git/gpg-interface.c
Jeff King 076aa2cbda tempfile: auto-allocate tempfiles on heap
The previous commit taught the tempfile code to give up
ownership over tempfiles that have been renamed or deleted.
That makes it possible to use a stack variable like this:

  struct tempfile t;

  create_tempfile(&t, ...);
  ...
  if (!err)
          rename_tempfile(&t, ...);
  else
          delete_tempfile(&t);

But doing it this way has a high potential for creating
memory errors. The tempfile we pass to create_tempfile()
ends up on a global linked list, and it's not safe for it to
go out of scope until we've called one of those two
deactivation functions.

Imagine that we add an early return from the function that
forgets to call delete_tempfile(). With a static or heap
tempfile variable, the worst case is that the tempfile hangs
around until the program exits (and some functions like
setup_shallow_temporary rely on this intentionally, creating
a tempfile and then leaving it for later cleanup).

But with a stack variable as above, this is a serious memory
error: the variable goes out of scope and may be filled with
garbage by the time the tempfile code looks at it.  Let's
see if we can make it harder to get this wrong.

Since many callers need to allocate arbitrary numbers of
tempfiles, we can't rely on static storage as a general
solution. So we need to turn to the heap. We could just ask
all callers to pass us a heap variable, but that puts the
burden on them to call free() at the right time.

Instead, let's have the tempfile code handle the heap
allocation _and_ the deallocation (when the tempfile is
deactivated and removed from the list).

This changes the return value of all of the creation
functions. For the cleanup functions (delete and rename),
we'll add one extra bit of safety: instead of taking a
tempfile pointer, we'll take a pointer-to-pointer and set it
to NULL after freeing the object. This makes it safe to
double-call functions like delete_tempfile(), as the second
call treats the NULL input as a noop. Several callsites
follow this pattern.

The resulting patch does have a fair bit of noise, as each
caller needs to be converted to handle:

  1. Storing a pointer instead of the struct itself.

  2. Passing the pointer instead of taking the struct
     address.

  3. Handling a "struct tempfile *" return instead of a file
     descriptor.

We could play games to make this less noisy. For example, by
defining the tempfile like this:

  struct tempfile {
	struct heap_allocated_part_of_tempfile {
                int fd;
                ...etc
        } *actual_data;
  }

Callers would continue to have a "struct tempfile", and it
would be "active" only when the inner pointer was non-NULL.
But that just makes things more awkward in the long run.
There aren't that many callers, so we can simply bite
the bullet and adjust all of them. And the compiler makes it
easy for us to find them all.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2017-09-06 17:19:54 +09:00

