diff options
Diffstat (limited to 'src/dkim_transport.c')
| -rw-r--r-- | src/dkim_transport.c | 412 |
1 files changed, 412 insertions, 0 deletions
diff --git a/src/dkim_transport.c b/src/dkim_transport.c new file mode 100644 index 0000000..cfd4b90 --- /dev/null +++ b/src/dkim_transport.c @@ -0,0 +1,412 @@ +/************************************************* +* Exim - an Internet mail transport agent * +*************************************************/ + +/* Copyright (c) The Exim Maintainers 2022 */ +/* Copyright (c) University of Cambridge 1995 - 2018 */ +/* See the file NOTICE for conditions of use and distribution. */ + +/* Transport shim for dkim signing */ + + +#include "exim.h" + +#ifndef DISABLE_DKIM /* rest of file */ + + +static BOOL +dkt_sign_fail(struct ob_dkim * dkim, int * errp) +{ +if (dkim->dkim_strict) + { + uschar * dkim_strict_result = expand_string(dkim->dkim_strict); + + if (dkim_strict_result) + if ( strcmpic(dkim_strict_result, US"1") == 0 + || strcmpic(dkim_strict_result, US"true") == 0) + { + /* Set errno to something halfway meaningful */ + *errp = EACCES; + log_write(0, LOG_MAIN, "DKIM: message could not be signed," + " and dkim_strict is set. Deferring message delivery."); + return FALSE; + } + } +return TRUE; +} + +/* Send the file at in_fd down the output fd */ + +static BOOL +dkt_send_file(int out_fd, int in_fd, off_t off +#ifdef OS_SENDFILE + , size_t size +#endif + ) +{ +#ifdef OS_SENDFILE +DEBUG(D_transport) debug_printf("send file fd=%d size=%u\n", out_fd, (unsigned)(size - off)); +#else +DEBUG(D_transport) debug_printf("send file fd=%d\n", out_fd); +#endif + +/*XXX should implement timeout, like transport_write_block_fd() ? */ + +#ifdef OS_SENDFILE +/* We can use sendfile() to shove the file contents + to the socket. However only if we don't use TLS, + as then there's another layer of indirection + before the data finally hits the socket. */ +if (tls_out.active.sock != out_fd) + { + ssize_t copied = 0; + + while(copied >= 0 && off < size) + copied = os_sendfile(out_fd, in_fd, &off, size - off); + if (copied < 0) + return FALSE; + } +else + +#endif + + { + int sread, wwritten; + + /* Rewind file */ + if (lseek(in_fd, off, SEEK_SET) < 0) return FALSE; + + /* Send file down the original fd */ + while((sread = read(in_fd, deliver_out_buffer, DELIVER_OUT_BUFFER_SIZE)) > 0) + { + uschar * p = deliver_out_buffer; + /* write the chunk */ + + while (sread) + { +#ifndef DISABLE_TLS + wwritten = tls_out.active.sock == out_fd + ? tls_write(tls_out.active.tls_ctx, p, sread, FALSE) + : write(out_fd, CS p, sread); +#else + wwritten = write(out_fd, CS p, sread); +#endif + if (wwritten == -1) + return FALSE; + p += wwritten; + sread -= wwritten; + } + } + + if (sread == -1) + return FALSE; + } + +return TRUE; +} + + + + +/* This function is a wrapper around transport_write_message(). + It is only called from the smtp transport if DKIM or Domainkeys support + is active and no transport filter is to be used. + +Arguments: + As for transport_write_message() in transort.c, with additional arguments + for DKIM. + +Returns: TRUE on success; FALSE (with errno) for any failure +*/ + +static BOOL +dkt_direct(transport_ctx * tctx, struct ob_dkim * dkim, + const uschar ** err) +{ +int save_fd = tctx->u.fd; +int save_options = tctx->options; +BOOL save_wireformat = f.spool_file_wireformat; +uschar * hdrs; +gstring * dkim_signature; +int hsize; +const uschar * errstr; +BOOL rc; + +DEBUG(D_transport) debug_printf("dkim signing direct-mode\n"); + +/* Get headers in string for signing and transmission. Do CRLF +and dotstuffing (but no body nor dot-termination) */ + +tctx->u.msg = NULL; +tctx->options = tctx->options & ~(topt_end_dot | topt_use_bdat) + | topt_output_string | topt_no_body; + +rc = transport_write_message(tctx, 0); +hdrs = string_from_gstring(tctx->u.msg); +hsize = tctx->u.msg->ptr; + +tctx->u.fd = save_fd; +tctx->options = save_options; +if (!rc) return FALSE; + +/* Get signatures for headers plus spool data file */ + +#ifdef EXPERIMENTAL_ARC +arc_sign_init(); +#endif + +/* The dotstuffed status of the datafile depends on whether it was stored +in wireformat. */ + +dkim->dot_stuffed = f.spool_file_wireformat; +if (!