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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-07 16:16:13 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-07 16:16:13 +0000 |
commit | e90fcc54809db2591dc083f43ef54c6ec8c60847 (patch) | |
tree | f20bc206c3c2d5d59d37c46c5cf5d53a20642556 /src/mime.c | |
parent | Initial commit. (diff) | |
download | exim4-e90fcc54809db2591dc083f43ef54c6ec8c60847.tar.xz exim4-e90fcc54809db2591dc083f43ef54c6ec8c60847.zip |
Adding upstream version 4.96.upstream/4.96upstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to '')
-rw-r--r-- | src/mime.c | 803 |
1 files changed, 803 insertions, 0 deletions
diff --git a/src/mime.c b/src/mime.c new file mode 100644 index 0000000..c192199 --- /dev/null +++ b/src/mime.c @@ -0,0 +1,803 @@ +/************************************************* +* Exim - an Internet mail transport agent * +*************************************************/ + +/* + * Copyright (c) The Exim Maintainers 2015 - 2022 + * Copyright (c) Tom Kistner <tom@duncanthrax.net> 2004 - 2015 + * License: GPL + */ + +#include "exim.h" +#ifdef WITH_CONTENT_SCAN /* entire file */ +#include "mime.h" +#include <sys/stat.h> + +FILE *mime_stream = NULL; +uschar *mime_current_boundary = NULL; + +static mime_header mime_header_list[] = { + /* name namelen value */ + { US"content-type:", 13, &mime_content_type }, + { US"content-disposition:", 20, &mime_content_disposition }, + { US"content-transfer-encoding:", 26, &mime_content_transfer_encoding }, + { US"content-id:", 11, &mime_content_id }, + { US"content-description:", 20, &mime_content_description } +}; + +static int mime_header_list_size = nelem(mime_header_list); + +static mime_parameter mime_parameter_list[] = { + /* name namelen value */ + { US"name=", 5, &mime_filename }, + { US"filename=", 9, &mime_filename }, + { US"charset=", 8, &mime_charset }, + { US"boundary=", 9, &mime_boundary } +}; + + +/************************************************* +* set MIME anomaly level + text * +*************************************************/ + +/* Small wrapper to set the two expandables which + give info on detected "problems" in MIME + encodings. Indexes are defined in mime.h. */ + +void +mime_set_anomaly(int idx) +{ +struct anom { + int level; + const uschar * text; +} anom[] = { {1, CUS"Broken Quoted-Printable encoding detected"}, + {2, CUS"Broken BASE64 encoding detected"} }; + +mime_anomaly_level = anom[idx].level; +mime_anomaly_text = anom[idx].text; +} + + +/************************************************* +* decode quoted-printable chars * +*************************************************/ + +/* gets called when we hit a = + returns: new pointer position + result code in c: + -2 - decode error + -1 - soft line break, no char + 0-255 - char to write +*/ + +static uschar * +mime_decode_qp_char(uschar *qp_p, int *c) +{ +uschar *initial_pos = qp_p; + +/* advance one char */ +qp_p++; + +/* Check for two hex digits and decode them */ +if (isxdigit(*qp_p) && isxdigit(qp_p[1])) + { + /* Do hex conversion */ + *c = (isdigit(*qp_p) ? *qp_p - '0' : toupper(*qp_p) - 'A' + 10) <<4; + qp_p++; + *c |= isdigit(*qp_p) ? *qp_p - '0' : toupper(*qp_p) - 'A' + 10; + return qp_p + 1; + } + +/* tab or whitespace may follow just ignore it if it precedes \n */ +while (*qp_p == '\t' || *qp_p == ' ' || *qp_p == '\r') + qp_p++; + +if (*qp_p == '\n') /* hit soft line break */ + { + *c = -1; + return qp_p; + } + +/* illegal char