Fix places where a negative return from ftello could be used as invalid input

In a variety of locations in both reading and writing a file, the result
from the C library function ftello is used as input to other functions.  For
the parameters and functions in question, a negative value is invalid input.
This patch checks the return value from the ftello function to determine if
we were able to determine the current position in the file stream and, if not,
fail gracefully.

(issue ASTERISK-19655)
Reported by: Matt Jordan

Review: https://reviewboard.asterisk.org/r/1863/
........

Merged revisions 362355 from http://svn.asterisk.org/svn/asterisk/branches/1.8


git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/10@362356 65c4cc65-6c06-0410-ace0-fbb531ad65f3

funcs/func_env.c

@@ -510,7 +510,11 @@ static int file_read(struct ast_channel *chan, const char *cmd, char *data, stru
 
 		if (offset < 0) {
 			fseeko(ff, offset, SEEK_END);
-			offset = ftello(ff);
+			if ((offset = ftello(ff)) < 0) {
+				ast_log(AST_LOG_ERROR, "Cannot determine offset position of '%s': %s\n", args.filename, strerror(errno));
+				fclose(ff);
+				return -1;
+			}
 		}
 		if (length < 0) {
 			fseeko(ff, length, SEEK_END);
@@ -779,11 +783,15 @@ static int file_write(struct ast_channel *chan, const char *cmd, char *data, con
 
 		if (offset < 0) {
 			if (fseeko(ff, offset, SEEK_END)) {
-				ast_log(LOG_ERROR, "Cannot seek to offset: %s\n", strerror(errno));
+				ast_log(LOG_ERROR, "Cannot seek to offset of '%s': %s\n", args.filename, strerror(errno));
+				fclose(ff);
+				return -1;
+			}
+			if ((offset = ftello(ff)) < 0) {
+				ast_log(AST_LOG_ERROR, "Cannot determine offset position of '%s': %s\n", args.filename, strerror(errno));
 				fclose(ff);
 				return -1;
 			}
-			offset = ftello(ff);
 		}
 
 		if (length < 0) {
@@ -945,10 +953,13 @@ static int file_write(struct ast_channel *chan, const char *cmd, char *data, con
 			} else if (!strchr(args.options, 'd') && fwrite(format2term(newline_format), 1, strlen(format2term(newline_format)), ff) < strlen(format2term(newline_format))) {
 				ast_log(LOG_ERROR, "Short write?!!\n");
 			}
-			truncsize = ftello(ff);
+			if ((truncsize = ftello(ff)) < 0) {
+				ast_log(AST_LOG_ERROR, "Unable to determine truncate position of '%s': %s\n", args.filename, strerror(errno));
+			}
 			fclose(ff);
-			if (truncate(args.filename, truncsize)) {
-				ast_log(LOG_ERROR, "Unable to truncate file: %s\n", strerror(errno));
+			if (truncsize >= 0 && truncate(args.filename, truncsize)) {
+				ast_log(LOG_ERROR, "Unable to truncate file '%s': %s\n", args.filename, strerror(errno));
+				return -1;
 			}
 		} else {
 			int64_t offset_offset = (offset == 0 ? 0 : -1), length_offset = -1, flength, i, current_length = 0;
@@ -970,7 +981,11 @@ static int file_write(struct ast_channel *chan, const char *cmd, char *data, con
 				fclose(ff);
 				return -1;
 			}
-			flength = ftello(ff);
+			if ((flength = ftello(ff)) < 0) {
+				ast_log(AST_LOG_ERROR, "Cannot determine end position of file '%s': %s\n", args.filename, strerror(errno));
+				fclose(ff);
+				return -1;
+			}
 
 			/* For negative offset and/or negative length */
 			if (offset < 0 || length < 0) {
@@ -1115,6 +1130,11 @@ static int file_write(struct ast_channel *chan, const char *cmd, char *data, con
 					return -1;
 				}
 				while ((cur = ftello(ff)) < flength) {
+					if (cur < 0) {
+						ast_log(AST_LOG_ERROR, "Unable to determine last write position for '%s': %s\n", args.filename, strerror(errno));
+						fclose(ff);
+						return -1;
+					}
 					fseeko(ff, length_length - vlen, SEEK_CUR);
 					if (fread(fbuf, 1, sizeof(fbuf), ff) < sizeof(fbuf) && !feof(ff)) {
 						ast_log(LOG_ERROR, "Short read?!!\n");