[PATCH 0/2] worktree: Fix out of bounds read that causes data loss and reject invalid empty input in worktree add

[PATCH 0/2] worktree: Fix out of bounds read that causes data loss and reject invalid empty input in worktree add

[Matthias Aßhauer via GitGitGadget]

Passing an empty string to git worktree add (typically via an unset
variable, e.g. git worktree add "$UNSET_VAR" -b tb origin/main) can result
in BUG: How come '' becomes empty after sanitization? but it can also have
worse consequences: recursively deleting the current working directory,
including .git. The inconsistent behaviour is caused by worktree_basename
reading unrelated bytes from the memory before path and passing that back to
add_worktree, which can circumvent the check for the BUG call.

Matthias Aßhauer (2):
  worktree: don't read out of bounds
  worktree: reject empty string

 builtin/worktree.c | 20 +++++++++++++-------
 1 file changed, 13 insertions(+), 7 deletions(-)


base-commit: 9a0c4701dcd5725c4184599322b52933ff5005ca
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-2187%2Frimrul%2Fworktree-fix-oob-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-2187/rimrul/worktree-fix-oob-v1
Pull-Request: https://github.com/gitgitgadget/git/pull/2187
-- 
gitgitgadget

[PATCH 1/2] worktree: don't read out of bounds

[Matthias Aßhauer via GitGitGadget]

From: =?UTF-8?q?Matthias=20A=C3=9Fhauer?= <mha1993@live.de>

`worktree_basename` tries to read from memory before the passed `path`
string, if `path` is empty (or only consists of directory separators).
That results in unexpected nonsense data being returned to the caller,
which can lead to issues, such as `git worktree add ""` recursively
deleting the current working directory, including `.git`.

Stop reading out of bounds in these cases to avoid that behaviour.

This leads to `git worktree add ""` consistently exiting with the
message `BUG: How come '' becomes empty after sanitization?`, which is
still undesirable, but at least it doesn't result in data loss anymore.

This fixes https://github.com/git-for-windows/git/issues/6346

Signed-off-by: Matthias Aßhauer <mha1993@live.de>
---
 builtin/worktree.c | 18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/builtin/worktree.c b/builtin/worktree.c
index 4bc7b4f6e7..d8188035db 100644
--- a/builtin/worktree.c
+++ b/builtin/worktree.c
@@ -297,17 +297,21 @@ static void remove_junk_on_signal(int signo)
 static const char *worktree_basename(const char *path, int *olen)
 {
 	const char *name;
-	int len;
+	int len, len2;
 
-	len = strlen(path);
+	len2 = len = strlen(path);
 	while (len && is_dir_sep(path[len - 1]))
 		len--;
 
-	for (name = path + len - 1; name > path; name--)
-		if (is_dir_sep(*name)) {
-			name++;
-			break;
-		}
+	if(len) {
+		for (name = path + len - 1; name > path; name--)
+			if (is_dir_sep(*name)) {
+				name++;
+				break;
+			}
+	}
+	else
+		name = path + len2;
 
 	*olen = len;
 	return name;
-- 
gitgitgadget

[PATCH 2/2] worktree: reject empty string

[Matthias Aßhauer via GitGitGadget]

From: =?UTF-8?q?Matthias=20A=C3=9Fhauer?= <mha1993@live.de>

`git worktree add ""` errors out with the message `BUG: How come ''
becomes empty after sanitization?`, but not due to a bug in the
sanitization code. An empty string should remain empty during
sanitization. Instead reject the argument as invalid user input,
if it's already empty before sanitization.

Signed-off-by: Matthias Aßhauer <mha1993@live.de>
---
 builtin/worktree.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/builtin/worktree.c b/builtin/worktree.c
index d8188035db..113dbf98d3 100644
--- a/builtin/worktree.c
+++ b/builtin/worktree.c
@@ -496,6 +496,8 @@ static int add_worktree(const char *path, const char *refname,
 		die(_("invalid reference: %s"), refname);
 
 	name = worktree_basename(path, &len);
+	if (!len)
+		die(_("the empty string is not a valid worktree"));
 	strbuf_add(&sb, name, path + len - name);
 	sanitize_refname_component(sb.buf, &sb_name);
 	if (!sb_name.len)
-- 
gitgitgadget