tools: ynl: check for overflow of constructed messages

Donald points out that we don't check for overflows.
Stash the length of the message on nlmsg_pid (nlmsg_seq would
do as well). This allows the attribute helpers to remain
self-contained (no extra arguments). Also let the put
helpers continue to return nothing. The error is checked
only in (newly introduced) ynl_msg_end().

Reviewed-by: Donald Hunter <donald.hunter@gmail.com>
Link: https://lore.kernel.org/r/20240305185000.964773-1-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/tools/net/ynl/lib/ynl-priv.h b/tools/net/ynl/lib/ynl-priv.h
index a8099fab035decb75759ee14b50718125c719804..6cf890080dc0921710b37dd6d442591dc9b502da 100644 (file)
--- 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 +241,29 @@ 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;
+
+       /* ynl_msg_start() stashed buffer length in nlmsg_pid. */
+       o = nlh->nlmsg_len + NLA_HDRLEN + NLMSG_ALIGN(size) > nlh->nlmsg_pid;
+       if (o)
+               /* YNL_MSG_OVERFLOW is < NLMSG_HDRLEN, all subsequent checks
+                * are guaranteed to fail.
+                */
+               nlh->nlmsg_pid = YNL_MSG_OVERFLOW;
+       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;
+
        attr = ynl_nlmsg_end_addr(nlh);
        attr->nla_type = attr_type | NLA_F_NESTED;
        nlh->nlmsg_len += NLA_HDRLEN;
@@ -263,6 +283,9 @@ 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 +299,17 @@ 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 484070492b17268c1ccf32a4c58ce91de7618044..b9e77af5af5fa266331e1e6ac3bafb358bbd2113 100644 (file)
--- 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 in nlmsg_pid. */
+       if (nlh->nlmsg_pid == 0) {
+               yerr(ys, YNL_ERROR_INPUT_INVALID,
+                    "Unknown input buffer 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)
@@ -607,6 +631,10 @@ 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");
@@ -868,6 +896,10 @@ 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;
@@ -921,6 +953,10 @@ 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 dbeeef8ce91aad76de6f9f92d216e92351e6c53e..9842e85a8c57da5104833ae2a7794c2285de8db3 100644 (file)
--- 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,
 };
 
 /**