[PATCH] char: istallion: fix arbitrary kernel memory reads/writes

[PATCH] char: istallion: fix arbitrary kernel memory reads/writes

[Vasiliy Kulikov]

stli_brdstats is defined as global variable.  After de-BKL-ization in
the patch b4eda9cb48eac1b7 an access to the variable is not serialized
anymore.  This leads to the TOCTOU in stli_getbrdstats():

        if (copy_from_user(&stli_brdstats, bp, sizeof(combrd_t)))
                return -EFAULT;
        if (stli_brdstats.brd >= STL_MAXBRDS)  <<<<
                return -ENODEV;
        brdp = stli_brds[stli_brdstats.brd];   <<<<

If one process calls COM_GETBRDSTATS ioctl() with sane .brd, second
process calls COM_GETBRDSTATS ioctl() with invalid .brd, and the
second process' copy_from_user() executes exactly between the check and
stli_brds[] indexation of the first process, then the first process gets
contents of memory at *stli_brds[stli_brdstats.brd] address.  Also
the resulting .nrpanels field may be too big, in this case
stli_brdstats.panels array overflows.

Signed-off-by: Vasiliy Kulikov <segoon@openwall.com>
---
 drivers/char/istallion.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/drivers/char/istallion.c b/drivers/char/istallion.c
index 7c6de4c..232c5e0 100644
--- a/drivers/char/istallion.c
+++ b/drivers/char/istallion.c
@@ -186,7 +186,6 @@ static struct ktermios		stli_deftermios = {
  *	re-used for each stats call.
  */
 static comstats_t	stli_comstats;
-static combrd_t		stli_brdstats;
 static struct asystats	stli_cdkstats;
 
 /*****************************************************************************/
@@ -4005,6 +4004,7 @@ static int stli_getbrdstats(combrd_t __user *bp)
 {
 	struct stlibrd *brdp;
 	unsigned int i;
+	combrd_t stli_brdstats;
 
 	if (copy_from_user(&stli_brdstats, bp, sizeof(combrd_t)))
 		return -EFAULT;
-- 
1.7.0.4

Re: [PATCH] char: istallion: fix arbitrary kernel memory reads/writes

[Jiri Slaby]

On 04/09/2011 02:41 PM, Vasiliy Kulikov wrote:
> stli_brdstats is defined as global variable.  After de-BKL-ization in
> the patch b4eda9cb48eac1b7 an access to the variable is not serialized
> anymore.  This leads to the TOCTOU in stli_getbrdstats():

Don't use such a weird and uncommon abbreviations.

> --- a/drivers/char/istallion.c
> +++ b/drivers/char/istallion.c

Note that the code moved to staging.

regards,
-- 
js

Re: [PATCH] char: istallion: fix arbitrary kernel memory reads/writes

[Valdis.Kletnieks]

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On Sat, 09 Apr 2011 15:26:59 +0200, Jiri Slaby said:
> On 04/09/2011 02:41 PM, Vasiliy Kulikov wrote:
> > stli_brdstats is defined as global variable.  After de-BKL-ization in
> > the patch b4eda9cb48eac1b7 an access to the variable is not serialized
> > anymore.  This leads to the TOCTOU in stli_getbrdstats():
> 
> Don't use such a weird and uncommon abbreviations.

Time Of Check [to] Time Of Use.  Hardly uncommon, especially in the security
community. Googling for 'TOCTOU' and 'TOCTTOU' gets about 60K hits combined.


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Re: [PATCH] char: istallion: fix arbitrary kernel memory reads/writes

[Jiri Slaby]

On 04/09/2011 10:24 PM, Valdis.Kletnieks@vt.edu wrote:
> On Sat, 09 Apr 2011 15:26:59 +0200, Jiri Slaby said:
>> On 04/09/2011 02:41 PM, Vasiliy Kulikov wrote:
>>> stli_brdstats is defined as global variable.  After de-BKL-ization in
>>> the patch b4eda9cb48eac1b7 an access to the variable is not serialized
>>> anymore.  This leads to the TOCTOU in stli_getbrdstats():
>>
>> Don't use such a weird and uncommon abbreviations.
> 
> Time Of Check [to] Time Of Use.  Hardly uncommon, especially in the security
> community.

Well, changelogs are not for security community only. And I think I've
read far than enough papers about code analysis and never seen that before.

> Googling for 'TOCTOU' and 'TOCTTOU' gets about 60K hits combined.

Sure, I googled that a bit. But that didn't persuade me at all. It looks
like it is used by a narrow set of experts.

Whatever, I mainly wanted to point out the code move.

thanks,
-- 
js

[PATCH] char: istallion: fix arbitrary kernel memory reads/writes

[Vasiliy Kulikov]

stli_brdstats is defined as global variable.  After de-BKL-ization in
the patch b4eda9cb48eac1b7 an access to the variable is not serialized
anymore.  This leads to the race window between the check and the use
in stli_getbrdstats():

        if (copy_from_user(&stli_brdstats, bp, sizeof(combrd_t)))
                return -EFAULT;
        if (stli_brdstats.brd >= STL_MAXBRDS) <<<
                return -ENODEV;
        brdp = stli_brds[stli_brdstats.brd];  <<<

If one process calls COM_GETBRDSTATS ioctl() with sane .brd, second
process calls COM_GETBRDSTATS ioctl() with invalid .brd, and the
second process' copy_from_user() executes exactly between the check and
stli_brds[] indexation of the first process, then the first process gets
contents of memory at *stli_brds[stli_brdstats.brd] address.  Also
the resulting .nrpanels field may be too big, in this case
stli_brdstats.panels array overflows.

Signed-off-by: Vasiliy Kulikov <segoon@openwall.com>
---
 drivers/staging/tty/istallion.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/drivers/staging/tty/istallion.c b/drivers/staging/tty/istallion.c
index 0b26627..ca18cbf 100644
--- a/drivers/staging/tty/istallion.c
+++ b/drivers/staging/tty/istallion.c
@@ -186,7 +186,6 @@ static struct ktermios		stli_deftermios = {
  *	re-used for each stats call.
  */
 static comstats_t	stli_comstats;
-static combrd_t		stli_brdstats;
 static struct asystats	stli_cdkstats;
 
 /*****************************************************************************/
@@ -4005,6 +4004,7 @@ static int stli_getbrdstats(combrd_t __user *bp)
 {
 	struct stlibrd *brdp;
 	unsigned int i;
+	combrd_t stli_brdstats;
 
 	if (copy_from_user(&stli_brdstats, bp, sizeof(combrd_t)))
 		return -EFAULT;
-- 
1.7.0.4