Commit cdc4e47d authored Mar 09, 2016 by Alexei Starovoitov Committed by David S. Miller Mar 09, 2016

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: ffeedafb ("bpf: introduce current->pid, tgid, uid, gid, comm accessors")
Reported-by: Tobias Waldekranz <tobias@waldekranz.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent b8cdc051

kernel/bpf/helpers.c

+1 −1

Original line number	Original line	Diff line number	Diff line
	@@ -166,7 +166,7 @@ static u64 bpf_get_current_comm(u64 r1, u64 size, u64 r3, u64 r4, u64 r5)
	if (!task)		if (!task)
	return -EINVAL;		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;		return 0;
	}		}