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=ce692a3aa13e00e335e090be7846c6eb60ddff7...
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