vcs-svn: avoid hangs from corrupt deltas

A corrupt Subversion-format delta can request reads past the end of
the preimage.  Set sliding_view::max_off so such corruption is caught
when it appears rather than blocking in an impossible-to-fulfill
read() when input is coming from a socket or pipe.

Inspired-by: Ramkumar Ramachandra <artagnon@gmail.com>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>

Author: jrn

t/t9010-svn-fe.sh

@@ -18,12 +18,13 @@ reinit_git () {
 
 try_dump () {
 	input=$1 &&
-	maybe_fail=${2:+test_$2} &&
+	maybe_fail_svnfe=${2:+test_$2} &&
+	maybe_fail_fi=${3:+test_$3} &&
 
 	{
-		$maybe_fail test-svn-fe "$input" >stream 3<backflow &
+		$maybe_fail_svnfe test-svn-fe "$input" >stream 3<backflow &
 	} &&
-	git fast-import --cat-blob-fd=3 <stream 3>backflow &&
+	$maybe_fail_fi git fast-import --cat-blob-fd=3 <stream 3>backflow &&
 	wait $!
 }
 
@@ -1047,6 +1048,39 @@ test_expect_success PIPE 'deltas need not consume the whole preimage' '
 	test_cmp expect.3 actual.3
 '
 
+test_expect_success PIPE 'no hang for delta trying to read past end of preimage' '
+	reinit_git &&
+	{
+		# COPY 1
+		printf "SVNQ%b%b" "Q\001\001\002Q" "\001Q" |
+		q_to_nul
+	} >greedy.delta &&
+	{
+		cat <<-\EOF &&
+		SVN-fs-dump-format-version: 3
+
+		Revision-number: 1
+		Prop-content-length: 10
+		Content-length: 10
+
+		PROPS-END
+
+		Node-path: bootstrap
+		Node-kind: file
+		Node-action: add
+		Text-delta: true
+		Prop-content-length: 10
+		EOF
+		echo Text-content-length: $(wc -c <greedy.delta) &&
+		echo Content-length: $((10 + $(wc -c <greedy.delta))) &&
+		echo &&
+		echo PROPS-END &&
+		cat greedy.delta &&
+		echo
+	} >greedydelta.dump &&
+	try_dump greedydelta.dump must_fail might_fail
+'
+
 test_expect_success 'set up svn repo' '
 	svnconf=$PWD/svnconf &&
 	mkdir -p "$svnconf" &&

vcs-svn/fast_export.c

@@ -198,8 +198,7 @@ static long apply_delta(off_t len, struct line_buffer *input,
 			const char *old_data, uint32_t old_mode)
 {
 	long ret;
-	off_t preimage_len = 0;
-	struct sliding_view preimage = SLIDING_VIEW_INIT(&report_buffer, -1);
+	struct sliding_view preimage = SLIDING_VIEW_INIT(&report_buffer, 0);
 	FILE *out;
 
 	if (init_postimage() || !(out = buffer_tmpfile_rewind(&postimage)))
@@ -211,19 +210,23 @@ static long apply_delta(off_t len, struct line_buffer *input,
 		printf("cat-blob %s\n", old_data);
 		fflush(stdout);
 		response = get_response_line();
-		if (parse_cat_response_line(response, &preimage_len))
+		if (parse_cat_response_line(response, &preimage.max_off))
 			die("invalid cat-blob response: %s", response);
+		check_preimage_overflow(preimage.max_off, 1);
 	}
 	if (old_mode == REPO_MODE_LNK) {
 		strbuf_addstr(&preimage.buf, "link ");
-		check_preimage_overflow(preimage_len, strlen("link "));
-		preimage_len += strlen("link ");
+		check_preimage_overflow(preimage.max_off, strlen("link "));
+		preimage.max_off += strlen("link ");
+		check_preimage_overflow(preimage.max_off, 1);
 	}
 	if (svndiff0_apply(input, len, &preimage, out))
 		die("cannot apply delta");
 	if (old_data) {
 		/* Read the remainder of preimage and trailing newline. */
-		if (move_window(&preimage, preimage_len, 1))
+		assert(!signed_add_overflows(preimage.max_off, 1));
+		preimage.max_off++;	/* room for newline */
+		if (move_window(&preimage, preimage.max_off - 1, 1))
 			die("cannot seek to end of input");
 		if (preimage.buf.buf[0] != '\n')
 			die("missing newline after cat-blob response");