here */ +*c = -2; +return initial_pos; +} + + +/* just dump MIME part without any decoding */ +static ssize_t +mime_decode_asis(FILE* in, FILE* out, uschar* boundary) +{ +ssize_t len, size = 0; +uschar buffer[MIME_MAX_LINE_LENGTH]; + +while(fgets(CS buffer, MIME_MAX_LINE_LENGTH, mime_stream) != NULL) + { + if (boundary != NULL + && Ustrncmp(buffer, "--", 2) == 0 + && Ustrncmp((buffer+2), boundary, Ustrlen(boundary)) == 0 + ) + break; + + len = Ustrlen(buffer); + if (fwrite(buffer, 1, (size_t)len, out) < len) + return -1; + size += len; + } /* while */ +return size; +} + + + +/* decode quoted-printable MIME part */ +static ssize_t +mime_decode_qp(FILE* in, FILE* out, uschar* boundary) +{ +uschar ibuf[MIME_MAX_LINE_LENGTH], obuf[MIME_MAX_LINE_LENGTH]; +uschar *ipos, *opos; +ssize_t len, size = 0; + +while (fgets(CS ibuf, MIME_MAX_LINE_LENGTH, in) != NULL) + { + if (boundary != NULL + && Ustrncmp(ibuf, "--", 2) == 0 + && Ustrncmp((ibuf+2), boundary, Ustrlen(boundary)) == 0 + ) + break; /* todo: check for missing boundary */ + + ipos = ibuf; + opos = obuf; + + while (*ipos != 0) + { + if (*ipos == '=') + { + int decode_qp_result; + + ipos = mime_decode_qp_char(ipos, &decode_qp_result); + + if (decode_qp_result == -2) + { + /* Error from decoder. ipos is unchanged. */ + mime_set_anomaly(MIME_ANOMALY_BROKEN_QP); + *opos++ = '='; + ++ipos; + } + else if (decode_qp_result == -1) + break; + else if (decode_qp_result >= 0) + *opos++ = decode_qp_result; + } + else + *opos++ = *ipos++; + } + /* something to write? */ + len = opos - obuf; + if (len > 0) + { + if (fwrite(obuf, 1, len, out) != len) return -1; /* error */ + size += len; + } + } +return size; +} + + +/* + * Return open filehandle for combo of path and file. + * Side-effect: set mime_decoded_filename, to copy in allocated mem + */ +static FILE * +mime_get_decode_file(uschar *pname, uschar *fname) +{ +if (pname && fname) + mime_decoded_filename = string_sprintf("%s/%s", pname, fname); +else if (!pname) + mime_decoded_filename = string_copy(fname); +else if (!fname) + { + int file_nr = 0; + int result = 0; + + /* must find first free sequential filename */ + do + { + struct stat mystat; + mime_decoded_filename = string_sprintf("%s/%s-%05u", pname, message_id, file_nr++); + /* security break */ + if (file_nr >= 1024) + break; + result = stat(CS mime_decoded_filename, &mystat); + } while(result != -1); + } + +return modefopen(mime_decoded_filename, "wb+", SPOOL_MODE); +} + + +int +mime_decode(const uschar **listptr) +{ +int sep = 0; +const uschar *list = *listptr; +uschar * option; +uschar * decode_path; +FILE *decode_file = NULL; +long f_pos = 0; +ssize_t size_counter = 0; +ssize_t (*decode_function)(FILE*, FILE*, uschar*); + +if (!mime_stream || (f_pos = ftell(mime_stream)) < 0) + return FAIL; + +/* build default decode path (will exist since MBOX must be spooled up) */ +decode_path = string_sprintf("%s/scan/%s", spool_directory, message_id); + +/* try to find 1st option */ +if ((option = string_nextinlist(&list, &sep, NULL, 0))) + { + /* parse 1st option */ + if ((Ustrcmp(option,"false") == 0) || (Ustrcmp(option,"0") == 0)) + /* explicitly no decoding */ + return FAIL; + + if (Ustrcmp(option,"default") == 0) + /* explicit default path + file names */ + goto DEFAULT_PATH; + + if (option[0] == '/') + { + struct stat statbuf; + + memset(&statbuf,0,sizeof(statbuf)); + + /* assume either path or path+file name */ + if ( (stat(CS option, &statbuf) == 