neocgit

a more 'modern' version of cgit
Log | Files | Refs | Submodules | README | LICENSE | git clone https://git.ne02ptzero.me/git/neocgit

commit b826537cb4aa2358027ffcb1dd6a87274734e962
parent d6e9200cc35411f3f27426b608bcfdef9348e6d3
Author: Jason A. Donenfeld <Jason@zx2c4.com>
Date:   Thu, 16 Jan 2014 11:39:17 +0100

authentication: use hidden form instead of referer

This also gives us some CSRF protection. Note that we make use of the
hmac to protect the redirect value.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

Diffstat:
Mcgit.c | 22++++++++--------------
Mcgitrc.5.txt | 3++-
Mfilters/simple-authentication.lua | 200++++++++++++++++++++++++++++++++++++++++++++++++-------------------------------
3 files changed, 131 insertions(+), 94 deletions(-)

diff --git a/cgit.c b/cgit.c @@ -614,22 +614,19 @@ static inline void open_auth_filter(struct cgit_context *ctx, const char *functi ctx->qry.url ? ctx->qry.url : ""); } +/* We intentionally keep this rather small, instead of looping and + * feeding it to the filter a couple bytes at a time. This way, the + * filter itself does not need to handle any denial of service or + * buffer bloat issues. If this winds up being too small, people + * will complain on the mailing list, and we'll increase it as needed. */ #define MAX_AUTHENTICATION_POST_BYTES 4096 +/* The filter is expected to spit out "Status: " and all headers. */ static inline void authenticate_post(struct cgit_context *ctx) { - if (ctx->env.http_referer && strlen(ctx->env.http_referer) > 0) { - html("Status: 302 Redirect\n"); - html("Cache-Control: no-cache, no-store\n"); - htmlf("Location: %s\n", ctx->env.http_referer); - } else { - html("Status: 501 Missing Referer\n"); - html("Cache-Control: no-cache, no-store\n\n"); - exit(0); - } - - open_auth_filter(ctx, "authenticate-post"); char buffer[MAX_AUTHENTICATION_POST_BYTES]; int len; + + open_auth_filter(ctx, "authenticate-post"); len = ctx->env.content_length; if (len > MAX_AUTHENTICATION_POST_BYTES) len = MAX_AUTHENTICATION_POST_BYTES; @@ -637,10 +634,7 @@ static inline void authenticate_post(struct cgit_context *ctx) die_errno("Could not read POST from stdin"); if (write(STDOUT_FILENO, buffer, len) < 0) die_errno("Could not write POST to stdout"); - /* The filter may now spit out a Set-Cookie: ... */ cgit_close_filter(ctx->cfg.auth_filter); - - html("\n"); exit(0); } diff --git a/cgitrc.5.txt b/cgitrc.5.txt @@ -662,7 +662,8 @@ auth filter:: the http cookie and return a 0 if it is invalid or 1 if it is invalid, in the exit code / close function. If the filter action is "authenticate-post", this filter receives POST'd parameters on - standard input, and should write to output one or more "Set-Cookie" + standard input, and should write a complete CGI request, preferably + with a 302 redirect, and write to output one or more "Set-Cookie" HTTP headers, each followed by a newline. Please see `filters/simple-authentication.lua` for a clear example diff --git a/filters/simple-authentication.lua b/filters/simple-authentication.lua @@ -33,15 +33,28 @@ local secret = "BE SURE TO CUSTOMIZE THIS STRING TO SOMETHING BIG AND RANDOM" -- -- --- Sets HTTP cookie headers based on post +-- Sets HTTP cookie headers based on post and sets up redirection. function authenticate_post() local password = users[post["username"]] - -- TODO: Implement time invariant string comparison function to mitigate against timing attack. + local redirect = validate_value(post["redirect"]) + + if redirect == nil then + not_found() + return 0 + end + + redirect_to(redirect) + + -- TODO: Implement time invariant string comparison function to mitigate timing attack. if password == nil or password ~= post["password"] then - construct_cookie("", "cgitauth") + set_cookie("cgitauth", "") else - construct_cookie(post["username"], "cgitauth") + -- One week expiration time + local username = secure_value(post["username"], os.time() + 604800) + set_cookie("cgitauth", username) end + + html("\n") return 0 end @@ -54,8 +67,8 @@ function authenticate_cookie() return 1 end - local username = validate_cookie(get_cookie(http["cookie"], "cgitauth")) - if username == nil or not accepted_users[username] then + local username = validate_value(get_cookie(http["cookie"], "cgitauth")) + if username == nil or not accepted_users[username:lower()] then return 0 else return 1 @@ -68,6 +81,9 @@ function body() html("<form method='post' action='") html_attr(cgit["login"]) html("'>") + html("<input type='hidden' name='redirect' value='") + html_attr(secure_value(cgit["url"], 0)) + html("' />") html("<table>") html("<tr><td><label for='username'>Username:</label></td><td><input id='username' name='username' autofocus /></td></tr>") html("<tr><td><label