git/gpg-interface.h
Hans Jerry Illikainen 72b006f4bf gpg-interface: prefer check_signature() for GPG verification
This commit refactors the use of verify_signed_buffer() outside of
gpg-interface.c to use check_signature() instead.  It also turns
verify_signed_buffer() into a file-local function since it's now only
invoked internally by check_signature().

There were previously two globally scoped functions used in different
parts of Git to perform GPG signature verification:
verify_signed_buffer() and check_signature().  Now only
check_signature() is used.

The verify_signed_buffer() function doesn't guard against duplicate
signatures as described by Michał Górny [1].  Instead it only ensures a
non-erroneous exit code from GPG and the presence of at least one
GOODSIG status field.  This stands in contrast with check_signature()
that returns an error if more than one signature is encountered.

The lower degree of verification makes the use of verify_signed_buffer()
problematic if callers don't parse and validate the various parts of the
GPG status message themselves.  And processing these messages seems like
a task that should be reserved to gpg-interface.c with the function
check_signature().

Furthermore, the use of verify_signed_buffer() makes it difficult to
introduce new functionality that relies on the content of the GPG status
lines.

Now all operations that does signature verification share a single entry
point to gpg-interface.c.  This makes it easier to propagate changed or
additional functionality in GPG signature verification to all parts of
Git, without having odd edge-cases that don't perform the same degree of
verification.

[1] https://dev.gentoo.org/~mgorny/articles/attack-on-git-signature-verification.html

Signed-off-by: Hans Jerry Illikainen <hji@dyntopia.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2019-11-30 13:52:35 -08:00

58 lines
1.5 KiB
C

#ifndef GPG_INTERFACE_H
#define GPG_INTERFACE_H
struct strbuf;
#define GPG_VERIFY_VERBOSE 1
#define GPG_VERIFY_RAW 2
#define GPG_VERIFY_OMIT_STATUS 4
struct signature_check {
char *payload;
char *gpg_output;
char *gpg_status;
/*
* possible "result":
* 0 (not checked)
* N (checked but no further result)
* U (untrusted good)
* G (good)
* B (bad)
*/
char result;
char *signer;
char *key;
char *fingerprint;
char *primary_key_fingerprint;
};
void signature_check_clear(struct signature_check *sigc);
/*
* Look at GPG signed content (e.g. a signed tag object), whose
* payload is followed by a detached signature on it. Return the
* offset where the embedded detached signature begins, or the end of
* the data when there is no such signature.
*/
size_t parse_signature(const char *buf, size_t size);
/*
* Create a detached signature for the contents of "buffer" and append
* it after "signature"; "buffer" and "signature" can be the same
* strbuf instance, which would cause the detached signature appended
* at the end.
*/
int sign_buffer(struct strbuf *buffer, struct strbuf *signature,
const char *signing_key);
int git_gpg_config(const char *, const char *, void *);
void set_signing_key(const char *);
const char *get_signing_key(void);
int check_signature(const char *payload, size_t plen,
const char *signature, size_t slen,
struct signature_check *sigc);
void print_signature_buffer(const struct signature_check *sigc,
unsigned flags);
#endif