[PATCH 3/9] csum-file: always finalize or discard hash

[Jeff King <peff@peff.net>]

When a hashfile struct is created, we always initialize the git_hash_ctx
inside it. We usually end up in hashfile_finalize(), which passes that
ctx to git_hash_final(), cleaning it up.

But a few code paths don't do so:

  1. If we bail on the hashfile and call free_hashfile() directly rather
     than finalizing.

  2. If the skip_hash flag is set, the hashfile_finalize() call will
     never call git_hash_final(). (You might think that we should just
     avoid git_hash_init() entirely in this case, but the skip_hash flag
     is set by the caller after the hashfile is initialized).

For most hash implementations this is OK, but for ones that allocate on
initialization it causes a memory leak. You can see many failures by
running:

  make SANITIZE=leak OPENSSL_SHA1_UNSAFE=1 test

since OpenSSL >= 3.0 is such an allocating hash implementation (and
csum-file uses the "unsafe" algorithm variant).

We can solve this by calling git_hash_discard() as appropriate.

Note that free_hashfile() is used both directly by callers to abort
without finalizing, and by hashfile_finalize() to free memory. In the
latter case we _don't_ want to call git_hash_discard(), because we'll
already have either finalized or discarded it. So we'll push that to an
internal "free_memory" function, and keep free_hashfile() as the public
interface to abort a hashfile without finalizing.

This fix makes several scripts leak-free with the command above: t1600,
t1601, t2107, t7008, t9210, t9211.

Signed-off-by: Jeff King <peff@peff.net>
---
 csum-file.c | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/csum-file.c b/csum-file.c
index 8ca9246a80..44ff460692 100644
--- a/csum-file.c
+++ b/csum-file.c
@@ -55,24 +55,32 @@ void hashflush(struct hashfile *f)
 	}
 }
 
-void free_hashfile(struct hashfile *f)
+static void free_hashfile_memory(struct hashfile *f)
 {
 	free(f->buffer);
 	free(f->check_buffer);
 	free(f);
 }
 
+void free_hashfile(struct hashfile *f)
+{
+	git_hash_discard(&f->ctx);
+	free_hashfile_memory(f);
+}
+
 int finalize_hashfile(struct hashfile *f, unsigned char *result,
 		      enum fsync_component component, unsigned int flags)
 {
 	int fd;
 
 	hashflush(f);
 
-	if (f->skip_hash)
+	if (f->skip_hash) {
+		git_hash_discard(&f->ctx);
 		hashclr(f->buffer, f->algop);
-	else
+	} else {
 		git_hash_final(f->buffer, &f->ctx);
+	}
 
 	if (result)
 		hashcpy(result, f->buffer, f->algop);
@@ -97,7 +105,7 @@ int finalize_hashfile(struct hashfile *f, unsigned char *result,
 		if (close(f->check_fd))
 			die_errno("%s: sha1 file error on close", f->name);
 	}
-	free_hashfile(f);
+	free_hashfile_memory(f);
 	return fd;
 }
 
-- 
2.55.0.418.g37da59dd42