* [bug: login] login command with -f flag fails to switch user account.
@ 2018-06-13 17:01 Takashi Yano
2018-06-17 6:22 ` Takashi Yano
0 siblings, 1 reply; 6+ messages in thread
From: Takashi Yano @ 2018-06-13 17:01 UTC (permalink / raw)
To: cygwin
Hi,
I have found the login command with -f flag fails to switch
user account correctly.
This causes a severe security problem. User can get console
having cyg_server rights without password by following steps.
Prepare:
0.1. Install rsh-sever and rsh with inetutils packages.
0.2. Set them up to work properly.
Steps:
1.1. Make ~/.rhosts with line 'localhost'
1.2. Execute 'rlogin localhost'.
Now you can get the cyg_server rights.
This is caused by bug of login command. With the settings
above, rlogind is executed as cyg_server account. If .rhosts
is valid, rlogind executes login command with -f flag.
This should switch the user account to the user specified.
However, login command fails to switch the account.
As a result, shell is executed as cyg_server account
instead of specified user account.
I looked into this problem, and found the bug is in login.c.
The account information of targeted user is set to a pointer:
struct passwd *pwd;
by calling getpwnam(username).
This pointer points the system static area. This area is
overwritten with the account information of current user,
i.e. cyg_server, by calling getpwuid(uid) in isROOT_UID().
getpwnam() and getpwuid() seems to share the same system area.
login calls setuid(pwd->pw_uid) and setgid(pwd->pw_gid) to
switch the account, however area pointed by pwd is already
overwritten to the information of current user.
As a result, the account switching is done to the same user
account (cyg_server) though it should be done to the account
specified.
Above is the mechanism of this bug.
--
Takashi Yano <takashi.yano@nifty.ne.jp>
--
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* Re: [bug: login] login command with -f flag fails to switch user account.
2018-06-13 17:01 [bug: login] login command with -f flag fails to switch user account Takashi Yano
@ 2018-06-17 6:22 ` Takashi Yano
2018-06-17 22:31 ` Takashi Yano
0 siblings, 1 reply; 6+ messages in thread
From: Takashi Yano @ 2018-06-17 6:22 UTC (permalink / raw)
To: cygwin
[-- Attachment #1: Type: text/plain, Size: 167 bytes --]
Hi Corinna and Yaakov,
I have created a patch against the git head to solve this problem.
Could you please have a look?
--
Takashi Yano <takashi.yano@nifty.ne.jp>
[-- Attachment #2: 0001-Fixed-the-failure-in-the-case-of-trying-to-switch-us.patch --]
[-- Type: application/octet-stream, Size: 2314 bytes --]
From b070bb0f9ced001d3fee40a75a4882ff17d02428 Mon Sep 17 00:00:00 2001
From: Takashi Yano <takashi.yano@nifty.ne.jp>
Date: Sat, 16 Jun 2018 21:59:30 +0900
Subject: [PATCH] Fixed the failure in the case of trying to switch user
account with F flag.
* login.c (main): Use getpwnam_r() instead of getpwnam() to prevent
overwriting the area pointed by pwd by other calls of getpw* family
functions.
* login.c (isROOT_UID): Remove checking SeIncreaseQuotaPrivilege
privilege because account cyg_server created by csih does not have
this privilege.
* winsec.c (getUserInfoForUID): Fix the first argument of the second
NetUserGetInfo() call so that it can check user information locally
if the machine is on a domain.
