Re: [PATCH] xz: Apply patch to solve security fix (ZDI-CAN-16587)

["Peter Müller" <peter.mueller@ipfire.org>]

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Reviewed-by: Peter Müller <peter.mueller(a)ipfire.org>

> - Malicious filenames can make xzgrep to write to arbitrary files
>    or (with a GNU sed extension) lead to arbitrary code execution.
> - xzgrep from XZ Utils versions up to and including 5.2.5 are
>    affected. 5.3.1alpha and 5.3.2alpha are affected as well.
> - This bug was inherited from gzip's zgrep. gzip 1.12 includes
>    a fix for zgrep.
> - CU167 has gzip-1.12 with the fix already merged.
> 
> Signed-off-by: Adolf Belka <adolf.belka(a)ipfire.org>
> ---
>  lfs/xz                                 |  1 +
>  src/patches/xzgrep-ZDI-CAN-16587.patch | 94 ++++++++++++++++++++++++++
>  2 files changed, 95 insertions(+)
>  create mode 100644 src/patches/xzgrep-ZDI-CAN-16587.patch
> 
> diff --git a/lfs/xz b/lfs/xz
> index 586fbc90f..9345df954 100644
> --- a/lfs/xz
> +++ b/lfs/xz
> @@ -75,6 +75,7 @@ $(subst %,%_BLAKE2,$(objects)) :
>  $(TARGET) : $(patsubst %,$(DIR_DL)/%,$(objects))
>  	@$(PREBUILD)
>  	@rm -rf $(DIR_APP) && cd $(DIR_SRC) && tar axf $(DIR_DL)/$(DL_FILE)
> +	cd $(DIR_APP) && patch -p1 -i $(DIR_SRC)/src/patches/xzgrep-ZDI-CAN-16587.patch
>  	cd $(DIR_APP) && ./configure --prefix=$(PREFIX)
>  	cd $(DIR_APP) && make $(MAKETUNING)
>  	cd $(DIR_APP) && make install
> diff --git a/src/patches/xzgrep-ZDI-CAN-16587.patch b/src/patches/xzgrep-ZDI-CAN-16587.patch
> new file mode 100644
> index 000000000..406ded590
> --- /dev/null
> +++ b/src/patches/xzgrep-ZDI-CAN-16587.patch
> @@ -0,0 +1,94 @@
> +From 69d1b3fc29677af8ade8dc15dba83f0589cb63d6 Mon Sep 17 00:00:00 2001
> +From: Lasse Collin <lasse.collin(a)tukaani.org>
> +Date: Tue, 29 Mar 2022 19:19:12 +0300
> +Subject: [PATCH] xzgrep: Fix escaping of malicious filenames (ZDI-CAN-16587).
> +
> +Malicious filenames can make xzgrep to write to arbitrary files
> +or (with a GNU sed extension) lead to arbitrary code execution.
> +
> +xzgrep from XZ Utils versions up to and including 5.2.5 are
> +affected. 5.3.1alpha and 5.3.2alpha are affected as well.
> +This patch works for all of them.
> +
> +This bug was inherited from gzip's zgrep. gzip 1.12 includes
> +a fix for zgrep.
> +
> +The issue with the old sed script is that with multiple newlines,
> +the N-command will read the second line of input, then the
> +s-commands will be skipped because it's not the end of the
> +file yet, then a new sed cycle starts and the pattern space
> +is printed and emptied. So only the last line or two get escaped.
> +
> +One way to fix this would be to read all lines into the pattern
> +space first. However, the included fix is even simpler: All lines
> +except the last line get a backslash appended at the end. To ensure
> +that shell command substitution doesn't eat a possible trailing
> +newline, a colon is appended to the filename before escaping.
> +The colon is later used to separate the filename from the grep
> +output so it is fine to add it here instead of a few lines later.
> +
> +The old code also wasn't POSIX compliant as it used \n in the
> +replacement section of the s-command. Using \<newline> is the
> +POSIX compatible method.
> +
> +LC_ALL=C was added to the two critical sed commands. POSIX sed
> +manual recommends it when using sed to manipulate pathnames
> +because in other locales invalid multibyte sequences might
> +cause issues with some sed implementations. In case of GNU sed,
> +these particular sed scripts wouldn't have such problems but some
> +other scripts could have, see:
> +
> +    info '(sed)Locale Considerations'
> +
> +This vulnerability was discovered by:
> +cleemy desu wayo working with Trend Micro Zero Day Initiative
> +
> +Thanks to Jim Meyering and Paul Eggert discussing the different
> +ways to fix this and for coordinating the patch release schedule
> +with gzip.
> +---
> + src/scripts/xzgrep.in | 20 ++++++++++++--------
> + 1 file changed, 12 insertions(+), 8 deletions(-)
> +
> +diff --git a/src/scripts/xzgrep.in b/src/scripts/xzgrep.in
> +index b180936..e5186ba 100644
> +--- a/src/scripts/xzgrep.in
> ++++ b/src/scripts/xzgrep.in
> +@@ -180,22 +180,26 @@ for i; do
> +          { test $# -eq 1 || test $no_filename -eq 1; }; then
> +       eval "$grep"
> +     else
> ++      # Append a colon so that the last character will never be a newline
> ++      # which would otherwise get lost in shell command substitution.
> ++      i="$i:"
> ++
> ++      # Escape & \ | and newlines only if such characters are present
> ++      # (speed optimization).
> +       case $i in
> +       (*'
> + '* | *'&'* | *'\'* | *'|'*)
> +-        i=$(printf '%s\n' "$i" |
> +-            sed '
> +-              $!N
> +-              $s/[&\|]/\\&/g
> +-              $s/\n/\\n/g
> +-            ');;
> ++        i=$(printf '%s\n' "$i" | LC_ALL=C sed 's/[&\|]/\\&/g; $!s/$/\\/');;
> +       esac
> +-      sed_script="s|^|$i:|"
> ++
> ++      # $i already ends with a colon so don't add it here.
> ++      sed_script="s|^|$i|"
> + 
> +       # Fail if grep or sed fails.
> +       r=$(
> +         exec 4>&1
> +-        (eval "$grep" 4>&-; echo $? >&4) 3>&- | sed "$sed_script" >&3 4>&-
> ++        (eval "$grep" 4>&-; echo $? >&4) 3>&- |
> ++            LC_ALL=C sed "$sed_script" >&3 4>&-
> +       ) || r=2
> +       exit $r
> +     fi >&3 5>&-
> +-- 
> +2.35.1
> +