Re: [PATCH v4 1/2] git-imap-send: Add CRAM-MD5 authenticate method support
From: Junio C Hamano <hidden>
Date: 2016-06-15 22:48:17
Junio C Hamano [off-list ref] writes:
If you know the length of the decoded thing, then you would just know how much to hash. Doesn't the EVP_DecodeBlock() give you that number? Why do you need a NUL termination to begin with? Because you pretend as if you do not have the actual length, you run strlen() instead. I am not that familiar with the API to EVP_* functions, but I'd be surprised if it were designed in such a stupid way to force you to write into a pre-zeroed buffer. By the way, if you use strlen() on a pre-cleared and overallocated buffer, doesn't your ENCODED_SIZE(n) have to be one byte longer than what you are computing? Looking for EVP_DecodeBlock in http://www.google.com/codesearch seems to find usage examples of varying quality. Your favorite isync-0.5 stores the result in "len", but it entirely ignores it and does the same silly calloc() and strlen(). Usage example in OpenSSL's own x509spki stores the return value in spki_len and uses that as the length of the stuff to call another function, which looks much more reasonable. From this observation and a bit of reading of the manual, my understanding is that the function gives you the number of bytes written in the buffer. So does EncodeBlock(), I would think.
So here is a replacement version to see if I remember all the points raised in the thread. * Use of HMAC_Init() is kept, so people with ancient OpenSSL can use it; * Lose "overallocate with xcalloc() and use strlen() to see how long the result is" pattern; EVP_DecodeBlock() and EVP_EncodeBlock() should be returning the length anyway, so use that directly; * Comment style fixes; * Lose "fprintf() then exit()"; die() instead; and * Call HMAC_CTX_cleanup() when done; I didn't check the validity of the last one at all. Please see if there is any funnies. -- >8 -- Subject: imap-send: support CRAM-MD5 authentication CRAM-MD5 authentication ought to be independent from SSL, but NO_OPENSSL build will not support this because the base64 and md5 code are used from the OpenSSL library in this implementation. Signed-off-by: Hitoshi Mitake <redacted> Signed-off-by: Junio C Hamano <redacted> --- Documentation/git-imap-send.txt | 4 + imap-send.c | 146 +++++++++++++++++++++++++++++++++++---- 2 files changed, 135 insertions(+), 15 deletions(-)
diff --git a/Documentation/git-imap-send.txt b/Documentation/git-imap-send.txt
index 57db955..6cafbe2 100644
--- a/Documentation/git-imap-send.txt
+++ b/Documentation/git-imap-send.txt@@ -71,6 +71,10 @@ imap.preformattedHTML:: option causes Thunderbird to send the patch as a plain/text, format=fixed email. Default is `false`. +imap.authMethod:: + Specify authenticate method for authentication with IMAP server. + Current supported method is 'CRAM-MD5' only. + Examples ~~~~~~~~
diff --git a/imap-send.c b/imap-send.c
index ba72fa4..bf1cd73 100644
--- a/imap-send.c
+++ b/imap-send.c@@ -27,6 +27,9 @@ #include "run-command.h" #ifdef NO_OPENSSL typedef void *SSL; +#else +#include <openssl/evp.h> +#include <openssl/hmac.h> #endif struct store_conf {
@@ -140,6 +143,20 @@ struct imap_server_conf { int use_ssl; int ssl_verify; int use_html; + char *auth_method; +}; + +static struct imap_server_conf server = { + NULL, /* name */ + NULL, /* tunnel */ + NULL, /* host */ + 0, /* port */ + NULL, /* user */ + NULL, /* pass */ + 0, /* use_ssl */ + 1, /* ssl_verify */ + 0, /* use_html */ + NULL, /* auth_method */ }; struct imap_store_conf {
@@ -214,6 +231,7 @@ enum CAPABILITY { LITERALPLUS, NAMESPACE, STARTTLS, + AUTH_CRAM_MD5, }; static const char *cap_list[] = {
@@ -222,6 +240,7 @@ static const char *cap_list[] = { "LITERAL+", "NAMESPACE", "STARTTLS", + "AUTH=CRAM-MD5", }; #define RESP_OK 0
