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emacsclient: fix symlink/socket race

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* lib-src/emacsclient.c (socket_status): New arg UID.
All uses changed.
(set_local_socket): Don’t create the unbound socket unless the
initial sanity checks on the socket file succeed; this
simplifies cleaning it up.  Check socket ownership again
after connecting, to fix a race (Bug#33366).
This commit is contained in:
Paul Eggert 2018-12-02 22:32:28 -08:00
parent e5634aae53
commit 3e5d775545
1 changed files with 41 additions and 37 deletions
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78
lib-src/emacsclient.c
View file

@ -1079,20 +1079,21 @@ find_tty (const char **tty_type, const char **tty_name, bool noabort)
#ifdef SOCKETS_IN_FILE_SYSTEM
/* Three possibilities:
/* Return the file status of NAME, ordinarily a socket.
It should be owned by UID. Return one of the following:
>0 - 'stat' failed with this errno value
-1 - isn't owned by us
0 - success: none of the above */
static int
socket_status (const char *name)
socket_status (const char *name, uid_t uid)
{
struct stat statbfr;
if (stat (name, &statbfr) != 0)
return errno;
if (statbfr.st_uid != geteuid ())
if (statbfr.st_uid != uid)
return -1;
return 0;
@ -1316,18 +1317,11 @@ set_local_socket (char const *server_name)
struct sockaddr_un un;
struct sockaddr sa;
} server = {{ .sun_family = AF_UNIX }};
HSOCKET s = socket (AF_UNIX, SOCK_STREAM, 0);
if (s < 0)
{
message (true, "%s: socket: %s\n", progname, strerror (errno));
return INVALID_SOCKET;
}
char *sockname = server.un.sun_path;
enum { socknamesize = sizeof server.un.sun_path };
int tmpdirlen = -1;
int socknamelen = -1;
uid_t uid = geteuid ();
if (strchr (server_name, '/')
|| (ISSLASH ('\\') && strchr (server_name, '\\')))
@ -1359,7 +1353,7 @@ set_local_socket (char const *server_name)
tmpdirlen = snprintf (sockname, socknamesize, "/tmp");
}
socknamelen = local_sockname (sockname, socknamesize, tmpdirlen,
geteuid (), server_name);
uid, server_name);
}
}
@ -1370,7 +1364,7 @@ set_local_socket (char const *server_name)
}
/* See if the socket exists, and if it's owned by us. */
int sock_status = socket_status (sockname);
int sock_status = socket_status (sockname, uid);
if (sock_status)
{
/* Failing that, see if LOGNAME or USER exist and differ from
@ -1387,7 +1381,7 @@ set_local_socket (char const *server_name)
{
struct passwd *pw = getpwnam (user_name);
if (pw && (pw->pw_uid != geteuid ()))
if (pw && pw->pw_uid != uid)
{
/* We're running under su, apparently. */
socknamelen = local_sockname (sockname, socknamesize, tmpdirlen,
@ -1399,39 +1393,49 @@ set_local_socket (char const *server_name)
exit (EXIT_FAILURE);
}
sock_status = socket_status (sockname);
sock_status = socket_status (sockname, uid);
}
}
}
switch (sock_status)
if (sock_status == 0)
{
case -1:
/* There's a socket, but it isn't owned by us. */
message (true, "%s: Invalid socket owner\n", progname);
break;
HSOCKET s = socket (AF_UNIX, SOCK_STREAM, 0);
if (s < 0)
{
message (true, "%s: socket: %s\n", progname, strerror (errno));
return INVALID_SOCKET;
}
if (connect (s, &server.sa, sizeof server.un) != 0)
{
message (true, "%s: connect: %s\n", progname, strerror (errno));
CLOSE_SOCKET (s);
return INVALID_SOCKET;
}
case 0:
if (connect (s, &server.sa, sizeof server.un) == 0)
struct stat connect_stat;
if (fstat (s, &connect_stat) != 0)
sock_status = errno;
else if (connect_stat.st_uid == uid)
return s;
message (true, "%s: connect: %s\n", progname, strerror (errno));
break;
default:
/* 'stat' failed. */
if (sock_status == ENOENT)
message (true,
("%s: can't find socket; have you started the server?\n"
"%s: To start the server in Emacs,"
" type \"M-x server-start\".\n"),
progname, progname);
else
message (true, "%s: can't stat %s: %s\n",
progname, sockname, strerror (sock_status));
break;
sock_status = -1;
CLOSE_SOCKET (s);
}
CLOSE_SOCKET (s);
if (sock_status < 0)
message (true, "%s: Invalid socket owner\n", progname);
else if (sock_status == ENOENT)
message (true,
("%s: can't find socket; have you started the server?\n"
"%s: To start the server in Emacs,"
" type \"M-x server-start\".\n"),
progname, progname);
else
message (true, "%s: can't stat %s: %s\n",
progname, sockname, strerror (sock_status));
return INVALID_SOCKET;
}
#endif /* SOCKETS_IN_FILE_SYSTEM */