0) && S_ISDIR(statbuf.st_mode) ) + /* is directory, use it as decode_path */ + decode_file = mime_get_decode_file(option, NULL); + else + /* does not exist or is a file, use as full file name */ + decode_file = mime_get_decode_file(NULL, option); + } + else + /* assume file name only, use default path */ + decode_file = mime_get_decode_file(decode_path, option); + } +else + { + /* no option? patch default path */ +DEFAULT_PATH: + decode_file = mime_get_decode_file(decode_path, NULL); + } + +if (!decode_file) + return DEFER; + +/* decode according to mime type */ +decode_function = + !mime_content_transfer_encoding + ? mime_decode_asis /* no encoding, dump as-is */ + : Ustrcmp(mime_content_transfer_encoding, "base64") == 0 + ? mime_decode_base64 + : Ustrcmp(mime_content_transfer_encoding, "quoted-printable") == 0 + ? mime_decode_qp + : mime_decode_asis; /* unknown encoding type, just dump as-is */ + +size_counter = decode_function(mime_stream, decode_file, mime_current_boundary); + +clearerr(mime_stream); +if (fseek(mime_stream, f_pos, SEEK_SET)) + return DEFER; + +if (fclose(decode_file) != 0 || size_counter < 0) + return DEFER; + +/* round up to the next KiB */ +mime_content_size = (size_counter + 1023) / 1024; + +return OK; +} + + +static int +mime_get_header(FILE *f, uschar *header) +{ +int c = EOF; +int done = 0; +int header_value_mode = 0; +int header_open_brackets = 0; +int num_copied = 0; + +while(!done) + { + if ((c = fgetc(f)) == EOF) break; + + /* always skip CRs */ + if (c == '\r') continue; + + if (c == '\n') + { + if (num_copied > 0) + { + /* look if next char is '\t' or ' ' */ + if ((c = fgetc(f)) == EOF) break; + if ( (c == '\t') || (c == ' ') ) continue; + (void)ungetc(c,f); + } + /* end of the header, terminate with ';' */ + c = ';'; + done = 1; + } + + /* skip control characters */ + if (c < 32) continue; + + if (header_value_mode) + { + /* --------- value mode ----------- */ + /* skip leading whitespace */ + if ( ((c == '\t') || (c == ' ')) && (header_value_mode == 1) ) + continue; + + /* we have hit a non-whitespace char, start copying value data */ + header_value_mode = 2; + + if (c == '"') /* flip "quoted" mode */ + header_value_mode = header_value_mode==2 ? 3 : 2; + + /* leave value mode on unquoted ';' */ + if (header_value_mode == 2 && c == ';') + header_value_mode = 0; + /* -------------------------------- */ + } + else + { + /* -------- non-value mode -------- */ + /* skip whitespace + tabs */ + if ( (c == ' ') || (c == '\t') ) + continue; + if (c == '\\') + { + /* quote next char. can be used + to escape brackets. */ + if ((c = fgetc(f)) == EOF) break; + } + else if (c == '(') + { + header_open_brackets++; + continue; + } + else if ((c == ')') && header_open_brackets) + { + header_open_brackets--; + continue; + } + else if ( (c == '=') && !header_open_brackets ) /* enter value mode */ + header_value_mode = 1; + + /* skip chars while we are in a comment */ + if (header_open_brackets > 0) + continue; + /* -------------------------------- */ + } + + /* copy the char to the buffer */ + header[num_copied++] = (uschar)c; + + /* break if header buffer is full */ + if (num_copied > MIME_MAX_HEADER_SIZE-1) + done = 1; + } + +if ((num_copied > 0) && (header[num_copied-1] != ';')) + header[num_copied-1] = ';'; + +/* 0-terminate */ +header[num_copied] = '\0'; + +/* return 0 for EOF or empty line */ +return c == EOF || num_copied == 1 ? 