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Jeff King 6479ea4a8a xrealloc: do not reuse pointer freed by zero-length realloc()
This patch fixes a bug where xrealloc(ptr, 0) can double-free and
corrupt the heap on some platforms (including at least glibc).

The C99 standard says of malloc (section 7.20.3):

  If the size of the space requested is zero, the behavior is
  implementation-defined: either a null pointer is returned, or the
  behavior is as if the size were some nonzero value, except that the
  returned pointer shall not be used to access an object.

So we might get NULL back, or we might get an actual pointer (but we're
not allowed to look at its contents). To simplify our code, our
xmalloc() handles a NULL return by converting it into a single-byte
allocation. That way callers get consistent behavior. This was done way
back in 4e7a2eccc2 (?alloc: do not return NULL when asked for zero
bytes, 2005-12-29).

We also gave xcalloc() and xrealloc() the same treatment. And according
to C99, that is fine; the text above is in a paragraph that applies to
all three. But what happens to the memory we passed to realloc() in such
a case? I.e., if we do:

  ret = realloc(ptr, 0);

and "ptr" is non-NULL, but we get NULL back, is "ptr" still valid? C99
doesn't cover this case specifically, but says (section 7.20.3.4):

  The realloc function deallocates the old object pointed to by ptr and
  returns a pointer to a new object that has the size specified by size.

So "ptr" is now deallocated, and we must only look at "ret". And since
"ret" is NULL, that means we have no allocated object at all. But that's
not quite the whole story. It also says:

  If memory for the new object cannot be allocated, the old object is
  not deallocated and its value is unchanged.
  [...]
  The realloc function returns a pointer to the new object (which may
  have the same value as a pointer to the old object), or a null pointer
  if the new object could not be allocated.

So if we see a NULL return with a non-zero size, we can expect that the
original object _is_ still valid. But with a non-zero size, it's
ambiguous. The NULL return might mean a failure (in which case the
object is valid), or it might mean that we successfully allocated
nothing, and used NULL to represent that.

The glibc manpage for realloc() explicitly says:

  [...]if size is equal to zero, and ptr is not NULL, then the call is
  equivalent to free(ptr).

Likewise, this StackOverflow answer:

  https://stackoverflow.com/a/2135302

claims that C89 gave similar guidance (but I don't have a copy to verify
it). A comment on this answer:

  https://stackoverflow.com/a/2022410

claims that Microsoft's CRT behaves the same.

But our current "retry with 1 byte" code passes the original pointer
again. So on glibc, we effectively free() the pointer and then try to
realloc() it again, which is undefined behavior.