for='password'>Password:</label></td><td><input id='password' name='password' type='password' /></td></tr>") @@ -78,81 +94,10 @@ function body() end --- --- --- Cookie construction and validation helpers. --- --- - -local crypto = require("crypto") - --- Returns username of cookie if cookie is valid. Otherwise returns nil. -function validate_cookie(cookie) - local i = 0 - local username = "" - local expiration = 0 - local salt = "" - local hmac = "" - - if cookie:len() < 3 or cookie:sub(1, 1) == "|" then - return nil - end - - for component in string.gmatch(cookie, "[^|]+") do - if i == 0 then - username = component - elseif i == 1 then - expiration = tonumber(component) - if expiration == nil then - expiration = 0 - end - elseif i == 2 then - salt = component - elseif i == 3 then - hmac = component - else - break - end - i = i + 1 - end - - if hmac == nil or hmac:len() == 0 then - return nil - end - - -- TODO: implement time invariant comparison to prevent against timing attack. - if hmac ~= crypto.hmac.digest("sha1", username .. "|" .. tostring(expiration) .. "|" .. salt, secret) then - return nil - end - - if expiration <= os.time() then - return nil - end - - return username:lower() -end - -function construct_cookie(username, cookie) - local authstr = "" - if username:len() > 0 then - -- One week expiration time - local expiration = os.time() + 604800 - local salt = crypto.hex(crypto.rand.bytes(16)) - - authstr = username .. "|" .. tostring(expiration) .. "|" .. salt - authstr = authstr .. "|" .. crypto.hmac.digest("sha1", authstr, secret) - end - - html("Set-Cookie: " .. cookie .. "=" .. authstr .. "; HttpOnly") - if http["https"] == "yes" or http["https"] == "on" or http["https"] == "1" then - html("; secure") - end - html("\n") -end -- -- --- Wrapper around filter API follows below, exposing the http table, the cgit table, and the post table to the above functions. +-- Wrapper around filter API, exposing the http table, the cgit table, and the post table to the above functions. -- -- @@ -197,7 +142,7 @@ end -- -- --- Utility functions follow below, based on keplerproject/wsapi. +-- Utility functions based on keplerproject/wsapi. -- -- @@ -211,6 +156,16 @@ function url_decode(str) return str end +function url_encode(str) + if not str then + return "" + end + str = string.gsub(str, "\n", "\r\n") + str = string.gsub(str, "([^%w ])", function (c) return string.format("%%%02X", string.byte(c)) end) + str = string.gsub(str, " ", "+") + return str +end + function parse_qs(qs) local tab = {} for key, val in string.gmatch(qs, "([^&=]+)=([^&=]*)&?") do @@ -223,3 +178,90 @@ function get_cookie(cookies, name) cookies = string.gsub(";" .. cookies .. ";", "%s*;%s*", ";") return url_decode(string.match(cookies, ";" .. name .. "=(.-);")) end + + +-- +-- +-- Cookie construction and validation helpers. +-- +-- + +local crypto = require("crypto") + +-- Returns value of cookie if cookie is valid. Otherwise returns nil. +function validate_value(cookie) + local i = 0 + local value = "" + local expiration = 0 + local salt = "" + local hmac = "" + + if cookie == nil or cookie:len() < 3 or cookie:sub(1, 1) == "|" then + return nil + end + + for component in string.gmatch(cookie, "[^|]+") do + if i == 0 then + value = component + elseif i == 1 then + expiration = tonumber(component) + if expiration == nil then + expiration = 0 + end + elseif i == 2 then + salt = component + elseif i == 3 then + hmac = component + else + break + end + i = i + 1 + end + + if hmac == nil or hmac:len() == 0 then + return nil + end + + -- TODO: implement time invariant comparison to prevent against timing attack. + if hmac ~= crypto.hmac.digest("sha1", value .. "|" .. tostring(expiration) .. "|" .. salt, secret) then + return nil + end + + if expiration ~= 0 and expiration <= os.time() then + return nil + end + + return url_decode(value) +end + +function secure_value(value, expiration) + if value == nil or value:len() <= 0 then + return "" + end + + local authstr = "" + local salt = crypto.hex(crypto.rand.bytes(16)) + value = url_encode(value) + authstr = value .. "|" .. tostring(expiration) .. "|" .. salt + authstr = authstr .. "|" .. crypto.hmac.digest("sha1", authstr, secret) + return authstr +end + +function set_cookie(cookie, value) + html("Set-Cookie: " .. cookie .. "=" .. value .. "; HttpOnly") + if http["https"] == "yes" or http["https"] == "on" or http["https"] == "1" then + html("; secure") + end + html("\n") +end + +function redirect_to(url) + html("Status: 302 Redirect\n") + html("Cache-Control: no-cache, no-store\n") + html("Location: " .. url .. "\n") +end + +function not_found() + html("Status: 404 Not Found\n") + html("Cache-Control: no-cache, no-store\n\n") +end