0 : 1; +} + + +/* reset all per-part mime variables */ +static void +mime_vars_reset(void) +{ +mime_anomaly_level = 0; +mime_anomaly_text = NULL; +mime_boundary = NULL; +mime_charset = NULL; +mime_decoded_filename = NULL; +mime_filename = NULL; +mime_content_description = NULL; +mime_content_disposition = NULL; +mime_content_id = NULL; +mime_content_transfer_encoding = NULL; +mime_content_type = NULL; +mime_is_multipart = 0; +mime_content_size = 0; +} + + +/* Grab a parameter value, dealing with quoting. + +Arguments: + str Input string. Updated on return to point to terminating ; or NUL + +Return: + Allocated string with parameter value +*/ +static uschar * +mime_param_val(uschar ** sp) +{ +uschar * s = *sp; +gstring * val = NULL; + +/* debug_printf_indent(" considering paramval '%s'\n", s); */ + +while (*s && *s != ';') /* ; terminates */ + if (*s == '"') + { + s++; /* skip opening " */ + while (*s && *s != '"') /* " protects ; */ + val = string_catn(val, s++, 1); + if (*s) s++; /* skip closing " */ + } + else + val = string_catn(val, s++, 1); +*sp = s; +return string_from_gstring(val); +} + +static uschar * +mime_next_semicolon(uschar * s) +{ +while (*s && *s != ';') /* ; terminates */ + if (*s == '"') + { + s++; /* skip opening " */ + while (*s && *s != '"') /* " protects ; */ + s++; + if (*s) s++; /* skip closing " */ + } + else + s++; +return s; +} + + +static uschar * +rfc2231_to_2047(const uschar * fname, const uschar * charset, int * len) +{ +gstring * val = string_catn(NULL, US"=?", 2); +uschar c; + +if (charset) + val = string_cat(val, charset); +val = string_catn(val, US"?Q?", 3); + +while ((c = *fname)) + if (c == '%' && isxdigit(fname[1]) && isxdigit(fname[2])) + { + val = string_catn(val, US"=", 1); + val = string_catn(val, ++fname, 2); + fname += 2; + } + else + val = string_catn(val, fname++, 1); + +val = string_catn(val, US"?=", 2); +*len = val->ptr; +return string_from_gstring(val); +} + + +int +mime_acl_check(uschar *acl, FILE *f, struct mime_boundary_context *context, + uschar **user_msgptr, uschar **log_msgptr) +{ +int rc = OK; +uschar * header = NULL; +struct mime_boundary_context nested_context; + +/* reserve a line buffer to work in. Assume tainted data. */ +header = store_get(MIME_MAX_HEADER_SIZE+1, GET_TAINTED); + +/* Not actually used at the moment, but will be vital to fixing + * some RFC 2046 nonconformance later... */ +nested_context.parent = context; + +/* loop through parts */ +while(1) + { + /* reset all per-part mime variables */ + mime_vars_reset(); + + /* If boundary is null, we assume that *f is positioned on the start of + headers (for example, at the very beginning of a message. If a boundary is + given, we must first advance to it to reach the start of the next header + block. */ + + /* NOTE -- there's an error here -- RFC2046 specifically says to + * check for outer boundaries. This code doesn't do that, and + * I haven't fixed this. + * + * (I have moved partway towards adding support, however, by adding + * a "parent" field to my new boundary-context structure.) + */ + if (context) for (;;) + { + if (!fgets(CS header, MIME_MAX_HEADER_SIZE, f)) + { + /* Hit EOF or read error. Ugh. */ + DEBUG(D_acl) debug_printf_indent("MIME: Hit EOF ...