The simplest fix here is to just pass "ret" (which we know to be NULL)
to the follow-up realloc(). But that means that a system which _doesn't_
free the original pointer would leak it. It's not clear if any such
systems exist, and that interpretation of the standard seems unlikely
(I'd expect a system that doesn't deallocate to simply return the
original pointer in this case). But it's easy enough to err on the safe
side, and just never pass a zero size to realloc() at all.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2020-09-02 12:18:14 -07:00
.github Merge branch 'es/advertise-contribution-doc' 2020-06-17 21:54:06 -07:00
block-sha1
builtin Merge branch 'tb/commit-graph-no-check-oids' into master 2020-07-15 16:29:45 -07:00
ci Merge branch 'jk/ci-only-on-selected-branches' 2020-05-29 15:12:19 -07:00
compat Merge branch 'js/msvc-build-fix' 2020-06-17 21:54:03 -07:00
contrib Merge branch 'en/sparse-status' into master 2020-07-21 14:19:10 -07:00
Documentation Merge branch 'ps/ref-transaction-hook' into master 2020-07-24 15:54:06 -07:00
ewah
git-gui Merge https://github.com/prati0100/git-gui into master 2020-07-20 12:04:06 -07:00
gitk-git
gitweb Merge branch 'eb/gitweb-more-trailers' 2020-05-01 13:39:56 -07:00
mergetools
negotiator
perl perl: make SVN code hash independent 2020-06-22 11:21:07 -07:00
po Merge branch 'master' of github.com:Softcatala/git-po 2020-07-27 00:05:41 +08:00
ppc
refs refs: improve documentation for ref iterator 2020-05-20 10:39:02 -07:00
sha1collisiondetection@855827c583
sha1dc
sha256
t Merge branch 'dl/branch-cleanup' into master 2020-07-18 16:35:22 -07:00
templates
trace2
vcs-svn
xdiff
.cirrus.yml
.clang-format
.editorconfig
.gitattributes
.gitignore Merge branch 'es/bugreport' 2020-05-01 13:39:59 -07:00
.gitmodules
.mailmap
.travis.yml
.tsan-suppressions
abspath.c
aclocal.m4
add-interactive.c
add-interactive.h
add-patch.c Merge branch 'js/checkout-p-new-file' 2020-06-08 18:06:31 -07:00
advice.c
advice.h
alias.c
alias.h
alloc.c commit: move members graph_pos, generation to a slab 2020-06-17 14:37:30 -07:00
alloc.h object: drop parsed_object_pool->commit_count 2020-06-17 14:37:14 -07:00
apply.c Use OPT_CALLBACK and OPT_CALLBACK_F 2020-04-28 10:47:10 -07:00
apply.h
archive-tar.c
archive-zip.c
archive.c
archive.h
argv-array.c
argv-array.h
attr.c
attr.h
banned.h
base85.c
bisect.c
bisect.h
blame.c commit: move members graph_pos, generation to a slab 2020-06-17 14:37:30 -07:00
blame.h
blob.c object: drop parsed_object_pool->commit_count 2020-06-17 14:37:14 -07:00
blob.h
bloom.c commit-graph: minimize commit_graph_data_slab access 2020-06-17 14:37:52 -07:00
bloom.h Merge branch 'ds/line-log-on-bloom' 2020-06-08 18:06:26 -07:00
branch.c Merge branch 'es/get-worktrees-unsort' 2020-07-06 22:09:15 -07:00
branch.h
bugreport.c Merge branch 'rs/retire-strbuf-write-fd' 2020-06-29 14:17:26 -07:00
builtin.h
bulk-checkin.c
bulk-checkin.h
bundle.c bundle: detect hash algorithm when reading refs 2020-06-19 14:04:09 -07:00
bundle.h bundle: detect hash algorithm when reading refs 2020-06-19 14:04:09 -07:00
cache-tree.c
cache-tree.h
cache.h Merge branch 'jn/v0-with-extensions-fix' into master 2020-07-16 17:58:42 -07:00
chdir-notify.c
chdir-notify.h
check_bindir
check-builtins.sh
checkout.c
checkout.h
CODE_OF_CONDUCT.md
color.c
color.h
column.c
column.h
combine-diff.c
command-list.txt bash-completion: add git-prune into bash completion 2020-06-22 11:29:38 -07:00
