fusefs: fix a buffer overflow in the tests

The actual overflow occured in the ReadAhead.readahead test.
Surprisingly it has never segfaulted or resulted in any bad behavior.

MFC after:	1 week
Sponsored by:	Axcient
Reviewed by:	emaste
Differential Revision: https://reviews.freebsd.org/D38718

tests/sys/fs/fusefs/bmap.cc

@@ -210,6 +210,8 @@ TEST_P(BmapEof, eof)
 		_)
 	).WillOnce(Invoke(ReturnImmediate([=](auto in, auto& out) {
 		size_t osize = in.body.read.size;
+
+		assert(osize < sizeof(out.body.bytes));
 		out.header.len = sizeof(struct fuse_out_header) + osize;
 		bzero(out.body.bytes, osize);
 	})));

tests/sys/fs/fusefs/fallocate.cc

@@ -70,6 +70,7 @@ void expect_vop_stddeallocate(uint64_t ino, uint64_t off, uint64_t length)
 		}, Eq(true)),
 		_)
 	).WillOnce(Invoke(ReturnImmediate([=](auto in, auto& out) {
+		assert(in.body.read.size <= sizeof(out.body.bytes));
 		out.header.len = sizeof(struct fuse_out_header) +
 			in.body.read.size;
 		memset(out.body.bytes, 'X', in.body.read.size);
@@ -79,6 +80,8 @@ void expect_vop_stddeallocate(uint64_t ino, uint64_t off, uint64_t length)
 			const char *buf = (const char*)in.body.bytes +
 				sizeof(struct fuse_write_in);
 
+			assert(length <= sizeof(in.body.bytes) -
+				sizeof(struct fuse_write_in));
 			return (in.header.opcode == FUSE_WRITE &&
 				in.header.nodeid == ino &&
 				in.body.write.offset == off  &&

tests/sys/fs/fusefs/io.cc

@@ -141,6 +141,8 @@ void SetUp()
 		ssize_t isize = in.body.write.size;
 		off_t iofs = in.body.write.offset;
 
+		assert((size_t)isize <= sizeof(in.body.bytes) -
+			sizeof(struct fuse_write_in));
 		ASSERT_EQ(isize, pwrite(m_backing_fd, buf, isize, iofs))
 			<< strerror(errno);
 		SET_OUT_HEADER_LEN(out, write);
@@ -158,6 +160,7 @@ void SetUp()
 		void *buf = out.body.bytes;
 		ssize_t osize;
 
+		assert((size_t)isize <= sizeof(out.body.bytes));
 		osize = pread(m_backing_fd, buf, isize, iofs);
 		ASSERT_LE(0, osize) << strerror(errno);
 		out.header.len = sizeof(struct fuse_out_header) + osize;

tests/sys/fs/fusefs/mockfs.hh

@@ -206,7 +206,7 @@ union fuse_payloads_out {
 	 * The protocol places no limits on the size of bytes.  Choose
 	 * a size big enough for anything we'll test.
 	 */
-	uint8_t			bytes[0x20000];
+	uint8_t			bytes[0x40000];
 	fuse_entry_out		entry;
 	fuse_entry_out_7_8	entry_7_8;
 	fuse_lk_out		getlk;

tests/sys/fs/fusefs/setattr.cc

@@ -530,6 +530,7 @@ TEST_F(Setattr, truncate_discards_cached_data) {
 		auto osize = std::min(
 			static_cast<uint64_t>(cur_size) - in.body.read.offset,
 			static_cast<uint64_t>(in.body.read.size));
+		assert(osize <= sizeof(out.body.bytes));
 		out.header.len = sizeof(struct fuse_out_header) + osize;
 		if (should_have_data)
 			memset(out.body.bytes, 'X', osize);

tests/sys/fs/fusefs/utils.cc

@@ -400,6 +400,7 @@ void FuseTest::expect_read(uint64_t ino, uint64_t offset, uint64_t isize,
 		}, Eq(true)),
 		_)
 	).WillOnce(Invoke(ReturnImmediate([=](auto in __unused, auto& out) {
+		assert(osize <= sizeof(out.body.bytes));
 		out.header.len = sizeof(struct fuse_out_header) + osize;
 		memmove(out.body.bytes, contents, osize);
 	}))).RetiresOnSaturation();
@@ -502,6 +503,8 @@ void FuseTest::expect_write(uint64_t ino, uint64_t offset, uint64_t isize,
 			bool pid_ok;
 			uint32_t wf = in.body.write.write_flags;
 
+			assert(isize <= sizeof(in.body.bytes) -
+				sizeof(struct fuse_write_in));
 			if (wf & FUSE_WRITE_CACHE)
 				pid_ok = true;
 			else
@@ -534,6 +537,9 @@ void FuseTest::expect_write_7_8(uint64_t ino, uint64_t offset, uint64_t isize,
 			const char *buf = (const char*)in.body.bytes +
 				FUSE_COMPAT_WRITE_IN_SIZE;
 			bool pid_ok = (pid_t)in.header.pid == getpid();
+
+			assert(isize <= sizeof(in.body.bytes) -
+				FUSE_COMPAT_WRITE_IN_SIZE);
 			return (in.header.opcode == FUSE_WRITE &&
 				in.header.nodeid == ino &&
 				in.body.write.fh == FH &&

tests/sys/fs/fusefs/write.cc

@@ -97,6 +97,8 @@ void maybe_expect_write(uint64_t ino, uint64_t offset, uint64_t size,
 			const char *buf = (const char*)in.body.bytes +
 				sizeof(struct fuse_write_in);
 
+			assert(size <= sizeof(in.body.bytes) -
+				sizeof(struct fuse_write_in));
 			return (in.header.opcode == FUSE_WRITE &&
 				in.header.nodeid == ino &&
 				in.body.write.offset == offset  &&