242 lines
6.3 KiB
C

#include "cache.h"
#include "config.h"
#include "run-command.h"
#include "strbuf.h"
#include "gpg-interface.h"
#include "sigchain.h"
#include "tempfile.h"
static char *configured_signing_key;
static const char *gpg_program = "gpg";
#define PGP_SIGNATURE "-----BEGIN PGP SIGNATURE-----"
#define PGP_MESSAGE "-----BEGIN PGP MESSAGE-----"
void signature_check_clear(struct signature_check *sigc)
{
FREE_AND_NULL(sigc->payload);
FREE_AND_NULL(sigc->gpg_output);
FREE_AND_NULL(sigc->gpg_status);
FREE_AND_NULL(sigc->signer);
FREE_AND_NULL(sigc->key);
}
static struct {
char result;
const char *check;
} sigcheck_gpg_status[] = {
{ 'G', "\n[GNUPG:] GOODSIG " },
{ 'B', "\n[GNUPG:] BADSIG " },
{ 'U', "\n[GNUPG:] TRUST_NEVER" },
{ 'U', "\n[GNUPG:] TRUST_UNDEFINED" },
{ 'E', "\n[GNUPG:] ERRSIG "},
{ 'X', "\n[GNUPG:] EXPSIG "},
{ 'Y', "\n[GNUPG:] EXPKEYSIG "},
{ 'R', "\n[GNUPG:] REVKEYSIG "},
};
void parse_gpg_output(struct signature_check *sigc)
{
const char *buf = sigc->gpg_status;
int i;
/* Iterate over all search strings */
for (i = 0; i < ARRAY_SIZE(sigcheck_gpg_status); i++) {
const char *found, *next;
if (!skip_prefix(buf, sigcheck_gpg_status[i].check + 1, &found)) {
found = strstr(buf, sigcheck_gpg_status[i].check);
if (!found)
continue;
found += strlen(sigcheck_gpg_status[i].check);
}
sigc->result = sigcheck_gpg_status[i].result;
/* The trust messages are not followed by key/signer information */
if (sigc->result != 'U') {
sigc->key = xmemdupz(found, 16);
/* The ERRSIG message is not followed by signer information */
if (sigc-> result != 'E') {
found += 17;
next = strchrnul(found, '\n');
sigc->signer = xmemdupz(found, next - found);
}
}
}
}
int check_signature(const char *payload, size_t plen, const char *signature,
size_t slen, struct signature_check *sigc)
{
struct strbuf gpg_output = STRBUF_INIT;
struct strbuf gpg_status = STRBUF_INIT;
int status;
sigc->result = 'N';
status = verify_signed_buffer(payload, plen, signature, slen,
&gpg_output, &gpg_status);
if (status && !gpg_output.len)
goto out;
sigc->payload = xmemdupz(payload, plen);
sigc->gpg_output = strbuf_detach(&gpg_output, NULL);
sigc->gpg_status = strbuf_detach(&gpg_status, NULL);
parse_gpg_output(sigc);
out:
strbuf_release(&gpg_status);
strbuf_release(&gpg_output);
return sigc->result != 'G' && sigc->result != 'U';
}
void print_signature_buffer(const struct signature_check *sigc, unsigned flags)
{
const char *output = flags & GPG_VERIFY_RAW ?
sigc->gpg_status : sigc->gpg_output;
if (flags & GPG_VERIFY_VERBOSE && sigc->payload)
fputs(sigc->payload, stdout);
if (output)
fputs(output, stderr);
}
/*
* 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, unsigned long size)
{
char *eol;
size_t len = 0;
while (len < size && !starts_with(buf + len, PGP_SIGNATURE) &&
!starts_with(buf + len, PGP_MESSAGE)) {
eol = memchr(buf + len, '\n', size - len);
len += eol ? eol - (buf + len) + 1 : size - len;
}
return len;
}
void set_signing_key(const char *key)
{
free(configured_signing_key);
configured_signing_key = xstrdup(key);
}
int git_gpg_config(const char *var, const char *value, void *cb)
{
if (!strcmp(var, "user.signingkey")) {
set_signing_key(value);
}
if (!strcmp(var, "gpg.program")) {
if (!value)
return config_error_nonbool(var);
gpg_program = xstrdup(value);
}
return 0;
}
const char *get_signing_key(void)
{
if (configured_signing_key)
return configured_signing_key;
return git_committer_info(IDENT_STRICT|IDENT_NO_DATE);
}
/*
* 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)
{
struct child_process gpg = CHILD_PROCESS_INIT;
int ret;
size_t i, j, bottom;
struct strbuf gpg_status = STRBUF_INIT;
argv_array_pushl(&gpg.args,
gpg_program,
"--status-fd=2",
"-bsau", signing_key,
NULL);
bottom = signature->len;
/*
* When the username signingkey is bad, program could be terminated
* because gpg exits without reading and then write gets SIGPIPE.
*/
sigchain_push(SIGPIPE, SIG_IGN);
ret = pipe_command(&gpg, buffer->buf, buffer->len,
signature, 1024, &gpg_status, 0);
sigchain_pop(SIGPIPE);
ret |= !strstr(gpg_status.buf, "\n[GNUPG:] SIG_CREATED ");
strbuf_release(&gpg_status);
if (ret)
return error(_("gpg failed to sign the data"));
/* Strip CR from the line endings, in case we are on Windows. */
for (i = j = bottom; i < signature->len; i++)
if (signature->buf[i] != '\r') {
if (i != j)
signature->buf[j] = signature->buf[i];
j++;
}
strbuf_setlen(signature, j);
return 0;
}
/*
* Run "gpg" to see if the payload matches the detached signature.
* gpg_output, when set, receives the diagnostic output from GPG.
* gpg_status, when set, receives the status output from GPG.
*/
int verify_signed_buffer(const char *payload, size_t payload_size,
const char *signature, size_t signature_size,
struct strbuf *gpg_output, struct strbuf *gpg_status)
{
struct child_process gpg = CHILD_PROCESS_INIT;
struct tempfile *temp;
int ret;
struct strbuf buf = STRBUF_INIT;
temp = mks_tempfile_t(".git_vtag_tmpXXXXXX");
if (!temp)
return error_errno(_("could not create temporary file"));
if (write_in_full(temp->fd, signature, signature_size) < 0 ||
close_tempfile_gently(temp) < 0) {
error_errno(_("failed writing detached signature to '%s'"),
temp->filename.buf);
delete_tempfile(&temp);
return -1;
}
argv_array_pushl(&gpg.args,
gpg_program,
"--status-fd=1",
"--keyid-format=long",
"--verify", temp->filename.buf, "-",
NULL);
if (!gpg_status)
gpg_status = &buf;
sigchain_push(SIGPIPE, SIG_IGN);
ret = pipe_command(&gpg, payload, payload_size,
gpg_status, 0, gpg_output, 0);
sigchain_pop(SIGPIPE);
delete_tempfile(&temp);
ret |= !strstr(gpg_status->buf, "\n[GNUPG:] GOODSIG ");
strbuf_release(&buf); /* no matter it was used or not */
return ret;
}