Subject: [PATCH] fixup! propagate errno from failing read

From: "Han-Wen Nienhuys via GitGitGadget" <[email-masked]>
Date: Tue, 17 Aug 2021 12:31:29 +0000

From: Han-Wen Nienhuys <[email-masked]>

This fixes a crash triggered by the BUG() statement.

This can occur with symlinked .git/refs. To check availability,
refs_verify_refname_available will run refs_read_raw_ref() on each prefix,
leading to a read() from .git/refs (which is a directory).

When handling the symlink case, it is probably more robust to re-issue the
lstat() as a normal stat(), in which case, we would fall back to the directory
case.

For now, propagating errno from strbuf_read() is simpler and avoids the crash.

Signed-off-by: Han-Wen Nienhuys <[email-masked]>
---
    fixup! propagate errno from failing read
    
    This fixes a crash triggered by the BUG() statement.
    
    This can occur with symlinked .git/refs. To check availability,
    refs_verify_refname_available will run refs_read_raw_ref() on each
    prefix, leading to a read() from .git/refs (which is a directory).
    
    When handling the symlink case, it is probably more robust to re-issue
    the lstat() as a normal stat(), in which case, we would fall back to the
    directory case.
    
    For now, propagating errno from strbuf_read() is simpler and avoids the
    crash.
    
    Signed-off-by: Han-Wen Nienhuys [email-masked]

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-1068%2Fhanwen%2Ffiles-fixup-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-1068/hanwen/files-fixup-v1
Pull-Request: https://github.com/git/git/pull/1068

 refs/files-backend.c |  1 +
 t/t3200-branch.sh    | 14 ++++++++++++++
 2 files changed, 15 insertions(+)

diff --git a/refs/files-backend.c b/refs/files-backend.c
index 0d96eeba61b..f546cc3cc3d 100644
--- a/refs/files-backend.c
+++ b/refs/files-backend.c
@@ -454,6 +454,7 @@ stat_ref:
 	}
 	strbuf_reset(&sb_contents);
 	if (strbuf_read(&sb_contents, fd, 256) < 0) {
+		myerr = errno;
 		close(fd);
 		goto out;
 	}
diff --git a/t/t3200-branch.sh b/t/t3200-branch.sh
index cc4b10236e2..dd17718160a 100755
--- a/t/t3200-branch.sh
+++ b/t/t3200-branch.sh
@@ -109,6 +109,20 @@ test_expect_success 'git branch -m n/n n should work' '
 	git reflog exists refs/heads/n
 '
 
+test_expect_success 'git branch -m with symlinked .git/refs' '
+	git init subdir &&
+	test_when_finished "rm -rf subdir" &&
+	(cd subdir &&
+		for d in refs objects packed-refs ; do
+		rm -rf .git/$d &&
+		ln -s ../../.git/$d .git/$d ; done ) &&
+	git --git-dir subdir/.git/ branch rename-src &&
+	expect=$(git rev-parse rename-src) &&
+	git --git-dir subdir/.git/ branch -m rename-src rename-dest &&
+	test $(git rev-parse rename-dest) = "$expect" &&
+	git branch -D rename-dest
+'
+
 # The topmost entry in reflog for branch bbb is about branch creation.
 # Hence, we compare bbb@{1} (instead of bbb@{0}) with aaa@{0}.

base-commit: f000ecbed922c727382651490e75014f003c89ca
-- 
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