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fix: apply workaround patch for vcs_info (CVE-2021-45444)

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This lib function applies a patch to the VCS_INFO_formats function
in zsh versions from v5.0.3 until v5.8, which don't quote % chars
in some arguments received. Normally that just means that some
% characters in these strings (branch names, directories, etc.)
will be incorrectly parsed as formatting sequences.

With CVE-2021-45444, however, this means that one of these strings
from a malicious source (e.g. a malicious git repository) can
trigger command injection and run arbitrary code in the user's
machine when visiting such git repository.

Zsh 5.8.1 fixes this vulnerability [1], but older vcs_info setups
still need a workaround such as this one to patch the vulnerability.

[1] c3ea1e5d52
This commit is contained in:
Marc Cornellà 2022-02-13 18:59:27 +01:00
parent 02b52a03a5
commit ef3f7c43a9
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# Impacted versions go from v5.0.3 to v5.8 (v5.8.1 is the first patched version)
autoload -Uz is-at-least
if is-at-least 5.8.1 || ! is-at-least 5.0.3; then
return
fi
# Quote necessary $hook_com[<field>] items just before they are used
# in the line "VCS_INFO_hook 'post-backend'" of the VCS_INFO_formats
# function, where <field> is:
#
# base: the full path of the repository's root directory.
# base-name: the name of the repository's root directory.
# branch: the name of the currently checked out branch.
# misc: a string that may contain anything the vcs_info backend wants.
# revision: an identifier of the currently checked out revision.
# subdir: the path of the current directory relative to the
# repository's root directory.
#
# This patch %-quotes these fields previous to their use in vcs_info hooks and
# the zformat call and, eventually, when they get expanded in the prompt.
# It's important to quote these here, and not later after hooks have modified the
# fields, because then we could be quoting % characters from valid prompt sequences,
# like %F{color}, %B, etc.
#
# 32 │ hook_com[subdir]="$(VCS_INFO_reposub ${hook_com[base]})"
# 33 │ hook_com[subdir_orig]="${hook_com[subdir]}"
# 34 │
# 35 + │ for tmp in base base-name branch misc revision subdir; do
# 36 + │ hook_com[$tmp]="${hook_com[$tmp]//\%/%%}"
# 37 + │ done
# 38 + │
# 39 │ VCS_INFO_hook 'post-backend'
#
# This is especially important so that no command substitution is performed
# due to malicious input as a consequence of CVE-2021-45444, which affects
# zsh versions from 5.0.3 to 5.8.
#
autoload -Uz +X regexp-replace VCS_INFO_formats
# We use $tmp here because it's already a local variable in VCS_INFO_formats
typeset PATCH='for tmp (base base-name branch misc revision subdir) hook_com[$tmp]="${hook_com[$tmp]//\%/%%}"'
# Unique string to avoid reapplying the patch if this code gets called twice
typeset PATCH_ID=vcs_info-patch-9b9840f2-91e5-4471-af84-9e9a0dc68c1b
# Only patch the VCS_INFO_formats function if not already patched
if [[ "$functions[VCS_INFO_formats]" != *$PATCH_ID* ]]; then
regexp-replace 'functions[VCS_INFO_formats]' \
"VCS_INFO_hook 'post-backend'" \
': ${PATCH_ID}; ${PATCH}; ${MATCH}'
fi
unset PATCH PATCH_ID