Merge branch 'jk/ewah-bounds-check'

The code to read compressed bitmap was not careful to avoid reading
past the end of the file, which has been corrected.

* jk/ewah-bounds-check:
  ewah: adjust callers of ewah_read_mmap()
  ewah_read_mmap: bounds-check mmap reads

5 files changed, 38 insertions, 7 deletions

diff --git a/dir.c b/dir.c
index ccf8b4975e8..fe9bf58e4c7 100644
--- a/dir.c
+++ b/dir.c
@@ -2853,7 +2853,8 @@ struct untracked_cache *read_untracked_extension(const void *data, unsigned long
 	struct read_data rd;
 	const unsigned char *next = data, *end = (const unsigned char *)data + sz;
 	const char *ident;
-	int ident_len, len;
+	int ident_len;
+	ssize_t len;
 	const char *exclude_per_dir;
 
 	if (sz <= 1 || end[-1] != '\0')
diff --git a/ewah/ewah_io.c b/ewah/ewah_io.c
index bed1994551c..33c08c40f89 100644
--- a/ewah/ewah_io.c
+++ b/ewah/ewah_io.c
@@ -122,16 +122,23 @@ int ewah_serialize_strbuf(struct ewah_bitmap *self, struct strbuf *sb)
 	return ewah_serialize_to(self, write_strbuf, sb);
 }
 
-int ewah_read_mmap(struct ewah_bitmap *self, const void *map, size_t len)
+ssize_t ewah_read_mmap(struct ewah_bitmap *self, const void *map, size_t len)
 {
 	const uint8_t *ptr = map;
+	size_t data_len;
 	size_t i;
 
+	if (len < sizeof(uint32_t))
+		return error("corrupt ewah bitmap: eof before bit size");
 	self->bit_size = get_be32(ptr);
 	ptr += sizeof(uint32_t);
+	len -= sizeof(uint32_t);
 
+	if (len < sizeof(uint32_t))
+		return error("corrupt ewah bitmap: eof before length");
 	self->buffer_size = self->alloc_size = get_be32(ptr);
 	ptr += sizeof(uint32_t);
+	len -= sizeof(uint32_t);
 
 	REALLOC_ARRAY(self->buffer, self->alloc_size);
 
@@ -141,15 +148,25 @@ int ewah_read_mmap(struct ewah_bitmap *self, const void *map, size_t len)
 	 * the endianness conversion in a separate pass to ensure
 	 * we're loading 8-byte aligned words.
 	 */
-	memcpy(self->buffer, ptr, self->buffer_size * sizeof(eword_t));
-	ptr += self->buffer_size * sizeof(eword_t);
+	data_len = st_mult(self->buffer_size, sizeof(eword_t));
+	if (len < data_len)
+		return error("corrupt ewah bitmap: eof in data "
+			     "(%"PRIuMAX" bytes short)",
+			     (uintmax_t)(data_len - len));
+	memcpy(self->buffer, ptr, data_len);
+	ptr += data_len;
+	len -= data_len;
 
 	for (i = 0; i < self->buffer_size; ++i)
 		self->buffer[i] = ntohll(self->buffer[i]);
 
+	if (len < sizeof(uint32_t))
+		return error("corrupt ewah bitmap: eof before rlw");
 	self->rlw = self->buffer + get_be32(ptr);
+	ptr += sizeof(uint32_t);
+	len -= sizeof(uint32_t);
 
-	return (3 * 4) + (self->buffer_size * 8);
+	return ptr - (const uint8_t *)map;
 }
 
 int ewah_deserialize(struct ewah_bitmap *self, int fd)
diff --git a/ewah/ewok.h b/ewah/ewok.h
index dc43d05b644..357fd93c84e 100644
--- a/ewah/ewok.h
+++ b/ewah/ewok.h
@@ -91,7 +91,7 @@ int ewah_serialize_native(struct ewah_bitmap *self, int fd);
 int ewah_serialize_strbuf(struct ewah_bitmap *self, struct strbuf *);
 
 int ewah_deserialize(struct ewah_bitmap *self, int fd);
-int ewah_read_mmap(struct ewah_bitmap *self, const void *map, size_t len);
+ssize_t ewah_read_mmap(struct ewah_bitmap *self, const void *map, size_t len);
 
 uint32_t ewah_checksum(struct ewah_bitmap *self);
 
diff --git a/pack-bitmap.c b/pack-bitmap.c
index 06771113fb3..18f8b22aeb4 100644
--- a/pack-bitmap.c
+++ b/pack-bitmap.c
@@ -120,7 +120,7 @@ static struct ewah_bitmap *read_bitmap_1(struct bitmap_index *index)
 {
 	struct ewah_bitmap *b = ewah_pool_new();
 
-	int bitmap_size = ewah_read_mmap(b,
+	ssize_t bitmap_size = ewah_read_mmap(b,
 		index->map + index->map_pos,
 		index->map_size - index->map_pos);
 
diff --git a/t/t5310-pack-bitmaps.sh b/t/t5310-pack-bitmaps.sh
index 423c0a475f7..2d22a17c4a7 100755
--- a/t/t5310-pack-bitmaps.sh
+++ b/t/t5310-pack-bitmaps.sh
@@ -331,4 +331,17 @@ test_expect_success 'pack reuse respects --incremental' '
 	git show-index <empty.idx >actual &&
 	test_cmp expect actual
 '
+
+test_expect_success 'truncated bitmap fails gracefully' '
+	git repack -ad &&
+	git rev-list --use-bitmap-index --count --all >expect &&
+	bitmap=$(ls .git/objects/pack/*.bitmap) &&
+	test_when_finished "rm -f $bitmap" &&
+	head -c 512 <$bitmap >$bitmap.tmp &&
+	mv -f $bitmap.tmp $bitmap &&
+	git rev-list --use-bitmap-index --count --all >actual 2>stderr &&
+	test_cmp expect actual &&
+	test_i18ngrep corrupt stderr
+'
+
 test_done