* stm class: Prevent user-controllable allocations
@ 2019-05-07 12:41 Pavel Machek
2019-05-07 12:50 ` Dan Carpenter
0 siblings, 1 reply; 3+ messages in thread
From: Pavel Machek @ 2019-05-07 12:41 UTC (permalink / raw)
To: alexander.shishkin, security, sasha.levin, gregkh, kernel list,
Andrew Morton, trivial
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It seems to me that we still allow overflow if count == ~0. We'll then
allocate 0 bytes but copy ~0 bytes. That does not sound healthy.
Fixes: f08b18266c7116e2ec6885dd53a928f580060a71
Signed-off-by: Pavel Machek <pavel@denx.de>
diff --git a/drivers/hwtracing/stm/core.c b/drivers/hwtracing/stm/core.c
index c7ba8ac..8846fca 100644
--- a/drivers/hwtracing/stm/core.c
+++ b/drivers/hwtracing/stm/core.c
@@ -631,7 +631,7 @@ static ssize_t stm_char_write(struct file *file, const char __user *buf,
char *kbuf;
int err;
- if (count + 1 > PAGE_SIZE)
+ if (count > PAGE_SIZE - 1)
count = PAGE_SIZE - 1;
/*
--
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: stm class: Prevent user-controllable allocations
2019-05-07 12:41 stm class: Prevent user-controllable allocations Pavel Machek
@ 2019-05-07 12:50 ` Dan Carpenter
2019-05-07 15:11 ` Pavel Machek
0 siblings, 1 reply; 3+ messages in thread
From: Dan Carpenter @ 2019-05-07 12:50 UTC (permalink / raw)
To: Pavel Machek
Cc: alexander.shishkin, security, sasha.levin, gregkh, kernel list,
Andrew Morton, trivial
On Tue, May 07, 2019 at 02:41:13PM +0200, Pavel Machek wrote:
>
> It seems to me that we still allow overflow if count == ~0. We'll then
> allocate 0 bytes but copy ~0 bytes. That does not sound healthy.
>
> Fixes: f08b18266c7116e2ec6885dd53a928f580060a71
>
> Signed-off-by: Pavel Machek <pavel@denx.de>
>
> diff --git a/drivers/hwtracing/stm/core.c b/drivers/hwtracing/stm/core.c
> index c7ba8ac..8846fca 100644
> --- a/drivers/hwtracing/stm/core.c
> +++ b/drivers/hwtracing/stm/core.c
> @@ -631,7 +631,7 @@ static ssize_t stm_char_write(struct file *file, const char __user *buf,
> char *kbuf;
> int err;
>
> - if (count + 1 > PAGE_SIZE)
> + if (count > PAGE_SIZE - 1)
> count = PAGE_SIZE - 1;
The "count" variable should all be checked in vfs_write(). count + off
is checked in rw_verify_area() and count is capped at MAX_RW_COUNT.
#define MAX_RW_COUNT (INT_MAX & PAGE_MASK)
regards,
dan carpenter
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: stm class: Prevent user-controllable allocations
2019-05-07 12:50 ` Dan Carpenter
@ 2019-05-07 15:11 ` Pavel Machek
0 siblings, 0 replies; 3+ messages in thread
From: Pavel Machek @ 2019-05-07 15:11 UTC (permalink / raw)
To: Dan Carpenter
Cc: Pavel Machek, alexander.shishkin, security, sasha.levin, gregkh,
kernel list, Andrew Morton, trivial
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On Tue 2019-05-07 15:50:27, Dan Carpenter wrote:
> On Tue, May 07, 2019 at 02:41:13PM +0200, Pavel Machek wrote:
> >
> > It seems to me that we still allow overflow if count == ~0. We'll then
> > allocate 0 bytes but copy ~0 bytes. That does not sound healthy.
> >
> > Fixes: f08b18266c7116e2ec6885dd53a928f580060a71
> >
> > Signed-off-by: Pavel Machek <pavel@denx.de>
> >
> > diff --git a/drivers/hwtracing/stm/core.c b/drivers/hwtracing/stm/core.c
> > index c7ba8ac..8846fca 100644
> > --- a/drivers/hwtracing/stm/core.c
> > +++ b/drivers/hwtracing/stm/core.c
> > @@ -631,7 +631,7 @@ static ssize_t stm_char_write(struct file *file, const char __user *buf,
> > char *kbuf;
> > int err;
> >
> > - if (count + 1 > PAGE_SIZE)
> > + if (count > PAGE_SIZE - 1)
> > count = PAGE_SIZE - 1;
>
> The "count" variable should all be checked in vfs_write(). count + off
> is checked in rw_verify_area() and count is capped at MAX_RW_COUNT.
>
> #define MAX_RW_COUNT (INT_MAX & PAGE_MASK)
Ok, so overflow is checked elsewhere. I'd still like patch to be
applied as it makes code more obvious.
Thanks,
Pavel
--
DENX Software Engineering GmbH, Managing Director: Wolfgang Denk
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
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2019-05-07 12:41 stm class: Prevent user-controllable allocations Pavel Machek
2019-05-07 12:50 ` Dan Carpenter
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