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gpg: Detect race between pubring.gpg and pubring.kbx use.

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* g10/keydb.c (maybe_create_keyring_or_box): Detect race condition.

Signed-off-by: Werner Koch <wk@gnupg.org>
This commit is contained in:
Werner Koch 2016-01-14 18:29:26 +01:00
parent 8241ed59d0
commit 3b1248e007
No known key found for this signature in database
GPG Key ID: E3FDFF218E45B72B
1 changed files with 32 additions and 0 deletions
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32
g10/keydb.c
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@ -272,6 +272,8 @@ maybe_create_keyring_or_box (char *filename, int is_box, int force_create)
int rc; int rc;
mode_t oldmask; mode_t oldmask;
char *last_slash_in_filename; char *last_slash_in_filename;
char *bak_fname = NULL;
char *tmp_fname = NULL;
int save_slash; int save_slash;
/* A quick test whether the filename already exists. */ /* A quick test whether the filename already exists. */
@ -350,11 +352,39 @@ maybe_create_keyring_or_box (char *filename, int is_box, int force_create)
} }
/* Now the real test while we are locked. */ /* Now the real test while we are locked. */
/* Gpg either uses pubring.gpg or pubring.kbx and thus different
* lock files. Now, when one gpg process is updating a pubring.gpg
* and thus holding the corresponding lock, a second gpg process may
* get to here at the time between the two rename operation used by
* the first process to update pubring.gpg. The lock taken above
* may not protect the second process if it tries to create a
* pubring.kbx file which would be protected by a different lock
* file.
*
* We can detect this case by checking that the two temporary files
* used by the update code exist at the same time. In that case we
* do not create a new file but act as if FORCE_CREATE has not been
* given. Obviously there is a race between our two checks but the
* worst thing is that we won't create a new file, which is better
* than to accidentally creating one. */
rc = keybox_tmp_names (filename, is_box, &bak_fname, &tmp_fname);
if (rc)
goto leave;
if (!access (filename, F_OK)) if (!access (filename, F_OK))
{ {
rc = 0; /* Okay, we may access the file now. */ rc = 0; /* Okay, we may access the file now. */
goto leave; goto leave;
} }
if (!access (bak_fname, F_OK) && !access (tmp_fname, F_OK))
{
/* Very likely another process is updating a pubring.gpg and we
should not create a pubring.kbx. */
rc = gpg_error (GPG_ERR_ENOENT);
goto leave;
}
/* The file does not yet exist, create it now. */ /* The file does not yet exist, create it now. */
oldmask = umask (077); oldmask = umask (077);
@ -422,6 +452,8 @@ maybe_create_keyring_or_box (char *filename, int is_box, int force_create)
dotlock_release (lockhd); dotlock_release (lockhd);
dotlock_destroy (lockhd); dotlock_destroy (lockhd);
} }
xfree (bak_fname);
xfree (tmp_fname);
return rc; return rc;
} }