commit-graph.c Merge branch 'sg/commit-graph-progress-fix' into master 2020-07-15 16:29:43 -07:00
commit-graph.h commit-graph: introduce commit_graph_data_slab 2020-06-17 14:37:23 -07:00
commit-reach.c Merge branch 'cb/is-descendant-of' 2020-07-06 22:09:16 -07:00
commit-reach.h commit-reach: avoid is_descendant_of() shim 2020-06-23 16:36:53 -07:00
commit-slab-decl.h commit-slab-decl.h: update include guard 2020-05-18 10:33:00 -07:00
commit-slab-impl.h
commit-slab.h
commit.c Merge branch 'tb/fix-persistent-shallow' into master 2020-07-09 14:00:44 -07:00
commit.h commit: move members graph_pos, generation to a slab 2020-06-17 14:37:30 -07:00
common-main.c
config.c
config.h
config.mak.dev
config.mak.in
config.mak.uname Merge branch 'cb/no-more-gmtime' 2020-05-20 08:33:27 -07:00
configure.ac
connect.c Merge branch 'bc/sha-256-part-2' 2020-07-06 22:09:13 -07:00
connect.h Merge branch 'bc/sha-256-part-2' 2020-07-06 22:09:13 -07:00
connected.c fetch-pack: support more than one pack lockfile 2020-06-10 18:06:34 -07:00
connected.h
convert.c
convert.h
copy.c
COPYING
credential-cache--daemon.c
credential-cache.c
credential-store.c Merge branch 'cb/credential-store-ignore-bogus-lines' 2020-05-08 14:25:01 -07:00
credential.c Merge branch 'js/partial-urlmatch' 2020-05-05 14:54:30 -07:00
credential.h credential: correct order of parameters for credential_match 2020-05-04 22:56:33 -07:00
csum-file.c
csum-file.h
ctype.c
daemon.c
date.c date.c: allow compact version of ISO-8601 datetime 2020-04-24 14:06:09 -07:00
decorate.c
decorate.h
delta-islands.c
delta-islands.h
delta.h
detect-compiler
diff-delta.c
diff-lib.c diff-files --raw: show correct post-image of intent-to-add files 2020-07-01 16:15:43 -07:00
diff-no-index.c
diff.c Merge branch 'jk/diff-memuse-optim-with-stat-unmatch' 2020-06-17 21:54:00 -07:00
diff.h
diffcore-break.c
diffcore-delta.c
diffcore-order.c
diffcore-pickaxe.c
diffcore-rename.c
diffcore.h
dir-iterator.c
dir-iterator.h
dir.c Merge branch 'en/clean-cleanups' 2020-06-25 12:27:45 -07:00
dir.h
editor.c
entry.c Merge branch 'mt/entry-fstat-fallback-fix' into master 2020-07-09 14:00:45 -07:00
environment.c Merge branch 'tb/shallow-cleanup' 2020-05-13 12:19:18 -07:00
exec-cmd.c
exec-cmd.h
fast-import.c Merge branch 'en/fast-import-looser-date' 2020-06-02 13:35:05 -07:00
fetch-negotiator.c
fetch-negotiator.h
fetch-pack.c Merge branch 'bc/sha-256-part-2' 2020-07-06 22:09:13 -07:00
fetch-pack.h fetch-pack: support more than one pack lockfile 2020-06-10 18:06:34 -07:00
fmt-merge-msg.c fmt-merge-msg: stop treating master specially 2020-06-23 17:22:35 -07:00
fmt-merge-msg.h
fsck.c Merge branch 'rs/fsck-duplicate-names-in-trees' 2020-06-08 18:06:29 -07:00
fsck.h
fsmonitor.c
fsmonitor.h
fuzz-commit-graph.c fuzz-commit-graph: properly free graph struct 2020-06-08 10:02:29 -07:00
fuzz-pack-headers.c
fuzz-pack-idx.c
generate-cmdlist.sh
generate-configlist.sh
gettext.c
gettext.h
git-add--interactive.perl checkout -p: handle new files correctly 2020-05-27 14:50:20 -07:00
git-archimport.perl
git-bisect.sh bisect: avoid tailing CR characters from revision in replay 2020-05-20 10:13:19 -07:00
git-compat-util.h Merge branch 'bc/sha-256-part-2' 2020-07-06 22:09:13 -07:00
git-cvsexportcommit.perl git-cvsexportcommit: port to SHA-256 2020-06-22 11:21:07 -07:00
git-cvsimport.perl git-cvsimport: port to SHA-256 2020-06-22 11:21:07 -07:00
