Commit message: Fix bug #77950 - Heap-buffer-overflow in _estrndup via exif_process_IFD_TAG

I do not completely understand what is going on there, but I am pretty
sure dir_entry <= offset_base if not a normal situation, so we better not
to rely on such dir_entry.
CVE: CVE-2019-11036
CWE: CWE-125
Vulnerability description: When processing certain files, PHP EXIF extension in versions 7.1.x below 7.1.29, 7.2.x below 7.2.18 and 7.3.x below 7.3.5 can be caused to read past allocated buffer in exif_process_IFD_TAG function. This may lead to information disclosure or crash.

Project: php-src

static int exif_process_IFD_TAG(image_info_type *ImageInfo, char *dir_entry, char *offset_base, size_t IFDlength, size_t displacement, int section_index, int ReadNextIFD, tag_table_type tag_table)
{
	size_t length;
	unsigned int tag, format, components;
	char *value_ptr, tagname[64], cbuf[32], *outside=NULL;
	size_t byte_count, offset_val, fpos, fgot;
	int64_t byte_count_signed;
	xp_field_type *tmp_xp;
#ifdef EXIF_DEBUG
	char *dump_data;
	int dump_free;
#endif /* EXIF_DEBUG */

	/* Protect against corrupt headers */
	if (ImageInfo->ifd_nesting_level > MAX_IFD_NESTING_LEVEL) {
		exif_error_docref("exif_read_data#error_ifd" EXIFERR_CC, ImageInfo, E_WARNING, "corrupt EXIF header: maximum directory nesting level reached");
		return FALSE;
	}
	ImageInfo->ifd_nesting_level++;

	tag = php_ifd_get16u(dir_entry, ImageInfo->motorola_intel);
	format = php_ifd_get16u(dir_entry+2, ImageInfo->motorola_intel);
	components = php_ifd_get32u(dir_entry+4, ImageInfo->motorola_intel);

	if (!format || format > NUM_FORMATS) {
		/* (-1) catches illegal zero case as unsigned underflows to positive large. */
		exif_error_docref("exif_read_data#error_ifd" EXIFERR_CC, ImageInfo, E_WARNING, "Process tag(x%04X=%s): Illegal format code 0x%04X, suppose BYTE", tag, exif_get_tagname(tag, tagname, -12, tag_table), format);
		format = TAG_FMT_BYTE;
		/*return TRUE;*/
	}

	if (components < 0) {
		exif_error_docref("exif_read_data#error_ifd" EXIFERR_CC, ImageInfo, E_WARNING, "Process tag(x%04X=%s): Illegal components(%d)", tag, exif_get_tagname(tag, tagname, -12, tag_table), components);
		return FALSE;
	}

	byte_count_signed = (int64_t)components * php_tiff_bytes_per_format[format];

	if (byte_count_signed < 0 || (byte_count_signed > INT32_MAX)) {
		exif_error_docref("exif_read_data#error_ifd" EXIFERR_CC, ImageInfo, E_WARNING, "Process tag(x%04X=%s): Illegal byte_count", tag, exif_get_tagname(tag, tagname, -12, tag_table));
		return FALSE;
	}

	byte_count = (size_t)byte_count_signed;

