refs: strip out not allowed flags from ref_transaction_update

Callers are only allowed to pass certain flags into
ref_transaction_update, other flags are internal to it.  To prevent
mistakes from the callers, strip the internal only flags out before
continuing.

This was noticed because of a compiler warning gcc 7.1.1 issued about
passing a NULL parameter as second parameter to memcpy (through
hashcpy):

In file included from refs.c:5:0:
refs.c: In function ‘ref_transaction_verify’:
cache.h:948:2: error: argument 2 null where non-null expected [-Werror=nonnull]
memcpy(sha_dst, sha_src, GIT_SHA1_RAWSZ);
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from git-compat-util.h:165:0,
from cache.h:4,
from refs.c:5:
/usr/include/string.h:43:14: note: in a call to function ‘memcpy’ declared here
extern void *memcpy (void *__restrict __dest, const void *__restrict __src,
^~~~~~

The call to hascpy in ref_transaction_add_update is protected by the
passed in flags, but as we only add flags there, gcc notices
REF_HAVE_NEW or REF_HAVE_OLD flags could be passed in from the outside,
which would potentially result in passing in NULL as second parameter to
memcpy.

Fix both the compiler warning, and make the interface safer for its
users by stripping the internal flags out.

Suggested-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Thomas Gummerer <t.gummerer@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/refs.c b/refs.c
index ea2b9f84f8d3fab5452105f10f4492d672cd1d90..41aec6505d1309fa2efed2bd9aca0a0ef2646444 100644 (file)
--- a/refs.c
+++ b/refs.c
@@ -921,6 +921,8 @@ int ref_transaction_update(struct ref_transaction *transaction,
                return -1;
        }
 
+       flags &= REF_TRANSACTION_UPDATE_ALLOWED_FLAGS;
+
        flags |= (new_sha1 ? REF_HAVE_NEW : 0) | (old_sha1 ? REF_HAVE_OLD : 0);
 
        ref_transaction_add_update(transaction, refname, flags,

diff --git a/refs.h b/refs.h
index 6daa78eb50ddc195c6d5bfb568d0b05ab08f7923..4d75c207e18bd6504a5613a373adf9dd8c745034 100644 (file)
--- a/refs.h
+++ b/refs.h
@@ -354,6 +354,14 @@ int refs_pack_refs(struct ref_store *refs, unsigned int flags);
 #define REF_NODEREF    0x01
 #define REF_FORCE_CREATE_REFLOG 0x40
 
+/*
+ * Flags that can be passed in to ref_transaction_update
+ */
+#define REF_TRANSACTION_UPDATE_ALLOWED_FLAGS \
+       REF_ISPRUNING |                      \
+       REF_FORCE_CREATE_REFLOG |            \
+       REF_NODEREF
+
 /*
  * Setup reflog before using. Fill in err and return -1 on failure.
  */