in_tail: avoid double free for multiline msgpack buffer

[hossain-rayhan]

Signed-off-by: Rayhan Hossain hossain.rayhan@outlook.com

We are double freeing &file->mult_sbuf for multiline flush and Fluent Bit is crasing. This happens when we use multiline parser and rotate the file.

The first free is happening at tail_multiline.c:491 and the next free is happening at tail_file.c:1024.

From my investigation, I think we can avoid it in two different ways.

• Assign NULL after freeing the memory at tail_multiline.c:491 which I am doing in this PR. This way we won't have an issue if tail_file.c tries again to free that NULL assigned memory. I tested and it works.
• Rmove the double fee from line tail_file.c:1024. I am not sure if it has any other use case. But this will also work and I have tested it.

Fixes #4177
Copy: aws/aws-for-fluent-bit#255

Fluent Bit is licensed under Apache 2.0, by submitting this pull request I understand that this code will be released under the terms of that license.