	if (byte_count > 4) {
		offset_val = php_ifd_get32u(dir_entry+8, ImageInfo->motorola_intel);
		/* If its bigger than 4 bytes, the dir entry contains an offset. */
		value_ptr = offset_base+offset_val;
        /*
            dir_entry is ImageInfo->file.list[sn].data+2+i*12
            offset_base is ImageInfo->file.list[sn].data-dir_offset
            dir_entry - offset_base is dir_offset+2+i*12
        */
		if (byte_count > IFDlength || offset_val > IFDlength-byte_count || value_ptr < dir_entry || offset_val < (size_t)(dir_entry-offset_base)) {
			/* It is important to check for IMAGE_FILETYPE_TIFF
			 * JPEG does not use absolute pointers instead its pointers are
			 * relative to the start of the TIFF header in APP1 section. */
			if (byte_count > ImageInfo->FileSize || offset_val>ImageInfo->FileSize-byte_count || (ImageInfo->FileType!=IMAGE_FILETYPE_TIFF_II && ImageInfo->FileType!=IMAGE_FILETYPE_TIFF_MM && ImageInfo->FileType!=IMAGE_FILETYPE_JPEG)) {
				if (value_ptr < dir_entry) {
					/* we can read this if offset_val > 0 */
					/* some files have their values in other parts of the file */
					exif_error_docref("exif_read_data#error_ifd" EXIFERR_CC, ImageInfo, E_WARNING, "Process tag(x%04X=%s): Illegal pointer offset(x%04X < x%04X)", tag, exif_get_tagname(tag, tagname, -12, tag_table), offset_val, dir_entry);
				} else {
					/* this is for sure not allowed */
					/* exception are IFD pointers */
					exif_error_docref("exif_read_data#error_ifd" EXIFERR_CC, ImageInfo, E_WARNING, "Process tag(x%04X=%s): Illegal pointer offset(x%04X + x%04X = x%04X > x%04X)", tag, exif_get_tagname(tag, tagname, -12, tag_table), offset_val, byte_count, offset_val+byte_count, IFDlength);
				}
				return FALSE;
			}
			if (byte_count>sizeof(cbuf)) {
				/* mark as outside range and get buffer */
				value_ptr = safe_emalloc(byte_count, 1, 0);
				outside = value_ptr;
			} else {
				/* In most cases we only access a small range so
				 * it is faster to use a static buffer there
				 * BUT it offers also the possibility to have
				 * pointers read without the need to free them
				 * explicitley before returning. */
				memset(&cbuf, 0, sizeof(cbuf));
				value_ptr = cbuf;
			}

			fpos = php_stream_tell(ImageInfo->infile);
			php_stream_seek(ImageInfo->infile, displacement+offset_val, SEEK_SET);
			fgot = php_stream_tell(ImageInfo->infile);
			if (fgot!=displacement+offset_val) {
				EFREE_IF(outside);
				exif_error_docref(NULL EXIFERR_CC, ImageInfo, E_WARNING, "Wrong file pointer: 0x%08X != 0x%08X", fgot, displacement+offset_val);
				return FALSE;
			}
			fgot = php_stream_read(ImageInfo->infile, value_ptr, byte_count);
			php_stream_seek(ImageInfo->infile, fpos, SEEK_SET);
			if (fgot<byte_count) {
				EFREE_IF(outside);
				EXIF_ERRLOG_FILEEOF(ImageInfo)
				return FALSE;
			}
		}
	} else {
		/* 4 bytes or less and value is in the dir entry itself */
		value_ptr = dir_entry+8;
		offset_val= value_ptr-offset_base;
	}

	ImageInfo->sections_found |= FOUND_ANY_TAG;
#ifdef EXIF_DEBUG
	dump_data = exif_dump_data(&dump_free, format, components, length, ImageInfo->motorola_intel, value_ptr);
	exif_error_docref(NULL EXIFERR_CC, ImageInfo, E_NOTICE, "Process tag(x%04X=%s,@x%04X + x%04X(=%d)): %s%s %s", tag, exif_get_tagname(tag, tagname, -12, tag_table), offset_val+displacement, byte_count, byte_count, (components>1)&&format!=TAG_FMT_UNDEFINED&&format!=TAG_FMT_STRING?"ARRAY OF ":"", exif_get_tagformat(format), dump_data);
	if (dump_free) {
		efree(dump_data);
	}
#endif

	if (section_index==SECTION_THUMBNAIL) {
		if (!ImageInfo->Thumbnail.data) {
			switch(tag) {
				case TAG_IMAGEWIDTH:
				case TAG_COMP_IMAGE_WIDTH:
					ImageInfo->Thumbnail.width = exif_convert_any_to_int(value_ptr, format, ImageInfo->motorola_intel);
					break;

				case TAG_IMAGEHEIGHT:
				case TAG_COMP_IMAGE_HEIGHT:
					ImageInfo->Thumbnail.height = exif_convert_any_to_int(value_ptr, format, ImageInfo->motorola_intel);
					break;

				case TAG_STRIP_OFFSETS:
				case TAG_JPEG_INTERCHANGE_FORMAT:
					/* accept both formats */
					ImageInfo->Thumbnail.offset = exif_convert_any_to_int(value_ptr, format, ImageInfo->motorola_intel);
					break;

				case TAG_STRIP_BYTE_COUNTS:
					if (ImageInfo->FileType == IMAGE_FILETYPE_TIFF_II || ImageInfo->FileType == IMAGE_FILETYPE_TIFF_MM) {
						ImageInfo->Thumbnail.filetype = ImageInfo->FileType;
					} else {
						/* motorola is easier to read */
						ImageInfo->Thumbnail.filetype = IMAGE_FILETYPE_TIFF_MM;
					}
					ImageInfo->Thumbnail.size = exif_convert_any_to_int(value_ptr, format, ImageInfo->motorola_intel);
					break;