\n"); + return rc; + } + + /* boundary line must start with 2 dashes */ + if ( Ustrncmp(header, "--", 2) == 0 + && Ustrncmp(header+2, context->boundary, Ustrlen(context->boundary)) == 0 + ) + { /* found boundary */ + if (Ustrncmp((header+2+Ustrlen(context->boundary)), "--", 2) == 0) + { + /* END boundary found */ + DEBUG(D_acl) debug_printf_indent("MIME: End boundary found %s\n", + context->boundary); + return rc; + } + + DEBUG(D_acl) debug_printf_indent("MIME: Next part with boundary %s\n", + context->boundary); + break; + } + } + + /* parse headers, set up expansion variables */ + while (mime_get_header(f, header)) + + /* look for interesting headers */ + for (struct mime_header * mh = mime_header_list; + mh < mime_header_list + mime_header_list_size; + mh++) if (strncmpic(mh->name, header, mh->namelen) == 0) + { + uschar * p = header + mh->namelen; + uschar * q; + + /* grab the value (normalize to lower case) + and copy to its corresponding expansion variable */ + + for (q = p; *q != ';' && *q; q++) ; + *mh->value = string_copynlc(p, q-p); + DEBUG(D_acl) debug_printf_indent("MIME: found %s header, value is '%s'\n", + mh->name, *mh->value); + + if (*(p = q)) p++; /* jump past the ; */ + + { + uschar * mime_fname = NULL; + uschar * mime_fname_rfc2231 = NULL; + uschar * mime_filename_charset = NULL; + BOOL decoding_failed = FALSE; + + /* grab all param=value tags on the remaining line, + check if they are interesting */ + + while (*p) + { + DEBUG(D_acl) debug_printf_indent("MIME: considering paramlist '%s'\n", p); + + if ( !mime_filename + && strncmpic(CUS"content-disposition:", header, 20) == 0 + && strncmpic(CUS"filename*", p, 9) == 0 + ) + { /* RFC 2231 filename */ + uschar * q; + + /* find value of the filename */ + p += 9; + while(*p != '=' && *p) p++; + if (*p) p++; /* p is filename or NUL */ + q = mime_param_val(&p); /* p now trailing ; or NUL */ + + if (q && *q) + { + uschar * temp_string, * err_msg; + int slen; + + /* build up an un-decoded filename over successive + filename*= parameters (for use when 2047 decode fails) */ + + mime_fname_rfc2231 = string_sprintf("%#s%s", + mime_fname_rfc2231, q); + + if (!decoding_failed) + { + int size; + if (!mime_filename_charset) + { + uschar * s = q; + + /* look for a ' in the "filename" */ + while(*s != '\'' && *s) s++; /* s is 1st ' or NUL */ + + if ((size = s-q) > 0) + mime_filename_charset = string_copyn(q, size); + + if (*(p = s)) p++; + while(*p == '\'') p++; /* p is after 2nd ' */ + } + else + p = q; + + DEBUG(D_acl) debug_printf_indent("MIME: charset %s fname '%s'\n", + mime_filename_charset ? mime_filename_charset : US"<NULL>", p); + + temp_string = rfc2231_to_2047(p, mime_filename_charset, &slen); + DEBUG(D_acl) debug_printf_indent("MIME: 2047-name %s\n", temp_string); + + temp_string = rfc2047_decode(temp_string, FALSE, NULL, ' ', + NULL, &err_msg); + DEBUG(D_acl) debug_printf_indent("MIME: plain-name %s\n", temp_string); + + if (!temp_string || (size = Ustrlen(temp_string)) == slen) + decoding_failed = TRUE; + else + /* build up a decoded filename over successive + filename*= parameters */ + + mime_filename = mime_fname = mime_fname + ? string_sprintf("%s%s", mime_fname, temp_string) + : temp_string; + } + } + } + + else + /* look for interesting parameters */ + for (mime_parameter * mp = mime_parameter_list; + mp < mime_parameter_list + nelem(mime_parameter_list); + mp++ + ) if (strncmpic(mp->name, p, mp->namelen) == 0) + { + uschar * q; + uschar * dummy_errstr; + + /* grab the value and copy to its expansion variable */ + p += mp->namelen; + q = mime_param_val(&p); /* p now trailing ; or NUL */ + + *mp->value = q && *q + ? rfc2047_decode(q, check_rfc2047_length, NULL, 