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Date: Tue, 27 Feb 2024 10:49:42 +0000
From: Donald Hunter <donald.hunter@...il.com>
To: Jakub Kicinski <kuba@...nel.org>
Cc: davem@...emloft.net, netdev@...r.kernel.org, edumazet@...gle.com,
pabeni@...hat.com, jiri@...nulli.us, sdf@...gle.com,
nicolas.dichtel@...nd.com
Subject: Re: [PATCH net-next 00/15] tools: ynl: stop using libmnl
Jakub Kicinski <kuba@...nel.org> writes:
> On Mon, 26 Feb 2024 09:04:12 +0000 Donald Hunter wrote:
>> > On Fri, 23 Feb 2024 16:26:33 +0000 Donald Hunter wrote:
>> >> Is the absence of buffer bounds checking intentional, i.e. relying on libasan?
>> >
>> > In ynl.c or the generated code?
>>
>> I'm looking at ynl_attr_nest_start() and ynl_attr_put*() in ynl-priv.h
>> and there's no checks for buffer overrun. It is admittedly a big
>> buffer, with rx following tx, but still.
>
> You're right. But this series isn't making it worse, AFAIU.
> We weren't checking before, we aren't checking now.
Agreed, libmnl had the same issue.
> I don't want to have to add another arg to all put() calls.
> How about we sash the max len on nlmsg_pid?
Seems reasonable. Minor comments below.
> Something like:
>
> diff --git a/tools/net/ynl/lib/ynl-priv.h b/tools/net/ynl/lib/ynl-priv.h
> index 6361318e5c4c..d4ffe18b00f9 100644
> --- a/tools/net/ynl/lib/ynl-priv.h
> +++ b/tools/net/ynl/lib/ynl-priv.h
> @@ -135,6 +135,8 @@ int ynl_error_parse(struct ynl_parse_arg *yarg, const char *msg);
>
> /* Netlink message handling helpers */
>
> +#define YNL_MSG_OVERFLOW 1
> +
> static inline struct nlmsghdr *ynl_nlmsg_put_header(void *buf)
> {
> struct nlmsghdr *nlh = buf;
> @@ -239,11 +241,26 @@ ynl_attr_first(const void *start, size_t len, size_t skip)
> return ynl_attr_if_good(start + len, attr);
> }
>
> +static inline bool
> +__ynl_attr_put_overflow(struct nlmsghdr *nlh, size_t size)
> +{
> + bool o;
> +
> + /* We stash buffer length on nlmsg_pid. */
> + o = nlh->nlmsg_len + NLA_HDRLEN + NLMSG_ALIGN(size) > nlh->nlmsg_pid;
The comment confused me here. How about "We compare against stashed buffer
length in nlmsg_pid".
> + if (o)
> + nlh->nlmsg_pid = YNL_MSG_OVERFLOW;
It took me a moment to realise that this behaves like a very short
buffer length for subsequent calls to __ynl_attr_put_overflow(). Is it
worth extending the comment in ynl_msg_start() to say "buffer length or
overflow status"?
> + return o;
> +}
> +
> static inline struct nlattr *
> ynl_attr_nest_start(struct nlmsghdr *nlh, unsigned int attr_type)
> {
> struct nlattr *attr;
>
> + if (__ynl_attr_put_overflow(nlh, 0))
> + return ynl_nlmsg_end_addr(nlh) - NLA_HDRLEN;
Is the idea here to return a struct nlattr * that is safe to use?
Shouldn't we zero the values in the buffer first?