				case TAG_JPEG_INTERCHANGE_FORMAT_LEN:
					if (ImageInfo->Thumbnail.filetype == IMAGE_FILETYPE_UNKNOWN) {
						ImageInfo->Thumbnail.filetype = IMAGE_FILETYPE_JPEG;
						ImageInfo->Thumbnail.size = exif_convert_any_to_int(value_ptr, format, ImageInfo->motorola_intel);
					}
					break;
			}
		}
	} else {
		if (section_index==SECTION_IFD0 || section_index==SECTION_EXIF)
		switch(tag) {
			case TAG_COPYRIGHT:
				/* check for "<photographer> NUL <editor> NUL" */
				if (byte_count>1 && (length=php_strnlen(value_ptr, byte_count)) > 0) {
					if (length<byte_count-1) {
						/* When there are any characters after the first NUL */
						ImageInfo->CopyrightPhotographer  = estrdup(value_ptr);
						ImageInfo->CopyrightEditor        = estrndup(value_ptr+length+1, byte_count-length-1);
						spprintf(&ImageInfo->Copyright, 0, "%s, %s", ImageInfo->CopyrightPhotographer, ImageInfo->CopyrightEditor);
						/* format = TAG_FMT_UNDEFINED; this musn't be ASCII         */
						/* but we are not supposed to change this                   */
						/* keep in mind that image_info does not store editor value */
					} else {
						ImageInfo->Copyright = estrndup(value_ptr, byte_count);
					}
				}
				break;

			case TAG_USERCOMMENT:
				ImageInfo->UserCommentLength = exif_process_user_comment(ImageInfo, &(ImageInfo->UserComment), &(ImageInfo->UserCommentEncoding), value_ptr, byte_count);
				break;

			case TAG_XP_TITLE:
			case TAG_XP_COMMENTS:
			case TAG_XP_AUTHOR:
			case TAG_XP_KEYWORDS:
			case TAG_XP_SUBJECT:
				tmp_xp = (xp_field_type*)safe_erealloc(ImageInfo->xp_fields.list, (ImageInfo->xp_fields.count+1), sizeof(xp_field_type), 0);
				ImageInfo->sections_found |= FOUND_WINXP;
				ImageInfo->xp_fields.list = tmp_xp;
				ImageInfo->xp_fields.count++;
				exif_process_unicode(ImageInfo, &(ImageInfo->xp_fields.list[ImageInfo->xp_fields.count-1]), tag, value_ptr, byte_count);
				break;

			case TAG_FNUMBER:
				/* Simplest way of expressing aperture, so I trust it the most.
				   (overwrite previously computed value if there is one) */
				ImageInfo->ApertureFNumber = (float)exif_convert_any_format(value_ptr, format, ImageInfo->motorola_intel);
				break;

			case TAG_APERTURE:
			case TAG_MAX_APERTURE:
				/* More relevant info always comes earlier, so only use this field if we don't
				   have appropriate aperture information yet. */
				if (ImageInfo->ApertureFNumber == 0) {
					ImageInfo->ApertureFNumber
						= (float)exp(exif_convert_any_format(value_ptr, format, ImageInfo->motorola_intel)*log(2)*0.5);
				}
				break;

			case TAG_SHUTTERSPEED:
				/* More complicated way of expressing exposure time, so only use
				   this value if we don't already have it from somewhere else.
				   SHUTTERSPEED comes after EXPOSURE TIME
				  */
				if (ImageInfo->ExposureTime == 0) {
					ImageInfo->ExposureTime
						= (float)(1/exp(exif_convert_any_format(value_ptr, format, ImageInfo->motorola_intel)*log(2)));
				}
				break;
			case TAG_EXPOSURETIME:
				ImageInfo->ExposureTime = -1;
				break;

			case TAG_COMP_IMAGE_WIDTH:
				ImageInfo->ExifImageWidth = exif_convert_any_to_int(value_ptr, format, ImageInfo->motorola_intel);
				break;

			case TAG_FOCALPLANE_X_RES:
				ImageInfo->FocalplaneXRes = exif_convert_any_format(value_ptr, format, ImageInfo->motorola_intel);
				break;