(dkim_signature = dkim_exim_sign(deliver_datafile, SPOOL_DATA_START_OFFSET, + hdrs, dkim, &errstr))) + if (!(rc = dkt_sign_fail(dkim, &errno))) + { + *err = errstr; + return FALSE; + } + +#ifdef EXPERIMENTAL_ARC +if (dkim->arc_signspec) /* Prepend ARC headers */ + { + uschar * e = NULL; + if (!(dkim_signature = arc_sign(dkim->arc_signspec, dkim_signature, &e))) + { + *err = e; + return FALSE; + } + } +#endif + +/* Write the signature and headers into the deliver-out-buffer. This should +mean they go out in the same packet as the MAIL, RCPT and (first) BDAT commands +(transport_write_message() sizes the BDAT for the buffered amount) - for short +messages, the BDAT LAST command. We want no dotstuffing expansion here, it +having already been done - but we have to say we want CRLF output format, and +temporarily set the marker for possible already-CRLF input. */ + +tctx->options &= ~topt_escape_headers; +f.spool_file_wireformat = TRUE; +transport_write_reset(0); +if ( ( dkim_signature + && dkim_signature->ptr > 0 + && !write_chunk(tctx, dkim_signature->s, dkim_signature->ptr) + ) + || !write_chunk(tctx, hdrs, hsize) + ) + return FALSE; + +f.spool_file_wireformat = save_wireformat; +tctx->options = save_options | topt_no_headers | topt_continuation; + +if (!(transport_write_message(tctx, 0))) + return FALSE; + +tctx->options = save_options; +return TRUE; +} + + +/* This function is a wrapper around transport_write_message(). + It is only called from the smtp transport if DKIM or Domainkeys support + is active and a transport filter is to be used. The function sets up a + replacement fd into a -K file, then calls the normal function. This way, the + exact bits that exim would have put "on the wire" will end up in the file + (except for TLS encapsulation, which is the very very last thing). When we + are done signing the file, send the signed message down the original fd (or + TLS fd). + +Arguments: + As for transport_write_message() in transort.c, with additional arguments + for DKIM. + +Returns: TRUE on success; FALSE (with errno) for any failure +*/ + +static BOOL +dkt_via_kfile(transport_ctx * tctx, struct ob_dkim * dkim, const uschar ** err) +{ +int dkim_fd; +int save_errno = 0; +BOOL rc; +uschar * dkim_spool_name; +gstring * dkim_signature; +int options, dlen; +off_t k_file_size; +const uschar * errstr; + +dkim_spool_name = spool_fname(US"input", message_subdir, message_id, + string_sprintf("-%d-K", (int)getpid())); + +DEBUG(D_transport) debug_printf("dkim signing via file %s\n", dkim_spool_name); + +if ((dkim_fd = Uopen(dkim_spool_name, O_RDWR|O_CREAT|O_TRUNC, SPOOL_MODE)) < 0) + { + /* Can't create spool file. Ugh. */ + rc = FALSE; + save_errno = errno; + *err = string_sprintf("dkim spoolfile create: %s", strerror(errno)); + goto CLEANUP; + } + +/* Call transport utility function to write the -K file; does the CRLF expansion +(but, in the CHUNKING case, neither dot-stuffing nor dot-termination). */ + + { + int save_fd = tctx->u.fd; + tctx->u.fd = dkim_fd; + options = tctx->options; + tctx->options &= ~topt_use_bdat; + + rc = transport_write_message(tctx, 0); + + tctx->u.fd = save_fd; + tctx->options = options; + } + +/* Save error state. We must clean up before returning. */ +if (!rc) + { + save_errno = errno; + goto CLEANUP; + } + +#ifdef EXPERIMENTAL_ARC +arc_sign_init(); +#endif + +/* Feed the file to the goats^W DKIM lib. At this point the dotstuffed +status of the file depends on the output of transport_write_message() just +above, which should be the result of the end_dot flag in tctx->options. */ + +dkim->dot_stuffed = !!