From: Alexei Starovoitov Date: Thu, 10 Mar 2016 04:02:33 +0000 (-0800) Subject: bpf: avoid copying junk bytes in bpf_get_current_comm() X-Git-Url: http://git.osdn.net/view?a=commitdiff_plain;h=e8e43232627082328fa4016fab1960360360f167;p=sagit-ice-cold%2Fkernel_xiaomi_msm8998.git bpf: avoid copying junk bytes in bpf_get_current_comm() [ Upstream commit cdc4e47da8f4c32eeb6b2061a8a834f4362a12b7 ] 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 Signed-off-by: Alexei Starovoitov Signed-off-by: David S. Miller Signed-off-by: Greg Kroah-Hartman --- 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; }