			case TAG_SUBJECT_DISTANCE:
				/* Inidcates the distacne the autofocus camera is focused to.
				   Tends to be less accurate as distance increases. */
				ImageInfo->Distance = (float)exif_convert_any_format(value_ptr, format, ImageInfo->motorola_intel);
				break;

			case TAG_FOCALPLANE_RESOLUTION_UNIT:
				switch((int)exif_convert_any_format(value_ptr, format, ImageInfo->motorola_intel)) {
					case 1: ImageInfo->FocalplaneUnits = 25.4; break; /* inch */
					case 2:
						/* According to the information I was using, 2 measn meters.
						   But looking at the Cannon powershot's files, inches is the only
						   sensible value. */
						ImageInfo->FocalplaneUnits = 25.4;
						break;

					case 3: ImageInfo->FocalplaneUnits = 10;   break;  /* centimeter */
					case 4: ImageInfo->FocalplaneUnits = 1;    break;  /* milimeter  */
					case 5: ImageInfo->FocalplaneUnits = .001; break;  /* micrometer */
				}
				break;

			case TAG_SUB_IFD:
				if (format==TAG_FMT_IFD) {
					/* If this is called we are either in a TIFFs thumbnail or a JPEG where we cannot handle it */
					/* TIFF thumbnail: our data structure cannot store a thumbnail of a thumbnail */
					/* JPEG do we have the data area and what to do with it */
					exif_error_docref(NULL EXIFERR_CC, ImageInfo, E_NOTICE, "Skip SUB IFD");
				}
				break;

			case TAG_MAKE:
				ImageInfo->make = estrndup(value_ptr, byte_count);
				break;
			case TAG_MODEL:
				ImageInfo->model = estrndup(value_ptr, byte_count);
				break;

			case TAG_MAKER_NOTE:
				if (!exif_process_IFD_in_MAKERNOTE(ImageInfo, value_ptr, byte_count, offset_base, IFDlength, displacement)) {
					EFREE_IF(outside);
					return FALSE;
				}
				break;

			case TAG_EXIF_IFD_POINTER:
			case TAG_GPS_IFD_POINTER:
			case TAG_INTEROP_IFD_POINTER:
				if (ReadNextIFD) {
					char *Subdir_start;
					int sub_section_index = 0;
					switch(tag) {
						case TAG_EXIF_IFD_POINTER:
#ifdef EXIF_DEBUG
							exif_error_docref(NULL EXIFERR_CC, ImageInfo, E_NOTICE, "Found EXIF");
#endif
							ImageInfo->sections_found |= FOUND_EXIF;
							sub_section_index = SECTION_EXIF;
							break;
						case TAG_GPS_IFD_POINTER:
#ifdef EXIF_DEBUG
							exif_error_docref(NULL EXIFERR_CC, ImageInfo, E_NOTICE, "Found GPS");
#endif
							ImageInfo->sections_found |= FOUND_GPS;
							sub_section_index = SECTION_GPS;
							break;
						case TAG_INTEROP_IFD_POINTER:
#ifdef EXIF_DEBUG
							exif_error_docref(NULL EXIFERR_CC, ImageInfo, E_NOTICE, "Found INTEROPERABILITY");
#endif
							ImageInfo->sections_found |= FOUND_INTEROP;
							sub_section_index = SECTION_INTEROP;
							break;
					}
					Subdir_start = offset_base + php_ifd_get32u(value_ptr, ImageInfo->motorola_intel);
					if (Subdir_start < offset_base || Subdir_start > offset_base+IFDlength) {
						exif_error_docref("exif_read_data#error_ifd" EXIFERR_CC, ImageInfo, E_WARNING, "Illegal IFD Pointer");
						return FALSE;
					}
					if (!exif_process_IFD_in_JPEG(ImageInfo, Subdir_start, offset_base, IFDlength, displacement, sub_section_index)) {
						return FALSE;
					}
#ifdef EXIF_DEBUG
					exif_error_docref(NULL EXIFERR_CC, ImageInfo, E_NOTICE, "Subsection %s done", exif_get_sectionname(sub_section_index));
#endif
				}
		}
	}
	exif_iif_add_tag(ImageInfo, section_index, exif_get_tagname(tag, tagname, sizeof(tagname), tag_table), tag, format, components, value_ptr, byte_count);
	EFREE_IF(outside);
	return TRUE;
}