> +
> attr = ynl_nlmsg_end_addr(nlh);
> attr->nla_type = attr_type | NLA_F_NESTED;
> nlh->nlmsg_len += NLMSG_ALIGN(sizeof(struct nlattr));
> @@ -263,6 +280,9 @@ ynl_attr_put(struct nlmsghdr *nlh, unsigned int attr_type,
> {
> struct nlattr *attr;
>
> + if (__ynl_attr_put_overflow(nlh, size))
> + return;
> +
> attr = ynl_nlmsg_end_addr(nlh);
> attr->nla_type = attr_type;
> attr->nla_len = NLA_HDRLEN + size;
> @@ -276,14 +296,17 @@ static inline void
> ynl_attr_put_str(struct nlmsghdr *nlh, unsigned int attr_type, const char *str)
> {
> struct nlattr *attr;
> - const char *end;
> + size_t len;
> +
> + len = strlen(str);
> + if (__ynl_attr_put_overflow(nlh, len))
> + return;
>
> attr = ynl_nlmsg_end_addr(nlh);
> attr->nla_type = attr_type;
>
> - end = stpcpy(ynl_attr_data(attr), str);
> - attr->nla_len =
> - NLA_HDRLEN + NLA_ALIGN(end - (char *)ynl_attr_data(attr));
> + strcpy(ynl_attr_data(attr), str);
> + attr->nla_len = NLA_HDRLEN + NLA_ALIGN(len);
>
> nlh->nlmsg_len += NLMSG_ALIGN(attr->nla_len);
> }
> diff --git a/tools/net/ynl/lib/ynl.c b/tools/net/ynl/lib/ynl.c
> index 86729119e1ef..c2ba72f68028 100644
> --- a/tools/net/ynl/lib/ynl.c
> +++ b/tools/net/ynl/lib/ynl.c
> @@ -404,9 +404,33 @@ struct nlmsghdr *ynl_msg_start(struct ynl_sock *ys, __u32 id, __u16 flags)
> nlh->nlmsg_flags = flags;
> nlh->nlmsg_seq = ++ys->seq;
>
> + /* This is a local YNL hack for length checking, we put the buffer
> + * length in nlmsg_pid, since messages sent to the kernel always use
> + * PID 0. Message needs to be terminated with ynl_msg_end().
> + */
> + nlh->nlmsg_pid = YNL_SOCKET_BUFFER_SIZE;
> +
> return nlh;
> }
>
> +static int ynl_msg_end(struct ynl_sock *ys, struct nlmsghdr *nlh)
> +{
> + /* We stash buffer length on nlmsg_pid */
> + if (nlh->nlmsg_pid == 0) {
> + yerr(ys, YNL_ERROR_INPUT_INVALID,
> + "Unknwon input buffer lenght");
Typo: lenght -> length
> + return -EINVAL;
> + }
> + if (nlh->nlmsg_pid == YNL_MSG_OVERFLOW) {
> + yerr(ys, YNL_ERROR_INPUT_TOO_BIG,
> + "Constructred message longer than internal buffer");
> + return -EMSGSIZE;
> + }
> +
> + nlh->nlmsg_pid = 0;
> + return 0;
> +}
> +
> struct nlmsghdr *
> ynl_gemsg_start(struct ynl_sock *ys, __u32 id, __u16 flags,
> __u8 cmd, __u8 version)
> @@ -606,6 +630,10 @@ static int ynl_sock_read_family(struct ynl_sock *ys, const char *family_name)
> nlh = ynl_gemsg_start_req(ys, GENL_ID_CTRL, CTRL_CMD_GETFAMILY, 1);
> ynl_attr_put_str(nlh, CTRL_ATTR_FAMILY_NAME, family_name);
>
> + err = ynl_msg_end(ys, nlh);
> + if (err < 0)
> + return err;
> +
> err = send(ys->socket, nlh, nlh->nlmsg_len, 0);
> if (err < 0) {
> perr(ys, "failed to request socket family info");
> @@ -867,6 +895,10 @@ int ynl_exec(struct ynl_sock *ys, struct nlmsghdr *req_nlh,
> {
> int err;
>
> + err = ynl_msg_end(ys, req_nlh);
> + if (err < 0)
> + return err;
> +
> err = send(ys->socket, req_nlh, req_nlh->nlmsg_len, 0);
> if (err < 0)
> return err;
> @@ -920,6 +952,10 @@ int ynl_exec_dump(struct ynl_sock *ys, struct nlmsghdr *req_nlh,
> {
> int err;
>
> + err = ynl_msg_end(ys, req_nlh);
> + if (err < 0)
> + return err;
> +
> err = send(ys->socket, req_nlh, req_nlh->nlmsg_len, 0);
> if (err < 0)
> return err;
> diff --git a/tools/net/ynl/lib/ynl.h b/tools/net/ynl/lib/ynl.h
> index dbeeef8ce91a..9842e85a8c57 100644
> --- a/tools/net/ynl/lib/ynl.h
> +++ b/tools/net/ynl/lib/ynl.h
> @@ -20,6 +20,8 @@ enum ynl_error_code {
> YNL_ERROR_ATTR_INVALID,
> YNL_ERROR_UNKNOWN_NTF,
> YNL_ERROR_INV_RESP,
> + YNL_ERROR_INPUT_INVALID,
> + YNL_ERROR_INPUT_TOO_BIG,
> };
>
> /**
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