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Date: Wed, 9 Mar 2016 20:02:33 -0800 From: Alexei Starovoitov <ast@...com> To: "David S . Miller" <davem@...emloft.net> CC: Daniel Borkmann <daniel@...earbox.net>, Tobias Waldekranz <tobias@...dekranz.com>, Brendan Gregg <brendan.d.gregg@...il.com>, <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>, <kernel-team@...com> Subject: [PATCH net-next] bpf: avoid copying junk bytes in bpf_get_current_comm() 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. kernel/bpf/helpers.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c index 4504ca66118d..50da680c479f 100644 --- a/kernel/bpf/helpers.c +++ b/kernel/bpf/helpers.c @@ -166,7 +166,7 @@ static u64 bpf_get_current_comm(u64 r1, u64 size, u64 r3, u64 r4, u64 r5) if (!task) return -EINVAL; - memcpy(buf, task->comm, min_t(size_t, size, sizeof(task->comm))); + strlcpy(buf, task->comm, min_t(size_t, size, sizeof(task->comm))); return 0; } -- 2.8.0.rc1
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