fusefs: correctly handle servers that report too much data written

During a FUSE_WRITE, the kernel requests the server to write a certain
amount of data, and the server responds with the amount that it actually
did write.  It is obviously an error for the server to write more than
it was provided, and we always treated it as such, but there were two
problems:

* If the server responded with a huge amount, greater than INT_MAX, it
  would trigger an integer overflow which would cause a panic.

* When extending the file, we wrongly set the file's size before
  validing the amount written.

PR:		263263
Reported by:	Robert Morris <rtm@lcs.mit.edu>
MFC after:	2 weeks
Sponsored by:	Axcient
Reviewed by:	emaste
Differential Revision: https://reviews.freebsd.org/D34955

2 files changed, 73 insertions, 6 deletions

diff --git a/sys/fs/fuse/fuse_io.c b/sys/fs/fuse/fuse_io.c
index 07c0f958e028..9ef4badfcdff 100644
--- a/sys/fs/fuse/fuse_io.c
+++ b/sys/fs/fuse/fuse_io.c
@@ -395,8 +395,19 @@ retry:
 
 		fwo = ((struct fuse_write_out *)fdi.answ);
 
+		if (fwo->size > fwi->size) {
+			fuse_warn(data, FSESS_WARN_WROTE_LONG,
+				"wrote more data than we provided it.");
+			/* This is bonkers.  Clear attr cache. */
+			fvdat->flag &= ~FN_SIZECHANGE;
+			fuse_vnode_clear_attr_cache(vp);
+			err = EINVAL;
+			break;
+		}
+
 		/* Adjust the uio in the case of short writes */
 		diff = fwi->size - fwo->size;
+
 		as_written_offset = uio->uio_offset - diff;
 
 		if (as_written_offset - diff > filesize) {
@@ -406,12 +417,7 @@ retry:
 		if (as_written_offset - diff >= filesize)
 			fvdat->flag &= ~FN_SIZECHANGE;
 
-		if (diff < 0) {
-			fuse_warn(data, FSESS_WARN_WROTE_LONG,
-				"wrote more data than we provided it.");
-			err = EINVAL;
-			break;
-		} else if (diff > 0) {
+		if (diff > 0) {
 			/* Short write */
 			if (!direct_io) {
 				fuse_warn(data, FSESS_WARN_SHORT_WRITE,
diff --git a/tests/sys/fs/fusefs/write.cc b/tests/sys/fs/fusefs/write.cc
index db5bb3fe4441..d685bd13aa17 100644
--- a/tests/sys/fs/fusefs/write.cc
+++ b/tests/sys/fs/fusefs/write.cc
@@ -410,6 +410,67 @@ TEST_F(Write, indirect_io_short_write)
 	leak(fd);
 }
 
+/* It is an error if the daemon claims to have written more data than we sent */
+TEST_F(Write, indirect_io_long_write)
+{
+	const char FULLPATH[] = "mountpoint/some_file.txt";
+	const char RELPATH[] = "some_file.txt";
+	const char *CONTENTS = "abcdefghijklmnop";
+	uint64_t ino = 42;
+	int fd;
+	ssize_t bufsize = strlen(CONTENTS);
+	ssize_t bufsize_out = 100;
+	off_t some_other_size = 25;
+	struct stat sb;
+
+	expect_lookup(RELPATH, ino, 0);
+	expect_open(ino, 0, 1);
+	expect_write(ino, 0, bufsize, bufsize_out, CONTENTS);
+	expect_getattr(ino, some_other_size);
+
+	fd = open(FULLPATH, O_WRONLY);
+	ASSERT_LE(0, fd) << strerror(errno);
+
+	ASSERT_EQ(-1, write(fd, CONTENTS, bufsize)) << strerror(errno);
+	ASSERT_EQ(EINVAL, errno);
+
+	/*
+	 * Following such an error, we should requery the server for the file's
+	 * size.
+	 */
+	fstat(fd, &sb);
+	ASSERT_EQ(sb.st_size, some_other_size);
+
+	leak(fd);
+}
+
+/*
+ * Don't crash if the server returns a write that can't be represented as a
+ * signed 32 bit number.  Regression test for
+ * https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=263263
+ */
+TEST_F(Write, indirect_io_very_long_write)
+{
+	const char FULLPATH[] = "mountpoint/some_file.txt";
+	const char RELPATH[] = "some_file.txt";
+	const char *CONTENTS = "abcdefghijklmnop";
+	uint64_t ino = 42;
+	int fd;
+	ssize_t bufsize = strlen(CONTENTS);
+	ssize_t bufsize_out = 3 << 30;
+
+	expect_lookup(RELPATH, ino, 0);
+	expect_open(ino, 0, 1);
+	expect_write(ino, 0, bufsize, bufsize_out, CONTENTS);
+
+	fd = open(FULLPATH, O_WRONLY);
+	ASSERT_LE(0, fd) << strerror(errno);
+
+	ASSERT_EQ(-1, write(fd, CONTENTS, bufsize)) << strerror(errno);
+	ASSERT_EQ(EINVAL, errno);
+	leak(fd);
+}
+
 /* 
  * When the direct_io option is used, filesystems are allowed to write less
  * data than requested.  We should return the short write to userland.