git-cvsserver.perl git-cvsserver: port to SHA-256 2020-06-22 11:21:07 -07:00
git-difftool--helper.sh
git-filter-branch.sh
git-instaweb.sh
git-merge-octopus.sh
git-merge-one-file.sh
git-merge-resolve.sh
git-mergetool--lib.sh
git-mergetool.sh
git-p4.py Merge branch 'bk/p4-prepare-p4-only-fix' 2020-06-02 13:35:01 -07:00
git-parse-remote.sh
git-quiltimport.sh
git-rebase--preserve-merges.sh
git-request-pull.sh
git-send-email.perl send-email: restore --in-reply-to superseding behavior 2020-07-01 16:12:21 -07:00
git-sh-i18n.sh
git-sh-setup.sh
git-submodule.sh submodule: port subcommand 'set-branch' from shell to C 2020-06-02 10:51:54 -07:00
git-svn.perl git-svn: set the OID length based on hash algorithm 2020-06-22 11:21:07 -07:00
GIT-VERSION-GEN Git 2.28 2020-07-26 18:01:43 -07:00
git-web--browse.sh
git.c Merge branch 'ta/wait-on-aliased-commands-upon-signal' into master 2020-07-15 16:29:43 -07:00
git.rc
gpg-interface.c
gpg-interface.h
graph.c graph.c: limit linkage of internal variable 2020-04-27 11:21:25 -07:00
graph.h
grep.c
grep.h
hash.h
hashmap.c
hashmap.h
help.c help: add shell-path to --build-options 2020-05-12 22:02:17 -07:00
help.h
hex.c
http-backend.c
http-fetch.c http-fetch: support fetching packfiles by URL 2020-06-10 18:06:34 -07:00
http-push.c Merge branch 'bc/http-push-flagsfix' 2020-07-06 22:09:17 -07:00
http-walker.c http: refactor finish_http_pack_request() 2020-06-10 18:06:34 -07:00
http.c Merge branch 'jt/cdn-offload' 2020-06-25 12:27:47 -07:00
http.h Merge branch 'jt/cdn-offload' 2020-06-25 12:27:47 -07:00
ident.c
imap-send.c http, imap-send: stop using CURLOPT_VERBOSE 2020-05-11 11:18:01 -07:00
INSTALL
interdiff.c
interdiff.h
iterator.h
json-writer.c
json-writer.h
khash.h
kwset.c
kwset.h
levenshtein.c
levenshtein.h
LGPL-2.1
line-log.c Merge branch 'ds/line-log-on-bloom' 2020-06-08 18:06:26 -07:00
line-log.h line-log: more responsive, incremental 'git log -L' 2020-05-11 09:33:56 -07:00
line-range.c
line-range.h
linear-assignment.c
linear-assignment.h
list-objects-filter-options.c repository: add a helper function to perform repository format upgrade 2020-06-05 10:13:30 -07:00
list-objects-filter-options.h Use OPT_CALLBACK and OPT_CALLBACK_F 2020-04-28 10:47:10 -07:00
list-objects-filter.c list-objects-filter: treat NULL filter_options as "disabled" 2020-05-04 21:57:58 -07:00
list-objects-filter.h
list-objects.c
list-objects.h
list.h
ll-merge.c
ll-merge.h
lockfile.c lockfile.c: introduce 'hold_lock_file_for_update_mode' 2020-04-27 11:27:36 -07:00
lockfile.h lockfile.c: introduce 'hold_lock_file_for_update_mode' 2020-04-27 11:27:36 -07:00
log-tree.c Merge branch 'ds/log-exclude-decoration-config' 2020-04-28 15:50:08 -07:00
log-tree.h
ls-refs.c
ls-refs.h
mailinfo.c mailinfo: disallow NUL character in mail's header 2020-04-22 14:01:03 -07:00
mailinfo.h
mailmap.c
mailmap.h
Makefile Merge branch 'lo/sparse-universal-zero-init' 2020-06-02 13:35:04 -07:00
match-trees.c
mem-pool.c
mem-pool.h
merge-blobs.c
merge-blobs.h
merge-recursive.c merge-recursive: fix rename/rename(1to2) for working tree with a binary 2020-05-14 12:14:19 -07:00
merge-recursive.h
merge.c
mergesort.c
mergesort.h
midx.c multi-pack-index: respect repack.packKeptObjects=false 2020-05-10 09:50:55 -07:00
midx.h Merge branch 'ds/multi-pack-index' 2020-05-01 13:39:55 -07:00
name-hash.c
notes-cache.c
notes-cache.h
notes-merge.c