32, NULL, + &dummy_errstr) + : NULL; + DEBUG(D_acl) debug_printf_indent( + "MIME: found %s parameter in %s header, value '%s'\n", + mp->name, mh->name, *mp->value); + + break; /* done matching param names */ + } + + + /* There is something, but not one of our interesting parameters. + Advance past the next semicolon */ + p = mime_next_semicolon(p); + if (*p) p++; + } /* param scan on line */ + + if (strncmpic(CUS"content-disposition:", header, 20) == 0) + { + if (decoding_failed) mime_filename = mime_fname_rfc2231; + + DEBUG(D_acl) debug_printf_indent( + "MIME: found %s parameter in %s header, value is '%s'\n", + "filename", mh->name, mime_filename); + } + } + } + + /* set additional flag variables (easier access) */ + if ( mime_content_type + && Ustrncmp(mime_content_type,"multipart",9) == 0 + ) + mime_is_multipart = 1; + + /* Make a copy of the boundary pointer. + Required since mime_boundary is global + and can be overwritten further down in recursion */ + nested_context.boundary = mime_boundary; + + /* raise global counter */ + mime_part_count++; + + /* copy current file handle to global variable */ + mime_stream = f; + mime_current_boundary = context ? context->boundary : 0; + + /* Note the context */ + mime_is_coverletter = !(context && context->context == MBC_ATTACHMENT); + + /* call ACL handling function */ + rc = acl_check(ACL_WHERE_MIME, NULL, acl, user_msgptr, log_msgptr); + + mime_stream = NULL; + mime_current_boundary = NULL; + + if (rc != OK) break; + + /* If we have a multipart entity and a boundary, go recursive */ + if ( mime_content_type && nested_context.boundary + && Ustrncmp(mime_content_type,"multipart",9) == 0) + { + DEBUG(D_acl) + debug_printf_indent("MIME: Entering multipart recursion, boundary '%s'\n", + nested_context.boundary); + + nested_context.context = + context && context->context == MBC_ATTACHMENT + ? MBC_ATTACHMENT + : Ustrcmp(mime_content_type,"multipart/alternative") == 0 + || Ustrcmp(mime_content_type,"multipart/related") == 0 + ? MBC_COVERLETTER_ALL + : MBC_COVERLETTER_ONESHOT; + + rc = mime_acl_check(acl, f, &nested_context, user_msgptr, log_msgptr); + if (rc != OK) break; + } + else if ( mime_content_type + && Ustrncmp(mime_content_type,"message/rfc822",14) == 0) + { + const uschar * rfc822name = NULL; + uschar * filename; + int file_nr = 0; + int result = 0; + + /* must find first free sequential filename */ + for (gstring * g = string_get(64); result != -1; g->ptr = 0) + { + struct stat mystat; + g = string_fmt_append(g, + "%s/scan/%s/__rfc822_%05u", spool_directory, message_id, file_nr++); + /* security break */ + if (file_nr >= 128) + goto NO_RFC822; + result = stat(CS (filename = string_from_gstring(g)), &mystat); + } + + rfc822name = filename; + + /* decode RFC822 attachment */ + mime_decoded_filename = NULL; + mime_stream = f; + mime_current_boundary = context ? context->boundary : NULL; + mime_decode(&rfc822name); + mime_stream = NULL; + mime_current_boundary = NULL; + if (!mime_decoded_filename) /* decoding failed */ + { + log_write(0, LOG_MAIN, + "MIME acl condition warning - could not decode RFC822 MIME part to file."); + rc = DEFER; + goto out; + } + mime_decoded_filename = NULL; + } + +NO_RFC822: + /* If the boundary of this instance is NULL, we are finished here */ + if (!context) break; + + if (context->context == MBC_COVERLETTER_ONESHOT) + context->context = MBC_ATTACHMENT; + } + +out: +mime_vars_reset(); +return rc; +} + +#endif /*WITH_CONTENT_SCAN*/ + +/* vi: sw ai sw=2 +*/ |