* [PATCH] dma-buf: Fix memory leak in dma_buf_set_name
@ 2019-08-16 18:00 Bharath Vedartham
2019-08-16 20:14 ` Ezequiel Garcia
0 siblings, 1 reply; 3+ messages in thread
From: Bharath Vedartham @ 2019-08-16 18:00 UTC (permalink / raw)
To: sumit.semwal
Cc: linux-media, dri-devel, linaro-mm-sig, linux-kernel, Bharath Vedartham
This patch fixes a memory leak bug reported by syzbot. Link to the
bug is given at [1].
A local variable name is used to hold the copied user buffer string
using strndup_user. strndup_user allocates memory using
kmalloc_track_caller in memdup_user. This kmalloc allocation needs to be
followed by a kfree.
This patch has been tested by a compile test.
[1] https://syzkaller.appspot.com/bug?id=ce692a3aa13e00e335e090be7846c6eb60ddff7a
Reported-by: syzbot+b2098bc44728a4efb3e9@syzkaller.appspotmail.com
Signed-off-by: Bharath Vedartham <linux.bhar@gmail.com>
---
drivers/dma-buf/dma-buf.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
index f45bfb2..9798f6d 100644
--- a/drivers/dma-buf/dma-buf.c
+++ b/drivers/dma-buf/dma-buf.c
@@ -342,6 +342,7 @@ static long dma_buf_set_name(struct dma_buf *dmabuf, const char __user *buf)
}
kfree(dmabuf->name);
dmabuf->name = name;
+ kfree(name);
out_unlock:
mutex_unlock(&dmabuf->lock);
--
2.7.4
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] dma-buf: Fix memory leak in dma_buf_set_name
2019-08-16 18:00 [PATCH] dma-buf: Fix memory leak in dma_buf_set_name Bharath Vedartham
@ 2019-08-16 20:14 ` Ezequiel Garcia
2019-08-18 18:05 ` Bharath Vedartham
0 siblings, 1 reply; 3+ messages in thread
From: Ezequiel Garcia @ 2019-08-16 20:14 UTC (permalink / raw)
To: Bharath Vedartham, sumit.semwal
Cc: linux-media, dri-devel, linaro-mm-sig, linux-kernel
Hi Bharath,
Thanks for taking the time to try to fix this report.
However, this doesn't look right.
On Fri, 2019-08-16 at 23:30 +0530, Bharath Vedartham wrote:
> This patch fixes a memory leak bug reported by syzbot. Link to the
> bug is given at [1].
>
> A local variable name is used to hold the copied user buffer string
> using strndup_user. strndup_user allocates memory using
> kmalloc_track_caller in memdup_user. This kmalloc allocation needs to be
> followed by a kfree.
>
> This patch has been tested by a compile test.
>
> [1] https://syzkaller.appspot.com/bug?id=ce692a3aa13e00e335e090be7846c6eb60ddff7a
>
> Reported-by: syzbot+b2098bc44728a4efb3e9@syzkaller.appspotmail.com
> Signed-off-by: Bharath Vedartham <linux.bhar@gmail.com>
> ---
> drivers/dma-buf/dma-buf.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
> index f45bfb2..9798f6d 100644
> --- a/drivers/dma-buf/dma-buf.c
> +++ b/drivers/dma-buf/dma-buf.c
> @@ -342,6 +342,7 @@ static long dma_buf_set_name(struct dma_buf *dmabuf, const char __user *buf)
> }
> kfree(dmabuf->name);
> dmabuf->name = name;
> + kfree(name);
>
Just by looking at this, you can deduce something is not right.
You are assigning "name" to dmabuf->name, but then releasing "name"!
So now, dmabuf->name has free memory, which will lead to
user-after-free issues.
Note also, that this function doesn't look leaky since the previous
"name" is freed, before setting a new one.
Maybe the syzbot report is some kind of false positive?
Also, I _strongly_ suggest that in the future you don't compile-test
only these kind of not trivial fixes. Since you are touching a crucial
part of the kernel here, you should really be testing properly.
Specially since syzbot produces a reproducer.
Consider compile test as something you do when your changes are
only cosmetic, and you are completely and absolutely sure things
will be OK.
Thanks.
Ezequiel
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] dma-buf: Fix memory leak in dma_buf_set_name
2019-08-16 20:14 ` Ezequiel Garcia
@ 2019-08-18 18:05 ` Bharath Vedartham
0 siblings, 0 replies; 3+ messages in thread
From: Bharath Vedartham @ 2019-08-18 18:05 UTC (permalink / raw)
To: Ezequiel Garcia
Cc: sumit.semwal, linux-media, dri-devel, linaro-mm-sig, linux-kernel
On Fri, Aug 16, 2019 at 05:14:24PM -0300, Ezequiel Garcia wrote:
> Hi Bharath,
>
> Thanks for taking the time to try to fix this report.
>
> However, this doesn't look right.
>
> On Fri, 2019-08-16 at 23:30 +0530, Bharath Vedartham wrote:
> > This patch fixes a memory leak bug reported by syzbot. Link to the
> > bug is given at [1].
> >
> > A local variable name is used to hold the copied user buffer string
> > using strndup_user. strndup_user allocates memory using
> > kmalloc_track_caller in memdup_user. This kmalloc allocation needs to be
> > followed by a kfree.
> >
> > This patch has been tested by a compile test.
> >
> > [1] https://syzkaller.appspot.com/bug?id=ce692a3aa13e00e335e090be7846c6eb60ddff7a
> >
> > Reported-by: syzbot+b2098bc44728a4efb3e9@syzkaller.appspotmail.com
> > Signed-off-by: Bharath Vedartham <linux.bhar@gmail.com>
> > ---
> > drivers/dma-buf/dma-buf.c | 1 +
> > 1 file changed, 1 insertion(+)
> >
> > diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
> > index f45bfb2..9798f6d 100644
> > --- a/drivers/dma-buf/dma-buf.c
> > +++ b/drivers/dma-buf/dma-buf.c
> > @@ -342,6 +342,7 @@ static long dma_buf_set_name(struct dma_buf *dmabuf, const char __user *buf)
> > }
> > kfree(dmabuf->name);
> > dmabuf->name = name;
> > + kfree(name);
> >
>
> Just by looking at this, you can deduce something is not right.
> You are assigning "name" to dmabuf->name, but then releasing "name"!
>
> So now, dmabuf->name has free memory, which will lead to
> user-after-free issues.
>
> Note also, that this function doesn't look leaky since the previous
> "name" is freed, before setting a new one.
>
> Maybe the syzbot report is some kind of false positive?
>
> Also, I _strongly_ suggest that in the future you don't compile-test
> only these kind of not trivial fixes. Since you are touching a crucial
> part of the kernel here, you should really be testing properly.
>
> Specially since syzbot produces a reproducer.
>
> Consider compile test as something you do when your changes are
> only cosmetic, and you are completely and absolutely sure things
> will be OK.
>
> Thanks.
> Ezequiel
Hi Ezequiel,
Thank you for taking the time to review this.
I made a mistake here and thank you for notifying me of it.
Thank you for your comments, I ll keep them in mind before sending
patches to the kernel :)
Thank you
Bharath
^ permalink raw reply [flat|nested] 3+ messages in thread
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2019-08-16 18:00 [PATCH] dma-buf: Fix memory leak in dma_buf_set_name Bharath Vedartham
2019-08-16 20:14 ` Ezequiel Garcia
2019-08-18 18:05 ` Bharath Vedartham
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