@@ -949,6 +968,87 @@ static void imap_close_store(struct store *ctx) free(ctx); } +#ifndef NO_OPENSSL + +/* + * hexchar() and cram() functions are based on the code from the isync + * project (http://isync.sf.net/). + */ +static char hexchar(unsigned int b) +{ + return b < 10 ? '0' + b : 'a' + (b - 10); +} + +#define ENCODED_SIZE(n) (4*((n+2)/3)) +static char *cram(const char *challenge_64, const char *user, const char *pass) +{ + int i, resp_len, encoded_len, decoded_len; + HMAC_CTX hmac; + unsigned char hash[16]; + char hex[33]; + char *response, *response_64, *challenge; + + /* + * length of challenge_64 (i.e. base-64 encoded string) is a good + * enough upper bound for challenge (decoded result). + */ + encoded_len = strlen(challenge_64); + challenge = xmalloc(encoded_len); + decoded_len = EVP_DecodeBlock((unsigned char *)challenge, + (unsigned char *)challenge_64, encoded_len); + if (decoded_len < 0) + die("invalid challenge %s", challenge_64); + HMAC_Init(&hmac, (unsigned char *)pass, strlen(pass), EVP_md5()); + HMAC_Update(&hmac, (unsigned char *)challenge, decoded_len); + HMAC_Final(&hmac, hash, NULL); + HMAC_CTX_cleanup(&hmac); + + hex[32] = 0; + for (i = 0; i < 16; i++) { + hex[2 * i] = hexchar((hash[i] >> 4) & 0xf); + hex[2 * i + 1] = hexchar(hash[i] & 0xf); + } + + /* response: "<user> <digest in hex>" */ + resp_len = strlen(user) + 1 + strlen(hex) + 1; + response = xmalloc(resp_len); + sprintf(response, "%s %s", user, hex); + + response_64 = xmalloc(ENCODED_SIZE(resp_len)); + encoded_len = EVP_EncodeBlock((unsigned char *)response_64, + (unsigned char *)response, resp_len); + if (encoded_len < 0) + die("EVP_EncodeBlock error"); + response_64[encoded_len] = '\0'; + return (char *)response_64; +} + +#else + +static char *cram(const char *challenge_64, const char *user, const char *pass) +{ + die("If you want to use CRAM-MD5 authenticate method, " + "you have to build git-imap-send with OpenSSL library."); +} + +#endif + +static int auth_cram_md5(struct imap_store *ctx, struct imap_cmd *cmd, const char *prompt) +{ + int ret; + char *response; + + response = cram(prompt, server.user, server.pass); + + ret = socket_write(&ctx->imap->buf.sock, response, strlen(response)); + if (ret != strlen(response)) + return error("IMAP error: sending response failed\n"); + + free(response); + + return 0; +} + static struct store *imap_open_store(struct imap_server_conf *srvc) { struct imap_store *ctx;
@@ -1130,9 +1230,34 @@ static struct store *imap_open_store(struct imap_server_conf *srvc) if (!imap->buf.sock.ssl) imap_warn("*** IMAP Warning *** Password is being " "sent in the clear\n"); - if (imap_exec(ctx, NULL, "LOGIN \"%s\" \"%s\"", srvc->user, srvc->pass) != RESP_OK) { - fprintf(stderr, "IMAP error: LOGIN failed\n"); - goto bail; + + if (srvc->auth_method) { + struct imap_cmd_cb cb; + + if (!strcmp(srvc->auth_method, "CRAM-MD5")) { + if (!CAP(AUTH_CRAM_MD5)) { + fprintf(stderr, "You specified" + "CRAM-MD5 as authentication method, " + "but %s doesn't support it.\n", srvc->host); + goto bail; + } + /* CRAM-MD5 */ + + memset(&cb, 0, sizeof(cb)); + cb.cont = auth_cram_md5; + if (imap_exec(ctx, &cb, "AUTHENTICATE CRAM-MD5") != RESP_OK) { + fprintf(stderr, "IMAP error: AUTHENTICATE CRAM-MD5 failed\n"); + goto bail; + } + } else { + fprintf(stderr, "Unknown authentication method:%s\n", srvc->host); + goto bail; + } + } else { + if (imap_exec(ctx, NULL, "LOGIN \"%s\" \"%s\"", srvc->user, srvc->pass) != RESP_OK) { + fprintf(stderr, "IMAP error: LOGIN failed\n"); + goto bail; + } } } /* !preauth */
@@ -1310,18 +1435,6 @@ static int split_msg(struct msg_data *all_msgs, struct msg_data *msg, int *ofs) return 1; } -static struct imap_server_conf server = { - NULL, /* name */ - NULL, /* tunnel */ - NULL, /* host */ - 0, /* port */ - NULL, /* user */ - NULL, /* pass */ - 0, /* use_ssl */ - 1, /* ssl_verify */ - 0, /* use_html */ -}; - static char *imap_folder; static int git_imap_config(const char *key, const char *val, void *cb)
@@ -1361,6 +1474,9 @@ static int git_imap_config(const char *key, const char *val, void *cb) server.port = git_config_int(key, val); else if (!strcmp("tunnel", key)) server.tunnel = xstrdup(val); + else if (!strcmp("authmethod", key)) + server.auth_method = xstrdup(val); + return 0; }