[PATCH] erofs-utils: fuse: fix random readlink error

[Hu Weiwen]

readlink should fill a **null terminated** string in buffer.

Also, read should return number of bytes remaining on EOF.

Link: https://lore.kernel.org/linux-erofs/20210121101233.GC6680@DESKTOP-N4CECTO.huww98.cn/
Signed-off-by: Hu Weiwen <sehuww at mail.scut.edu.cn>
---
 fuse/main.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/fuse/main.c b/fuse/main.c
index c162912..bc1e496 100644
--- a/fuse/main.c
+++ b/fuse/main.c
@@ -71,6 +71,12 @@ static int erofsfuse_read(const char *path, char *buffer,
 	if (ret)
 		return ret;
 
+	if (offset >= vi.i_size)
+		return 0;
+
+	if (offset + size > vi.i_size)
+		size = vi.i_size - offset;
+
 	ret = erofs_pread(&vi, buffer, size, offset);
 	if (ret)
 		return ret;
@@ -79,10 +85,16 @@ static int erofsfuse_read(const char *path, char *buffer,
 
 static int erofsfuse_readlink(const char *path, char *buffer, size_t size)
 {
-	int ret = erofsfuse_read(path, buffer, size, 0, NULL);
+	int ret;
+	size_t path_len;
+
+	erofs_dbg("path:%s size=%zd", path, size);
+	ret = erofsfuse_read(path, buffer, size, 0, NULL);
 
 	if (ret < 0)
 		return ret;
+	path_len = min(size - 1, (size_t)ret);
+	buffer[path_len] = '\0';
 	return 0;
 }
 
-- 
2.30.0