On Fri, Jul 31, 2020 at 02:07:42AM +0200, Daniel Borkmann wrote:

On 7/30/20 6:13 PM, Christian Brauner wrote:

quoted

On Thu, Jul 30, 2020 at 06:09:00PM +0200, Christoph Hellwig wrote:

quoted

__bpfilter_process_sockopt never initialized the pos variable passed to
the pipe write.  This has been mostly harmless in the past as pipes
ignore the offset, but the switch to kernel_write no verified the

s/no/now/

quoted

position, which can lead to a failure depending on the exact stack
initialization patter.  Initialize the variable to zero to make

s/patter/pattern/

quoted

rw_verify_area happy.

Fixes: 6955a76fbcd5 ("bpfilter: switch to kernel_write")
Reported-by: Christian Brauner <redacted>
Reported-by: Rodrigo Madera <redacted>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Tested-by: Rodrigo Madera <redacted>
---

Thanks for tracking this down, Christoph! This fixes the logging issue
for me.
Tested-by: Christian Brauner <redacted>
Reviewed-by: Christian Brauner <redacted>

Applied to bpf & fixed up the typos in the commit msg, thanks everyone!

Daniel,
why is it necessary in bpf tree?

I fixed it already in bpf-next in commit a4fa458950b4 ("bpfilter: Initialize pos variable")
two weeks ago...