notes-merge.h
notes-utils.c
notes-utils.h
notes.c
notes.h
object-store.h packfile: compute and use the index CRC offset 2020-05-27 10:07:07 -07:00
object.c object: drop parsed_object_pool->commit_count 2020-06-17 14:37:14 -07:00
object.h Merge branch 'tb/fix-persistent-shallow' into master 2020-07-09 14:00:44 -07:00
oid-array.c
oid-array.h oid_array: rename source file from sha1-array 2020-03-30 10:59:08 -07:00
oidmap.c
oidmap.h
oidset.c
oidset.h Merge branch 'tb/commit-graph-split-strategy' 2020-05-01 13:39:52 -07:00
pack-bitmap-write.c
pack-bitmap.c pack-bitmap: pass object filter to fill-in traversal 2020-05-04 21:57:58 -07:00
pack-bitmap.h
pack-check.c
pack-objects.c
pack-objects.h
pack-revindex.c
pack-revindex.h
pack-write.c
pack.h
packfile.c packfile: compute and use the index CRC offset 2020-05-27 10:07:07 -07:00
packfile.h
pager.c
parse-options-cb.c
parse-options.c
parse-options.h
patch-delta.c
patch-ids.c
patch-ids.h
path.c Merge branch 'dl/merge-autostash' 2020-04-29 16:15:27 -07:00
path.h
pathspec.c
pathspec.h
pkt-line.c Merge branch 'bc/sha-256-part-2' 2020-07-06 22:09:13 -07:00
pkt-line.h Merge branch 'bc/sha-256-part-2' 2020-07-06 22:09:13 -07:00
preload-index.c
pretty.c
pretty.h
prio-queue.c prio-queue: add 'peek' operation 2018-11-02 12:14:21 +09:00
prio-queue.h
progress.c progress: call trace2_region_leave() only after calling _enter() 2020-05-15 09:41:30 -07:00
progress.h progress.c: silence cgcc suggestion about internal linkage 2020-04-27 11:21:28 -07:00
promisor-remote.c Merge branch 'jt/avoid-prefetch-when-able-in-diff' 2020-04-28 15:50:04 -07:00
promisor-remote.h
prompt.c
prompt.h
protocol.c config: let feature.experimental imply protocol.version=2 2020-05-21 09:31:42 -07:00
protocol.h
prune-packed.c
prune-packed.h
quote.c
quote.h
range-diff.c
range-diff.h
reachable.c
reachable.h
read-cache.c
README.md
rebase-interactive.c
rebase-interactive.h
rebase.c
rebase.h
ref-filter.c Merge branch 'es/get-worktrees-unsort' 2020-07-06 22:09:15 -07:00
ref-filter.h Merge branch 'jk/for-each-ref-multi-key-sort-fix' 2020-05-08 14:25:04 -07:00
reflog-walk.c
reflog-walk.h
refs.c Merge branch 'js/default-branch-name' 2020-07-06 22:09:17 -07:00
refs.h Merge branch 'js/default-branch-name' 2020-07-06 22:09:17 -07:00
refspec.c
refspec.h
RelNotes Start the post 2.27 cycle 2020-06-02 13:35:05 -07:00
remote-curl.c Merge branch 'bc/sha-256-part-2' 2020-07-06 22:09:13 -07:00
remote-testsvn.c testsvn: respect init.defaultBranch 2020-06-24 09:14:21 -07:00
remote.c remote: use the configured default branch name when appropriate 2020-06-24 09:14:21 -07:00
remote.h stateless-connect: send response end packet 2020-05-24 16:26:00 -07:00
replace-object.c
replace-object.h
repo-settings.c experimental: default to fetch.writeCommitGraph=false 2020-07-08 16:37:43 -07:00
repository.c
repository.h repository: add a helper function to perform repository format upgrade 2020-06-05 10:13:30 -07:00
rerere.c
rerere.h
reset.c Merge branch 'dl/merge-autostash' 2020-04-29 16:15:27 -07:00
reset.h
resolve-undo.c
resolve-undo.h
revision.c Merge branch 'rs/line-log-until' into master 2020-07-09 14:00:42 -07:00
revision.h revision: reallocate TOPO_WALK object flags 2020-06-24 09:09:44 -07:00
run-command.c Merge branch 'ta/wait-on-aliased-commands-upon-signal' into master 2020-07-15 16:29:43 -07:00
run-command.h Merge branch 'ta/wait-on-aliased-commands-upon-signal' into master 2020-07-15 16:29:43 -07:00
