From: "Johannes Schindelin via GitGitGadget" <gitgitgadget@gmail.com>
To: git@vger.kernel.org
Cc: Elijah Newren <newren@gmail.com>, Taylor Blau <me@ttaylorr.com>,
Johannes Schindelin <johannes.schindelin@gmx.de>
Subject: [PATCH v5 0/2] merge-tree: fix segmentation fault in read-only repositories
Date: Wed, 28 Sep 2022 07:29:20 +0000 [thread overview]
Message-ID: <pull.1362.v5.git.1664350162.gitgitgadget@gmail.com> (raw)
In-Reply-To: <pull.1362.v4.git.1664229348.gitgitgadget@gmail.com>
Turns out that the segmentation fault reported by Taylor
[https://lore.kernel.org/git/YyopQD+LvPucnz3w@nand.local/] happened while
testing merge-ort in a read-only repository, and that the upstream version
of git merge-tree is as affected as GitHub's internal version.
Changes since v4:
* Corrected the commit message that claimed that the second patch was not
fixing a real bug but just avoided unnecessary work. As pointed out by
Elijah, there are scenarios where this second patch fixes a very real
bug.
* Added Elijah's "Reviewed-by" footer.
Changes since v3:
* I now consistently use the pattern int ret = 0; ... if (...) ret = -1.
* I added a commit to properly propagate write failures through the
handle_content_merge() call path, even if it is not really critical (it
just fails sooner, but the merge would have failed just the same without
this patch).
Changes since v2:
* Completely changed the approach by no longer touching
builtin/merge-tree.c but instead fixing the underlying merge-ort layer:
we no longer ignore the return value of write_tree() and
write_object_file().
Changes since v1:
* Using the SANITY prereq now
* If the merge was aborted due to a write error, exit with a non-zero code
even if the (potentially partial) merge is clean
* The test case now also verifies that the git merge-tree command fails in
a read-only repository even if the merge would have succeeded
Johannes Schindelin (2):
merge-ort: fix segmentation fault in read-only repositories
merge-ort: return early when failing to write a blob
merge-ort.c | 94 ++++++++++++++++++++------------
t/t4301-merge-tree-write-tree.sh | 9 +++
2 files changed, 69 insertions(+), 34 deletions(-)
base-commit: dda7228a83e2e9ff584bf6adbf55910565b41e14
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1362%2Fdscho%2Fmerge-tree-in-read-only-repos-v5
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1362/dscho/merge-tree-in-read-only-repos-v5
Pull-Request: https://github.com/gitgitgadget/git/pull/1362
Range-diff vs v4:
1: ab6df092eba ! 1: 63be9f9f717 merge-ort: fix segmentation fault in read-only repositories
@@ Commit message
Let's stop ignoring the return value of `write_object_file()` and
`write_tree()` and set `clean = -1` in the error case.
+ Reviewed-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
## merge-ort.c ##
2: 087207ae0b0 ! 2: bfc71a2d8ad merge-ort: return early when failing to write a blob
@@ Commit message
that already exists in the database). And this can fail, too, but we
ignore that write failure so far.
- Since we will always write out a new tree object in addition to the blob
- (and if the blob did not exist in the database yet, we can be certain
- that the tree object did not exist yet), the merge will _still_ fail at
- that point, but it does unnecessary work by continuing after the blob
- could not be written.
-
Let's pay close attention and error out early if the blob could not be
written. This reduces the error output of t4301.25 ("merge-ort fails
gracefully in a read-only repository") from:
@@ Commit message
error: error: Unable to add numbers to database
fatal: failure to merge
+ This is _not_ just a cosmetic change: Even though one might assume that
+ the operation would have failed anyway at the point when the new tree
+ object is written (and the corresponding tree object _will_ be new if it
+ contains a blob that is new), but that is not so: As pointed out by
+ Elijah Newren, when Git has previously been allowed to add loose objects
+ via `sudo` calls, it is very possible that the blob object cannot be
+ written (because the corresponding `.git/objects/??/` directory may be
+ owned by `root`) but the tree object can be written (because the
+ corresponding objects directory is owned by the current user). This
+ would result in a corrupt repository because it is missing the blob
+ object, and with this here patch we prevent that.
+
Note: This patch adjusts two variable declarations from `unsigned` to
`int` because their purpose is to hold the return value of
`handle_content_merge()`, which is of type `int`. The existing users of
those variables are only interested whether that variable is zero or
non-zero, therefore this type change does not affect the existing code.
+ Reviewed-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
## merge-ort.c ##
--
gitgitgadget
next prev parent reply other threads:[~2022-09-28 7:40 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-21 15:30 [PATCH] merge-tree: fix segmentation fault in read-only repositories Johannes Schindelin via GitGitGadget
2022-09-21 15:42 ` Taylor Blau
2022-09-21 20:12 ` Johannes Schindelin
2022-09-21 18:12 ` Junio C Hamano
2022-09-21 20:13 ` Johannes Schindelin
2022-09-21 22:08 ` [PATCH v2] " Johannes Schindelin via GitGitGadget
2022-09-21 22:24 ` Junio C Hamano
2022-09-22 19:52 ` Johannes Schindelin
2022-09-21 22:56 ` Elijah Newren
2022-09-21 23:11 ` Junio C Hamano
2022-09-22 17:24 ` Johannes Schindelin
2022-09-22 19:50 ` Johannes Schindelin
2022-09-23 1:47 ` Elijah Newren
2022-09-22 19:46 ` [PATCH v3] merge-ort: " Johannes Schindelin via GitGitGadget
2022-09-23 1:38 ` Elijah Newren
2022-09-23 9:55 ` Johannes Schindelin
2022-09-26 21:55 ` [PATCH v4 0/2] merge-tree: " Johannes Schindelin via GitGitGadget
2022-09-26 21:55 ` [PATCH v4 1/2] merge-ort: " Johannes Schindelin via GitGitGadget
2022-09-26 21:55 ` [PATCH v4 2/2] merge-ort: return early when failing to write a blob Johannes Schindelin via GitGitGadget
2022-09-26 22:07 ` Junio C Hamano
2022-09-27 8:05 ` Elijah Newren
2022-09-27 16:45 ` Junio C Hamano
2022-09-27 8:11 ` [PATCH v4 0/2] merge-tree: fix segmentation fault in read-only repositories Elijah Newren
2022-09-28 7:29 ` Johannes Schindelin via GitGitGadget [this message]
2022-09-28 7:29 ` [PATCH v5 1/2] merge-ort: " Johannes Schindelin via GitGitGadget
2022-09-28 7:29 ` [PATCH v5 2/2] merge-ort: return early when failing to write a blob Johannes Schindelin via GitGitGadget
2022-09-28 15:53 ` Junio C Hamano
2022-09-29 1:36 ` Elijah Newren
2022-09-29 1:49 ` Junio C Hamano
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
List information: http://vger.kernel.org/majordomo-info.html
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=pull.1362.v5.git.1664350162.gitgitgadget@gmail.com \
--to=gitgitgadget@gmail.com \
--cc=git@vger.kernel.org \
--cc=johannes.schindelin@gmx.de \
--cc=me@ttaylorr.com \
--cc=newren@gmail.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
Code repositories for project(s) associated with this public inbox
https://80x24.org/mirrors/git.git
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).