wireless: add utility function to get P2P attribute

Parsing the P2P attributes can be tricky as their
contents can be split across multiple (vendor) IEs.
Thus, it's not possible to parse them like IEs (by
returning a pointer to the data.) Instead, provide
a function that copies the attribute data into a
caller-provided buffer and returns the size needed
(useful in case the buffer was too small.)

Signed-off-by: Johannes Berg <johannes.berg@intel.com>

1 files changed, 99 insertions, 0 deletions

diff --git a/net/wireless/util.c b/net/wireless/util.c
index 5b6c1df72f31..b99f01cda1f6 100644
--- a/net/wireless/util.c
+++ b/net/wireless/util.c
@@ -980,6 +980,105 @@ u32 cfg80211_calculate_bitrate(struct rate_info *rate)
 }
 EXPORT_SYMBOL(cfg80211_calculate_bitrate);
 
+unsigned int cfg80211_get_p2p_attr(const u8 *ies, unsigned int len,
+                                   u8 attr, u8 *buf, unsigned int bufsize)
+{
+        u8 *out = buf;
+        u16 attr_remaining = 0;
+        bool desired_attr = false;
+        u16 desired_len = 0;
+
+        while (len > 0) {
+                unsigned int iedatalen;
+                unsigned int copy;
+                const u8 *iedata;
+
+                if (len < 2)
+                        return -EILSEQ;
+                iedatalen = ies[1];
+                if (iedatalen + 2 > len)
+                        return -EILSEQ;
+
+                if (ies[0] != WLAN_EID_VENDOR_SPECIFIC)
+                        goto cont;
+
+                if (iedatalen < 4)
+                        goto cont;
+
+                iedata = ies + 2;
+
+                /* check WFA OUI, P2P subtype */
+                if (iedata[0] != 0x50 || iedata[1] != 0x6f ||
+                    iedata[2] != 0x9a || iedata[3] != 0x09)
+                        goto cont;
+
+                iedatalen -= 4;
+                iedata += 4;
+
+                /* check attribute continuation into this IE */
+                copy = min_t(unsigned int, attr_remaining, iedatalen);
+                if (copy && desired_attr) {
+                        desired_len += copy;
+                        if (out) {
+                                memcpy(out, iedata, min(bufsize, copy));
+                                out += min(bufsize, copy);
+                                bufsize -= min(bufsize, copy);
+                        }
+
+
+                        if (copy == attr_remaining)
+                                return desired_len;
+                }
+
+                attr_remaining -= copy;
+                if (attr_remaining)
+                        goto cont;
+
+                iedatalen -= copy;
+                iedata += copy;
+
+                while (iedatalen > 0) {
+                        u16 attr_len;
+
+                        /* P2P attribute ID & size must fit */
+                        if (iedatalen < 3)
+                                return -EILSEQ;
+                        desired_attr = iedata[0] == attr;
+                        attr_len = get_unaligned_le16(iedata + 1);
+                        iedatalen -= 3;
+                        iedata += 3;
+
+                        copy = min_t(unsigned int, attr_len, iedatalen);
+
+                        if (desired_attr) {
+                                desired_len += copy;
+                                if (out) {
+                                        memcpy(out, iedata, min(bufsize, copy));
+                                        out += min(bufsize, copy);
+                                        bufsize -= min(bufsize, copy);
+                                }
+
+                                if (copy == attr_len)
+                                        return desired_len;
+                        }
+
+                        iedata += copy;
+                        iedatalen -= copy;
+                        attr_remaining = attr_len - copy;
+                }
+
+ cont:
+                len -= ies[1] + 2;
+                ies += ies[1] + 2;
+        }
+
+        if (attr_remaining && desired_attr)
+                return -EILSEQ;
+
+        return -ENOENT;
+}
+EXPORT_SYMBOL(cfg80211_get_p2p_attr);
+
 int cfg80211_validate_beacon_int(struct cfg80211_registered_device *rdev,
                                  u32 beacon_int)
 {