---
login.c | 9 +++++----
winsec.c | 3 +--
2 files changed, 6 insertions(+), 6 deletions(-)
diff --git a/login.c b/login.c
index 2ddfdcd..271d5e8 100644
--- a/login.c
+++ b/login.c
@@ -91,6 +91,8 @@ static void sleepexit (int eval);
*/
int timeout = 300;
+struct passwd userpwd;
+char pwbuf[16384];
struct passwd *pwd;
int failures;
char term[64], *hostname, *username, *tty;
@@ -213,7 +215,7 @@ main (int argc, char **argv)
}
(void) strcpy (tbuf, username);
#ifdef __CYGWIN__
- pwd = getpwnam (username);
+ getpwnam_r (username, &userpwd, pwbuf, sizeof(pwbuf), &pwd);
#else
if (pwd = getpwnam (username))
salt = pwd->pw_passwd;
@@ -551,10 +553,9 @@ isROOT_UID (uid_t uid)
{
static const char *REQUIRED_PRIVS[] = {
"SeAssignPrimaryTokenPrivilege",
- "SeTcbPrivilege",
- "SeIncreaseQuotaPrivilege"
+ "SeTcbPrivilege"
};
- static const ULONG NUM_REQUIRED_PRIV = 3;
+ static const ULONG NUM_REQUIRED_PRIV = 2;
OSVERSIONINFOEX osvi;
struct passwd *pw;
diff --git a/winsec.c b/winsec.c
index 307a66b..13c5ecf 100644
--- a/winsec.c
+++ b/winsec.c
@@ -978,8 +978,7 @@ getUserInfoForUID (uid_t uid,
/* if we had a domain, then try again locally. if we didn't have a
domain, then the initial call WAS local */
if (NetUserGetInfo
- (*uni_servername, (LPWSTR) & uni_name, level,
- bufptr) != NERR_Success)
+ (NULL, (LPWSTR) & uni_name, level, bufptr) != NERR_Success)
{
syslog (LOG_ERR,
"unable to obtain user info for %s [tried domain controller %s and localhost]\n",
--
2.17.0
[-- Attachment #3: Type: text/plain, Size: 219 bytes --]
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^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [bug: login] login command with -f flag fails to switch user account.
2018-06-17 6:22 ` Takashi Yano
@ 2018-06-17 22:31 ` Takashi Yano
2018-06-17 22:31 ` Takashi Yano
0 siblings, 1 reply; 6+ messages in thread
From: Takashi Yano @ 2018-06-17 22:31 UTC (permalink / raw)
To: cygwin
[-- Attachment #1: Type: text/plain, Size: 270 bytes --]
Hi Corinna and Yaakov,
On Sun, 17 Jun 2018 10:13:13 +0900
Takashi Yano wrote:
> I have created a patch against the git head to solve this problem.
> Could you please have a look?
Fix typo and wording in commitment message.
--
Takashi Yano <takashi.yano@nifty.ne.jp>
[-- Attachment #2: 0001-Fix-the-issue-that-login-command-with-f-flag-fails-t.patch --]
[-- Type: application/octet-stream, Size: 2416 bytes --]
From be7acbe15e81af2f4c65878644fff593e5b1294c Mon Sep 17 00:00:00 2001
From: Takashi Yano <takashi.yano@nifty.ne.jp>
Date: Sat, 16 Jun 2018 21:59:30 +0900
Subject: [PATCH] Fix the issue that login command with -f flag fails to switch
user account.
* login.c (main): Use getpwnam_r() instead of getpwnam() to prevent
the area pointed by pwd being overwritten by other calls of getpw*
family functions.
* login.c (isROOT_UID): Remove checking SeIncreaseQuotaPrivilege
privilege because the account cyg_server created by csih does not
have this privilege.
* winsec.c (getUserInfoForUID): Fix the first argument of the second
NetUserGetInfo() call so that it can check user information locally
if the machine is on a domain.
Refer to the following post for detail.