(options & topt_end_dot); +if (!(dkim_signature = dkim_exim_sign(dkim_fd, 0, NULL, dkim, &errstr))) + { + dlen = 0; + if (!(rc = dkt_sign_fail(dkim, &save_errno))) + { + *err = errstr; + goto CLEANUP; + } + } +else + dlen = dkim_signature->ptr; + +#ifdef EXPERIMENTAL_ARC +if (dkim->arc_signspec) /* Prepend ARC headers */ + { + if (!(dkim_signature = arc_sign(dkim->arc_signspec, dkim_signature, USS err))) + goto CLEANUP; + dlen = dkim_signature->ptr; + } +#endif + +#ifndef OS_SENDFILE +if (options & topt_use_bdat) +#endif + if ((k_file_size = lseek(dkim_fd, 0, SEEK_END)) < 0) + { + *err = string_sprintf("dkim spoolfile seek: %s", strerror(errno)); + goto CLEANUP; + } + +if (options & topt_use_bdat) + { + /* On big messages output a precursor chunk to get any pipelined + MAIL & RCPT commands flushed, then reap the responses so we can + error out on RCPT rejects before sending megabytes. */ + + if ( dlen + k_file_size > DELIVER_OUT_BUFFER_SIZE + && dlen > 0) + { + if ( tctx->chunk_cb(tctx, dlen, 0) != OK + || !transport_write_block(tctx, + dkim_signature->s, dlen, FALSE) + || tctx->chunk_cb(tctx, 0, tc_reap_prev) != OK + ) + goto err; + dlen = 0; + } + + /* Send the BDAT command for the entire message, as a single LAST-marked + chunk. */ + + if (tctx->chunk_cb(tctx, dlen + k_file_size, tc_chunk_last) != OK) + goto err; + } + +if(dlen > 0 && !transport_write_block(tctx, dkim_signature->s, dlen, TRUE)) + goto err; + +if (!dkt_send_file(tctx->u.fd, dkim_fd, 0 +#ifdef OS_SENDFILE + , k_file_size +#endif + )) + { + save_errno = errno; + rc = FALSE; + } + +CLEANUP: + /* unlink -K file */ + if (dkim_fd >= 0) (void)close(dkim_fd); + Uunlink(dkim_spool_name); + errno = save_errno; + return rc; + +err: + save_errno = errno; + rc = FALSE; + goto CLEANUP; +} + + + +/*************************************************************************************************** +* External interface to write the message, while signing it with DKIM and/or Domainkeys * +***************************************************************************************************/ + +/* This function is a wrapper around transport_write_message(). + It is only called from the smtp transport if DKIM or Domainkeys support + is compiled in. + +Arguments: + As for transport_write_message() in transort.c, with additional arguments + for DKIM. + +Returns: TRUE on success; FALSE (with errno) for any failure +*/ + +BOOL +dkim_transport_write_message(transport_ctx * tctx, + struct ob_dkim * dkim, const uschar ** err) +{ +/* If we can't sign, just call the original function. */ + +if ( !(dkim->dkim_private_key && dkim->dkim_domain && dkim->dkim_selector) + && !dkim->force_bodyhash) + return transport_write_message(tctx, 0); + +/* If there is no filter command set up, construct the message and calculate +a dkim signature of it, send the signature and a reconstructed message. This +avoids using a temprary file. */ + +if ( !transport_filter_argv + || !*transport_filter_argv + || !**transport_filter_argv + ) + return dkt_direct(tctx, dkim, err); + +/* Use the transport path to write a file, calculate a dkim signature, +send the signature and then send the file. */ + +return dkt_via_kfile(tctx, dkim, err); +} + +#endif /* whole file */ + +/* vi: aw ai sw=2 +*/ +/* End of dkim_transport.c */ |