bpf: Fix a buffer out-of-bound access when filling raw_tp link_info

Commit f2e10bff16a0 ("bpf: Add support for BPF_OBJ_GET_INFO_BY_FD for bpf_link")
added link query for raw_tp. One of fields in link_info is to
fill a user buffer with tp_name. The Scurrent checking only
declares "ulen && !ubuf" as invalid. So "!ulen && ubuf" will be
valid. Later on, we do "copy_to_user(ubuf, tp_name, ulen - 1)" which
may overwrite user memory incorrectly.

This patch fixed the problem by disallowing "!ulen && ubuf" case as well.

Fixes: f2e10bff16a0 ("bpf: Add support for BPF_OBJ_GET_INFO_BY_FD for bpf_link")
Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/20200821191054.714731-1-yhs@fb.com

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 86299a2..ac6c784 100644 (file)
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -2634,7 +2634,7 @@ static int bpf_raw_tp_link_fill_link_info(const struct bpf_link *link,
        u32 ulen = info->raw_tracepoint.tp_name_len;
        size_t tp_len = strlen(tp_name);
 
-       if (ulen && !ubuf)
+       if (!ulen ^ !ubuf)
                return -EINVAL;
 
        info->raw_tracepoint.tp_name_len = tp_len + 1;