bug#63832: fix failed inflation of .el.gz archives due to passing empty buffer to inflate()

[Eli Zaretskii]

merge 63832 63831
thanks

> From: Amritpal Singh <icy.amrit@gmail.com>
> Date: Fri, 2 Jun 2023 12:21:07 +0530
> 
> Compile emacs with the system's gzip program set to `pigz`.
> Run emacs and then `M-x eww RET`
> 
> Expected behavior:
> Enter URL prompt in mini-buffer
> 
> Actual behavior:
> hashing failed '/usr/share/emacs/30.0.50/lisp/gnus/gnus.el.gz'
> 
> Report:
> The bug has been reproduced on emacs version 29.0.91 and HEAD which
> seems to be at 30.0.50.
> Later, a copy of the aforementioned file was saved somewhere else and
> the program was uninstalled. Then emacs was recompiled with system's
> gzip program set to GNU gzip and the initial steps were repeated and
> the expected behavior was the result.
> This lead to believing either that there's a bug with how zlib's
> `inflate()` handles archives or emacs code was having an issue with
> archives files.
> 
> The hashes for gz archives generated with different programs were as follows
> > md5sum gnus-gzip.el.gz
> edb3d0ffba7f19ff1d4ec3f889609e8a  gnus-gzip.el.gz
> > md5sum gnus.el.gz
> 985deaaec6a5845ac8d6bd9648957b50  gnus.el.gz
> 
> And when uncompressing these archives, the resulting file was the same
> and the hash for the files was the same (omitted for brevity).
> 
> Now after logging some code in $EMACS_REPO/src/decompress.c, it was
> learned that in the pigz specific case, `inflate()` was returning
> Z_BUF_ERROR(-5) which is an indicator for zstream's either `avail_in`
> or `avail_out` fields are 0.
> 
> Observing the code in `$EMACS_REPO/src/decompress.c`
> L154:
>     } while (!stream.avail_out);
> only checks stream.avail_out and not stream.avail_in which also might
> have been set to 0. A special case here can be constructed where
> `avail_in` is 0, and the code keeps looping even though our input
> buffer is empty and thus causing a Z_BUF_ERROR. Placing a simple check
> for it fixes the bug in pigz's gz archives case and does not cause any
> issue with gzip archives.
> 
> A patch with a simple fix is attached below
> 
> ============================
> 
> >From ffa8e140ed8b093c60f1238bf76935e815e82a21 Mon Sep 17 00:00:00 2001
> From: icebarf <sysgrammer@protonmail.com>
> Date: Fri, 2 Jun 2023 10:51:21 +0530
> Subject: [PATCH] check stream.avail_in as well when looping to inflate gz
>  archive
> 
> ---
>  src/decompress.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/src/decompress.c b/src/decompress.c
> index 6ef17db..162f616 100644
> --- a/src/decompress.c
> +++ b/src/decompress.c
> @@ -151,7 +151,7 @@ md5_gz_stream (FILE *source, void *resblock)
>      return -1;
> 
>        accumulate_and_process_md5 (out, MD5_BLOCKSIZE - stream.avail_out, 
> &ctx);
> -    } while (!stream.avail_out);
> +    } while (stream.avail_in && !stream.avail_out);
> 
>    } while (res != Z_STREAM_END);
> 
> -- 
> 2.40.1
> 
> ==========
> 
> In GNU Emacs 29.0.91 (build 1, x86_64-pc-linux-gnu, GTK+ Version
>  3.24.37, cairo version 1.16.0) of 2023-06-02 built on box
> System Description: KISS Linux
> 
> Configured using:
>  'configure --prefix=/usr --enable-link-time-optimization --with-cairo
>  --with-gnutls --with-imagemagick --with-modules
>  --with-native-compilation --with-pgtk --with-jpeg --with-tiff
>  --with-png --with-rsvg --with-webp --without-dbus --without-lcms2
>  --without-libsystemd --without-gif --without-gconf --without-gsettings
>  --without-m17n-flt --without-selinux --without-x --without-xft
>  --without-xaw3d --without-xim --without-xdbe 'CFLAGS=-O2 -pipe
>  -march=native -mtune=native''

This is a duplicate of bug#63831; merged.