send-pack.c Merge branch 'js/default-branch-name' 2020-07-06 22:09:17 -07:00
send-pack.h
sequencer.c Merge branch 'js/rebase-autosquash-double-fixup-fix' 2020-05-14 14:39:43 -07:00
sequencer.h Merge branch 'dl/merge-autostash' 2020-04-29 16:15:27 -07:00
serve.c Merge branch 'bc/sha-256-part-2' 2020-07-06 22:09:13 -07:00
serve.h
server-info.c
setup.c Merge branch 'jn/v0-with-extensions-fix' into master 2020-07-16 17:58:42 -07:00
sh-i18n--envsubst.c
sha1-file.c Merge branch 'lr/freshen-file-fix' 2020-04-28 15:49:56 -07:00
sha1-lookup.c
sha1-lookup.h
sha1-name.c Merge branch 'jc/missing-ref-store-fix' 2020-04-22 13:42:55 -07:00
sha1dc_git.c
sha1dc_git.h
shallow.c Merge branch 'tb/shallow-cleanup' 2020-05-13 12:19:18 -07:00
shallow.h shallow: use struct 'shallow_lock' for additional safety 2020-04-30 14:19:13 -07:00
shell.c
shortlog.h
sideband.c
sideband.h
sigchain.c
sigchain.h
split-index.c
split-index.h
stable-qsort.c
strbuf.c Merge branch 'rs/retire-strbuf-write-fd' 2020-06-29 14:17:26 -07:00
strbuf.h Merge branch 'rs/retire-strbuf-write-fd' 2020-06-29 14:17:26 -07:00
streaming.c
streaming.h
string-list.c
string-list.h
sub-process.c
sub-process.h
submodule-config.c
submodule-config.h
submodule.c
submodule.h
symlinks.c
tag.c object: drop parsed_object_pool->commit_count 2020-06-17 14:37:14 -07:00
tag.h
tar.h
tempfile.c tempfile.c: introduce 'create_tempfile_mode' 2020-04-27 11:27:35 -07:00
tempfile.h tempfile.c: introduce 'create_tempfile_mode' 2020-04-27 11:27:35 -07:00
thread-utils.c
thread-utils.h
tmp-objdir.c
tmp-objdir.h
trace2.c
trace2.h
trace.c http, imap-send: stop using CURLOPT_VERBOSE 2020-05-11 11:18:01 -07:00
trace.h http, imap-send: stop using CURLOPT_VERBOSE 2020-05-11 11:18:01 -07:00
trailer.c
trailer.h
transport-helper.c Merge branch 'js/default-branch-name' 2020-07-06 22:09:17 -07:00
transport-internal.h
transport.c Merge branch 'bc/sha-256-part-2' 2020-07-06 22:09:13 -07:00
transport.h Merge branch 'bc/sha-256-part-2' 2020-07-06 22:09:13 -07:00
tree-diff.c
tree-walk.c
tree-walk.h
tree.c object: drop parsed_object_pool->commit_count 2020-06-17 14:37:14 -07:00
tree.h
unicode-width.h
unimplemented.sh
unix-socket.c
unix-socket.h
unpack-trees.c Merge branch 'en/sparse-checkout' 2020-05-20 08:33:29 -07:00
unpack-trees.h Merge branch 'en/sparse-checkout' 2020-04-29 16:15:30 -07:00
upload-pack.c Merge branch 'bc/sha-256-part-2' 2020-07-06 22:09:13 -07:00
upload-pack.h
url.c
url.h
urlmatch.c credential: handle credential.<partial-URL>.<key> again 2020-04-24 15:53:46 -07:00
urlmatch.h credential: handle credential.<partial-URL>.<key> again 2020-04-24 15:53:46 -07:00
usage.c
userdiff.c Merge branch 'ah/userdiff-markdown' 2020-05-08 14:25:01 -07:00
userdiff.h
utf8.c
utf8.h
varint.c
varint.h
version.c
version.h
versioncmp.c
walker.c
walker.h
wildmatch.c
wildmatch.h
worktree.c Merge branch 'es/worktree-code-cleanup' 2020-07-06 22:09:19 -07:00
worktree.h worktree: drop get_worktrees() unused 'flags' argument 2020-06-22 10:31:15 -07:00
wrap-for-bin.sh
wrapper.c xrealloc: do not reuse pointer freed by zero-length realloc() 2020-09-02 12:18:14 -07:00
write-or-die.c
ws.c
wt-status.c wt-status: show sparse checkout status as well 2020-06-18 14:12:28 -07:00
wt-status.h wt-status: show sparse checkout status as well 2020-06-18 14:12:28 -07:00
xdiff-interface.c
xdiff-interface.h
zlib.c