https://cygwin.com/ml/cygwin/2018-06/msg00146.html
---
login.c | 9 +++++----
winsec.c | 3 +--
2 files changed, 6 insertions(+), 6 deletions(-)
diff --git a/login.c b/login.c
index 2ddfdcd..271d5e8 100644
--- a/login.c
+++ b/login.c
@@ -91,6 +91,8 @@ static void sleepexit (int eval);
*/
int timeout = 300;
+struct passwd userpwd;
+char pwbuf[16384];
struct passwd *pwd;
int failures;
char term[64], *hostname, *username, *tty;
@@ -213,7 +215,7 @@ main (int argc, char **argv)
}
(void) strcpy (tbuf, username);
#ifdef __CYGWIN__
- pwd = getpwnam (username);
+ getpwnam_r (username, &userpwd, pwbuf, sizeof(pwbuf), &pwd);
#else
if (pwd = getpwnam (username))
salt = pwd->pw_passwd;
@@ -551,10 +553,9 @@ isROOT_UID (uid_t uid)
{
static const char *REQUIRED_PRIVS[] = {
"SeAssignPrimaryTokenPrivilege",
- "SeTcbPrivilege",
- "SeIncreaseQuotaPrivilege"
+ "SeTcbPrivilege"
};
- static const ULONG NUM_REQUIRED_PRIV = 3;
+ static const ULONG NUM_REQUIRED_PRIV = 2;
OSVERSIONINFOEX osvi;
struct passwd *pw;
diff --git a/winsec.c b/winsec.c
index 307a66b..13c5ecf 100644
--- a/winsec.c
+++ b/winsec.c
@@ -978,8 +978,7 @@ getUserInfoForUID (uid_t uid,
/* if we had a domain, then try again locally. if we didn't have a
domain, then the initial call WAS local */
if (NetUserGetInfo
- (*uni_servername, (LPWSTR) & uni_name, level,
- bufptr) != NERR_Success)
+ (NULL, (LPWSTR) & uni_name, level, bufptr) != NERR_Success)
{
syslog (LOG_ERR,
"unable to obtain user info for %s [tried domain controller %s and localhost]\n",
--
2.17.0
[-- Attachment #3: Type: text/plain, Size: 219 bytes --]
--
Problem reports: http://cygwin.com/problems.html
FAQ: http://cygwin.com/faq/
Documentation: http://cygwin.com/docs.html
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^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [bug: login] login command with -f flag fails to switch user account.
2018-06-17 22:31 ` Takashi Yano
@ 2018-06-17 22:31 ` Takashi Yano
2018-06-18 14:48 ` Corinna Vinschen
0 siblings, 1 reply; 6+ messages in thread
From: Takashi Yano @ 2018-06-17 22:31 UTC (permalink / raw)
To: cygwin
[-- Attachment #1: Type: text/plain, Size: 194 bytes --]
On Sun, 17 Jun 2018 11:14:33 +0900
Takashi Yano <takashi.yano@nifty.ne.jp> wrote:
> Fix typo and wording in commitment message.
Fixed again. Sorry.
--
Takashi Yano <takashi.yano@nifty.ne.jp>
[-- Attachment #2: 0001-Fix-the-issue-that-login-command-with-f-flag-fails-t.patch --]
[-- Type: application/octet-stream, Size: 2426 bytes --]
From b8669c90e017e0b6481cb1ebaa8e9be321fcc0aa Mon Sep 17 00:00:00 2001
From: Takashi Yano <takashi.yano@nifty.ne.jp>
Date: Sat, 16 Jun 2018 21:59:30 +0900
Subject: [PATCH] Fix the issue that login command with -f flag fails to switch
user account.
* login.c (main): Use getpwnam_r() instead of getpwnam() to prevent
the area pointed to by pwd from being overwritten by other calls of
getpw*() family functions.
* login.c (isROOT_UID): Remove checking SeIncreaseQuotaPrivilege
privilege because the account cyg_server created by csih does not
have this privilege.
* winsec.c (getUserInfoForUID): Fix the first argument of the second
NetUserGetInfo() call so that it can check user information locally
if the machine is on a domain.
Refer to the following post for detail.
