //drop skb
1429 return NET_RX_DROP;
1430 }
In netif_rx(), skb may be dropped during processing for congestion
control or by the
protocol layers; the return value NET_RX_DROP is used to identify skb
pointer arg is dropped(freed).
III.CREDIT:
----------
Venustech AD-LAB discovery this vuln.Thank to all Venustech AD-Lab guys.
V.DISCLAIMS:
-----------
The information in this bulletin is provided "AS IS" without warranty of any
kind. In no event shall we be liable for any damages whatsoever
including direct,
indirect, incidental, consequential, loss of business profits or special
damages.
Copyright 1996-2006 VENUSTECH. All Rights Reserved. Terms of use.
VENUSTECH Security Lab
VENUSTECH INFORMATION TECHNOLOGY CO.,LTD(http://www.venustech.com.cn)
Security
Trusted {Solution} Provider
Service
*********************************************************
Linux kernel Filesystem Mount Dead Loop
[Security Advisory]
Advisory: [AD_LAB-06011] Linux kernel Filesystem Mount Dead Loop
Class: Design Error
DATE:5/9/2006
CVEID:
Vulnerable:
Linux-2.6.*
Vendor:
http://www.kernel.org/
I.DESCRIPTION:
-------------
Linux kernel is an open source operating system.
The Linux kernel is prone to a denial-of-service vulnerability. This
issue is
due to a design error in the '__getblk()' function.
II.DETAILS:
----------
There is a vulnerability in function __getblk(). When mount a file
system image
with malformed block value, Linux kernel will fall in a dead loop. It
will lead to a
kernel hang and denying further service.
Function __getblk() is used to seek a corresponding buffer_head of a
block in
a specific block device. When processing a block with a block number
more than
4G and not to be mapped to buffer pages (__find_get_block will return
NULL),
__getblk_slow will always run and never return.
1478 struct buffer_head *
1479 __getblk(struct block_device *bdev, sector_t block, int size)
1480 {
1481 struct buffer_head *bh = __find_get_block(bdev, block, size);
1482
1483 might_sleep();
1484 if (bh == NULL)
1485 bh = __getblk_slow(bdev, block, size);
1486 return bh;
1487 }
The endless for loop only has a exit point (at line 1213). It terminate
only when
__find_get_block return a non-NULL value. If the block is not mapped to
buffer pages,
the first __find_get_block calling will return a NULL bh and the
function grow_buffers()
will be called subsequently.
1194 __getblk_slow(struct block_device *bdev, sector_t block, int size)
1195 {
1196 /* Size must be multiple of hard sectorsize */
1197 if (unlikely(size & (bdev_hardsect_size(bdev)-1) ||
1198 (size < 512 || size > PAGE_SIZE))) {
1199 printk(KERN_ERR "getblk(): invalid block size %d
requested\n",
1200 size);
1201 printk(KERN_ERR "hardsect size: %d\n",
1202 bdev_hardsect_size(bdev));
1203
1204 dump_stack();
1205 return NULL;
1206 }
1207
1208 for (;;) {
1209 struct buffer_head * bh;
1210
1211 bh = __find_get_block(bdev, block, size);
1212 if (bh)
1213 return bh;
1214
1215 if (!grow_buffers(bdev, block, size))
1216 free_more_memory();
1217 }
1218 }
The function grow_buffers() is responsible for construct the
relationships among
page, buffer_head and block.
On the 32-bit platform, the length of block and index are 64-bit and
32-bit respectively.
After the operations at line 1201 and 1202, the high 32 bits of block
will lost. Consequently, when
the block number is beyond 4G, new block number would be differently
with the original.
1189 static inline int
1190 grow_buffers(struct block_device *bdev, sector_t block, int size)
1191 {
1192 struct page *page;
1193 pgoff_t index;
1194 int sizebits;
1195
1196 sizebits = -1;
1197 do {
1198 sizebits++;
1199 } while ((size << sizebits) < PAGE_SIZE);
1200
1201 index = block >> sizebits;
1202 block = index << sizebits;
1203
1204 /* Create a page with the proper size buffers.. */
1205 page = grow_dev_page(bdev, block, index, size);
1206 if (!page)
1207 return 0;
1208 unlock_page(page);
1209 page_cache_release(page);
1210 return 1;
1211 }
Follow the call sequence (grow_dev_page ==> init_page_buffers ==>
init_page_buffers).
In init_page_buffers(), a new buffer_head will be initialized, it's
block number (bh->b_blocknr)
corresponding to mapped block is assigned with the new block number.
static void
init_page_buffers(struct page *page, struct block_device *bdev,
sector_t block, int size)
{
...
...
do {
if (!buffer_mapped(bh)) {
init_buffer(bh, NULL, NULL);
bh->b_bdev = bdev;
bh->b_blocknr = block;
if (uptodate)
set_buffer_uptodate(bh);
set_buffer_mapped(bh);
}
block++;
bh = bh->b_this_page;
} while (bh != head);
}
However, __find_get_block seeks buffer head base on the original block
number in __getblk_slow ().
Because of wrong block number argument, __find_get_block will always
return NULL. As results,
system will fall in a dead loop and consume resource endlessly.
1194 __getblk_slow(struct block_device *bdev, sector_t block, int size)
1195 {
...
...
1207
1208 for (;;) {
1209 struct buffer_head * bh;
1210
1211 bh = __find_get_block(bdev, block, size);
1212 if (bh)
1213 return bh;
1214
1215 if (!grow_buffers(bdev, block, size))
1216 free_more_memory();
1217 }
1218 }
example：
The vulnerability can be triggered by mount a malformed Reiser
filesystem image, the arguments of
__getblk() are:
__getblk(0xcd0ed0c0, 0xffffffffa10020d9, 0x1000)
call stack:
sys_mount ->
do_mount ->
do_kern_mount ->
get_super_block ->
get_sb_bdev ->
reiserfs_fill_super ->
reiserfs_read_locked_inode ->
search_by_key ->
__getblk ->
__find_get_block
III.CREDIT:
----------
Venustech AD-LAB discovery this vuln. Thank to all Venustech AD-Lab
guys.
V.DISCLAIMS:
-----------
The information in this bulletin is provided "AS IS" without warranty of any
kind. In no event shall we be liable for any damages whatsoever
including direct,
indirect, incidental, consequential, loss of business profits or special
damages.
Copyright 1996-2006 VENUSTECH. All Rights Reserved. Terms of use.
VENUSTECH Security Lab
VENUSTECH INFORMATION TECHNOLOGY CO.,LTD(http://www.venustech.com.cn)
Security
Trusted {Solution} Provider
Service
*********************************************************
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