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Fix a Time-of-check to time-of-use (TOCTOU) race in code added in
680ee550d72 (commit: skip discarding the index if there is no
pre-commit hook, 2017-08-14).
This obscure race condition can occur if we e.g. ran the "pre-commit"
hook and it modified the index, but hook_exists() returns false later
on (e.g., because the hook itself went away, the directory became
unreadable, etc.). Then we won't call discard_cache() when we should
have.
The race condition itself probably doesn't matter, and users would
have been unlikely to run into it in practice. This problem has been
noted on-list when 680ee550d72 was discussed[1], but had not been
fixed.
This change is mainly intended to improve the readability of the code
involved, and to make reasoning about it more straightforward. It
wasn't as obvious what we were trying to do here, but by having an
"invoked_hook" it's clearer that e.g. our discard_cache() is happening
because of the earlier hook execution.
Let's also change this for the push-to-checkout hook. Now instead of
checking if the hook exists and either doing a push to checkout or a
push to deploy we'll always attempt a push to checkout. If the hook
doesn't exist we'll fall back on push to deploy. The same behavior as
before, without the TOCTOU race. See 0855331941b (receive-pack:
support push-to-checkout hook, 2014-12-01) for the introduction of the
previous behavior.
This leaves uses of hook_exists() in two places that matter. The
"reference-transaction" check in refs.c, see 67541597670 (refs:
implement reference transaction hook, 2020-06-19), and the
"prepare-commit-msg" hook, see 66618a50f9c (sequencer: run
'prepare-commit-msg' hook, 2018-01-24).
In both of those cases we're saving ourselves CPU time by not
preparing data for the hook that we'll then do nothing with if we
don't have the hook. So using this "invoked_hook" pattern doesn't make
sense in those cases.
The "reference-transaction" and "prepare-commit-msg" hook also aren't
racy. In those cases we'll skip the hook runs if we race with a new
hook being added, whereas in the TOCTOU races being fixed here we were
incorrectly skipping the required post-hook logic.
1. https://lore.kernel.org/git/20170810191613.kpmhzg4seyxy3cpq@sigill.intra.peff.net/
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Move the running of the 'post-checkout' hook away from run-command.h
to the new hook.h library in builtin/worktree.c. For this special case
we need a change to the hook API to teach it to run the hook from a
given directory.
We cannot skip the "absolute_path" flag and just check if "dir" is
specified as we'd then fail to find our hook in the new dir we'd
chdir() to. We currently don't have a use-case for running a hook not
in our "base" repository at a given absolute path, so let's have "dir"
imply absolute_path(find_hook(hook_name)).
Signed-off-by: Emily Shaffer <emilyshaffer@google.com>
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Acked-by: Emily Shaffer <emilyshaffer@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Add a run_hooks_l() wrapper, we'll use it in subsequent commits for
the simple cases of wanting to run a single hook under a given name
along with a list of arguments.
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Reviewed-by: Emily Shaffer <emilyshaffer@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Add a run_hooks() wrapper, we'll use it in subsequent commits for the
simple cases of wanting to run a single hook under a given name,
without providing options such as "env" or "args".
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Reviewed-by: Emily Shaffer <emilyshaffer@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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In order to enable hooks to be run as an external process, by a
standalone Git command, or by tools which wrap Git, provide an external
means to run all configured hook commands for a given hook event.
Most of our hooks require more complex functionality than this, but
let's start with the bare minimum required to support our simplest
hooks.
In terms of implementation the usage_with_options() and "goto usage"
pattern here mirrors that of
builtin/{commit-graph,multi-pack-index}.c.
Some of the implementation here, such as a function being named
run_hooks_opt() when it's tasked with running one hook, to using the
run_processes_parallel_tr2() API to run with jobs=1 is somewhere
between a bit odd and and an overkill for the current features of this
"hook run" command and the hook.[ch] API.
This code will eventually be able to run multiple hooks declared in
config in parallel, by starting out with these names and APIs we
reduce the later churn of renaming functions, switching from the
run_command() to run_processes_parallel_tr2() API etc.
Signed-off-by: Emily Shaffer <emilyshaffer@google.com>
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Acked-by: Emily Shaffer <emilyshaffer@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Add a boolean version of the find_hook() function for those callers
who are only interested in checking whether the hook exists, not what
the path to it is.
Signed-off-by: Emily Shaffer <emilyshaffer@google.com>
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Move the find_hook() function from run-command.c to a new hook.c
library. This change establishes a stub library that's pretty
pointless right now, but will see much wider use with Emily Shaffer's
upcoming "configuration-based hooks" series.
Eventually all the hook related code will live in hook.[ch]. Let's
start that process by moving the simple find_hook() function over
as-is.
Signed-off-by: Emily Shaffer <emilyshaffer@google.com>
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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