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Use a temporary file to ensure we always have a challenge

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If we use ftruncate we might end up in the situation that we do not
have a challenge on disk, leading to the user being unable to log in.
By using a temporary file, fsync and rename we avoid this problem.
This commit is contained in:
Tollef Fog Heen 2011-03-16 22:44:25 +01:00
parent dc6cd95a98
commit 1364b39db7
1 changed files with 29 additions and 5 deletions
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34
pam_yubico.c
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@ -446,7 +446,7 @@ get_user_challenge_file(struct cfg *cfg, const char *username, char **fn)
static int
do_challenge_response(struct cfg *cfg, const char *username)
{
char *userfile = NULL;
char *userfile = NULL, *tmpfile = NULL;
FILE *f = NULL;
char challenge_hex[64], expected_response[64];
char challenge[32];
@ -472,7 +472,7 @@ do_challenge_response(struct cfg *cfg, const char *username)
D(("Loading challenge from file %s", userfile));
/* XXX should drop root privileges before opening file in user's home directory */
f = fopen(userfile, "r+");
f = fopen(userfile, "r");
if (! f)
goto out;
r = fscanf(f, "%63[0-9a-z]:%63[0-9a-z]:%d", &challenge_hex, &expected_response, &slot);
@ -529,15 +529,38 @@ do_challenge_response(struct cfg *cfg, const char *username)
errno = 0;
yubikey_hex_encode(response_hex, (char *)response, response_len > 20 ? 20 : response_len);
rewind(f);
/* Write out the new file */
if (fclose(f) < 0) {
f = NULL;
goto out;
}
tmpfile = malloc(strlen(userfile) + 1 + 4);
if (! tmpfile)
goto out;
strcpy(tmpfile, userfile);
strcat(tmpfile, ".tmp");
f = fopen(tmpfile, "w");
if (! f)
goto out;
fd = fileno(f);
if (fd == -1)
goto out;
if (ftruncate(fd, 0))
goto out;
fprintf(f, "%s:%s:%d\n", challenge_hex, response_hex, slot);
if (fflush(f) < 0)
goto out;
if (fsync(fd) < 0)
goto out;
if (fclose(f) < 0) {
f = NULL;
goto out;
}
f = NULL;
if (rename(tmpfile, userfile) < 0) {
goto out;
}
D(("Challenge-response success!"));
@ -562,6 +585,7 @@ do_challenge_response(struct cfg *cfg, const char *username)
fclose(f);
free(userfile);
free(tmpfile);
return ret;
}
#undef USERFILE