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Git - fast, scalable, distributed revision control system

Git is a fast, scalable, distributed revision control system with an unusually rich command set that provides both high-level operations and full access to internals.

Git is an Open Source project covered by the GNU General Public License version 2 (some parts of it are under different licenses, compatible with the GPLv2). It was originally written by Linus Torvalds with help of a group of hackers around the net.

Please read the file INSTALL for installation instructions.

Many Git online resources are accessible from https://git-scm.com/ including full documentation and Git related tools.

See Documentation/gittutorial.txt to get started, then see Documentation/giteveryday.txt for a useful minimum set of commands, and Documentation/git-<commandname>.txt for documentation of each command. If git has been correctly installed, then the tutorial can also be read with man gittutorial or git help tutorial, and the documentation of each command with man git-<commandname> or git help <commandname>.

CVS users may also want to read Documentation/gitcvs-migration.txt (man gitcvs-migration or git help cvs-migration if git is installed).

The user discussion and development of Git take place on the Git mailing list -- everyone is welcome to post bug reports, feature requests, comments and patches to git@vger.kernel.org (read Documentation/SubmittingPatches for instructions on patch submission). To subscribe to the list, send an email with just "subscribe git" in the body to majordomo@vger.kernel.org. The mailing list archives are available at https://lore.kernel.org/git/, http://marc.info/?l=git and other archival sites.

Issues which are security relevant should be disclosed privately to the Git Security mailing list git-security@googlegroups.com.

The maintainer frequently sends the "What's cooking" reports that list the current status of various development topics to the mailing list. The discussion following them give a good reference for project status, development direction and remaining tasks.

The name "git" was given by Linus Torvalds when he wrote the very first version. He described the tool as "the stupid content tracker" and the name as (depending on your mood):

  • random three-letter combination that is pronounceable, and not actually used by any common UNIX command. The fact that it is a mispronunciation of "get" may or may not be relevant.
  • stupid. contemptible and despicable. simple. Take your pick from the dictionary of slang.
  • "global information tracker": you're in a good mood, and it actually works for you. Angels sing, and a light suddenly fills the room.
  • "goddamn idiotic truckload of sh*t": when it breaks