linux-kernel - Re: [PATCH net-next] bpf: avoid copying junk bytes in bpf_get_current

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Date:	Wed, 09 Mar 2016 23:28:12 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	ast@...com
Cc:	daniel@...earbox.net, tobias@...dekranz.com,
	brendan.d.gregg@...il.com, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, kernel-team@...com
Subject: Re: [PATCH net-next] bpf: avoid copying junk bytes in
 bpf_get_current_comm()

From: Alexei Starovoitov <ast@...com>
Date: Wed, 9 Mar 2016 20:02:33 -0800

> Lots of places in the kernel use memcpy(buf, comm, TASK_COMM_LEN); but
> the result is typically passed to print("%s", buf) and extra bytes
> after zero don't cause any harm.
> In bpf the result of bpf_get_current_comm() is used as the part of
> map key and was causing spurious hash map mismatches.
> Use strlcpy() to guarantee zero-terminated string.
> bpf verifier checks that output buffer is zero-initialized,
> so even for short task names the output buffer don't have junk bytes.
> Note it's not a security concern, since kprobe+bpf is root only.
> 
> Fixes: ffeedafbf023 ("bpf: introduce current->pid, tgid, uid, gid, comm accessors")
> Reported-by: Tobias Waldekranz <tobias@...dekranz.com>
> Signed-off-by: Alexei Starovoitov <ast@...nel.org>
> ---
> Targeting net-next, since it's too late for net.
> I think it makes sense for stable as well.

Applied and queued up for -stable, thanks.