https://cygwin.com/ml/cygwin/2018-06/msg00146.html
---
login.c | 9 +++++----
winsec.c | 3 +--
2 files changed, 6 insertions(+), 6 deletions(-)
diff --git a/login.c b/login.c
index 2ddfdcd..271d5e8 100644
--- a/login.c
+++ b/login.c
@@ -91,6 +91,8 @@ static void sleepexit (int eval);
*/
int timeout = 300;
+struct passwd userpwd;
+char pwbuf[16384];
struct passwd *pwd;
int failures;
char term[64], *hostname, *username, *tty;
@@ -213,7 +215,7 @@ main (int argc, char **argv)
}
(void) strcpy (tbuf, username);
#ifdef __CYGWIN__
- pwd = getpwnam (username);
+ getpwnam_r (username, &userpwd, pwbuf, sizeof(pwbuf), &pwd);
#else
if (pwd = getpwnam (username))
salt = pwd->pw_passwd;
@@ -551,10 +553,9 @@ isROOT_UID (uid_t uid)
{
static const char *REQUIRED_PRIVS[] = {
"SeAssignPrimaryTokenPrivilege",
- "SeTcbPrivilege",
- "SeIncreaseQuotaPrivilege"
+ "SeTcbPrivilege"
};
- static const ULONG NUM_REQUIRED_PRIV = 3;
+ static const ULONG NUM_REQUIRED_PRIV = 2;
OSVERSIONINFOEX osvi;
struct passwd *pw;
diff --git a/winsec.c b/winsec.c
index 307a66b..13c5ecf 100644
--- a/winsec.c
+++ b/winsec.c
@@ -978,8 +978,7 @@ getUserInfoForUID (uid_t uid,
/* if we had a domain, then try again locally. if we didn't have a
domain, then the initial call WAS local */
if (NetUserGetInfo
- (*uni_servername, (LPWSTR) & uni_name, level,
- bufptr) != NERR_Success)
+ (NULL, (LPWSTR) & uni_name, level, bufptr) != NERR_Success)
{
syslog (LOG_ERR,
"unable to obtain user info for %s [tried domain controller %s and localhost]\n",
--
2.17.0
[-- Attachment #3: Type: text/plain, Size: 219 bytes --]
--
Problem reports: http://cygwin.com/problems.html
FAQ: http://cygwin.com/faq/
Documentation: http://cygwin.com/docs.html
Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [bug: login] login command with -f flag fails to switch user account.
2018-06-17 22:31 ` Takashi Yano
@ 2018-06-18 14:48 ` Corinna Vinschen
2018-06-19 2:50 ` Yaakov Selkowitz
0 siblings, 1 reply; 6+ messages in thread
From: Corinna Vinschen @ 2018-06-18 14:48 UTC (permalink / raw)
To: cygwin; +Cc: Yaakov Selkowitz
[-- Attachment #1: Type: text/plain, Size: 620 bytes --]
On Jun 17 12:42, Takashi Yano wrote:
> On Sun, 17 Jun 2018 11:14:33 +0900
> Takashi Yano <takashi.yano@nifty.ne.jp> wrote:
> > Fix typo and wording in commitment message.
>
> Fixed again. Sorry.
No worries. Thanks for the patch, I pushed it.
Yaakov, would you mind to rebuild the login package? I'm not sure what
to do with this meson stuff. I have a local build using the standard
method, though. If that's ok I just upload it.
Thanks,
Corinna
--
Corinna Vinschen Please, send mails regarding Cygwin to
Cygwin Maintainer cygwin AT cygwin DOT com
Red Hat
[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [bug: login] login command with -f flag fails to switch user account.
2018-06-18 14:48 ` Corinna Vinschen
@ 2018-06-19 2:50 ` Yaakov Selkowitz
0 siblings, 0 replies; 6+ messages in thread
From: Yaakov Selkowitz @ 2018-06-19 2:50 UTC (permalink / raw)
To: cygwin
On 2018-06-18 07:17, Corinna Vinschen wrote:
> On Jun 17 12:42, Takashi Yano wrote:
>> On Sun, 17 Jun 2018 11:14:33 +0900
>> Takashi Yano <takashi.yano@nifty.ne.jp> wrote:
>>> Fix typo and wording in commitment message.
>>
>> Fixed again. Sorry.
>
> No worries. Thanks for the patch, I pushed it.
>
> Yaakov, would you mind to rebuild the login package? I'm not sure what
> to do with this meson stuff. I have a local build using the standard
> method, though. If that's ok I just upload it.
That should be fine, go ahead.
--
Yaakov
--
Problem reports: http://cygwin.com/problems.html
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end of thread, other threads:[~2018-06-18 14:48 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
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2018-06-13 17:01 [bug: login] login command with -f flag fails to switch user account Takashi Yano
2018-06-17 6:22 ` Takashi Yano
2018-06-17 22:31 ` Takashi Yano
2018-06-17 22:31 ` Takashi Yano
2018-06-18 14:48 ` Corinna Vinschen
2018-06-19 2:50 ` Yaakov Selkowitz
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