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sesman: Prevent the use of 'alternate shell'

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By setting the new config value 'AllowAlternateShell' to 'no' it is now
possible to prevent the use of an alternate shell, which can be set by
the connecting user.
The default remains unchanged and any shell is allowed if the config
value is not specified. It can also be set explicitly to 'yes' to achieve
the same outcome.

Fixes: #850
This commit is contained in:
Lennart Sauerbeck 2023-04-14 20:22:42 +02:00
parent d7c3809ce8
commit d4ea314ac2
5 changed files with 53 additions and 13 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
docs/man/sesman.ini.5.in
View File

@ -283,6 +283,10 @@ To keep compatibility, the following aliases are also available.
If set to \fB1\fR, \fBtrue\fR or \fByes\fR, require group membership even
if the group specified in \fBTerminalServerUsers\fR doesn't exist.
.TP
\fBAllowAlternateShell\fR=\fI[true|false]\fR
If set to \fB0\fR, \fBfalse\fR or \fBno\fR, prevent usage of alternate shells by users.
.SH "X11 SERVER"
Following parameters can be used in the \fB[X11rdp]\fR, \fB[Xvnc]\fR and
\fB[Xorg]\fR sections.

7
sesman/config.c
View File

@ -212,6 +212,7 @@ config_read_security(int file, struct config_security *sc,
sc->ts_admins_enable = 0;
sc->restrict_outbound_clipboard = 0;
sc->restrict_inbound_clipboard = 0;
sc->allow_alternate_shell = 1;
file_read_section(file, SESMAN_CFG_SECURITY, param_n, param_v);
@ -279,6 +280,11 @@ config_read_security(int file, struct config_security *sc,
unrecognised);
}
}
if (0 == g_strcasecmp(buf, SESMAN_CFG_SEC_ALLOW_ALTERNATE_SHELL))
{
sc->allow_alternate_shell =
g_text2bool((char *)list_get_item(param_v, i));
}
}
@ -602,6 +608,7 @@ config_dump(struct config_sesman *config)
g_writeln(" AllowRootLogin: %d", sc->allow_root);
g_writeln(" MaxLoginRetry: %d", sc->login_retry);
g_writeln(" AlwaysGroupCheck: %d", sc->ts_always_group_check);
g_writeln(" AllowAlternateShell: %d", sc->allow_alternate_shell);
if (sc->restrict_outbound_clipboard == CLIP_RESTRICT_NONE)
{
g_writeln(" RestrictOutboundClipboard: %s", "none");

10
sesman/config.h
View File

@ -62,6 +62,7 @@
#define SESMAN_CFG_SEC_ALWAYSGROUPCHECK "AlwaysGroupCheck"
#define SESMAN_CFG_SEC_RESTRICT_OUTBOUND_CLIPBOARD "RestrictOutboundClipboard"
#define SESMAN_CFG_SEC_RESTRICT_INBOUND_CLIPBOARD "RestrictInboundClipboard"
#define SESMAN_CFG_SEC_ALLOW_ALTERNATE_SHELL "AllowAlternateShell"
#define SESMAN_CFG_SESSIONS "Sessions"
#define SESMAN_CFG_SESS_MAX "MaxSessions"
@ -141,6 +142,15 @@ struct config_security
* @brief if the clipboard should be enforced restricted. If true only allow server -> client, not vice versa.
*/
int restrict_inbound_clipboard;
/**
* @var allow_alternate_shell
* @brief allow an user-supplied alternate shell.
* @details 'YES' for all programs allowed, 'NO' for disabling of alternate
* shells.
* If not specified, 'YES' is assumed.
*/
int allow_alternate_shell;
};
/**

2
sesman/sesman.ini.in
View File

@ -37,6 +37,8 @@ RestrictOutboundClipboard=none
; false: an alias of none
; yes: an alias of all
RestrictInboundClipboard=none
; Set to 'no' to prevent users from logging in with alternate shells
#AllowAlternateShell=true
[Sessions]
;; X11DisplayOffset - x11 display number offset

43
sesman/session.c
View File

@ -596,30 +596,47 @@ session_start_fork(tbus data, tui8 type, struct SCP_SESSION *s)
if (x_server_running(display))
{
auth_set_env(data);
if (s->directory != 0)
if (s->directory != 0 && s->directory[0] != 0)
{
if (s->directory[0] != 0)
if (g_cfg->sec.allow_alternate_shell)
{
g_set_current_dir(s->directory);
}
else
{
LOG(LOG_LEVEL_WARNING,
"Directory change to %s requested, but not "
"allowed by AllowAlternateShell config value.",
s->directory);
}
}
if (s->program != 0 && s->program[0] != 0)
{
if (g_strchr(s->program, ' ') != 0 || g_strchr(s->program, '\t') != 0)
if (g_cfg->sec.allow_alternate_shell)
{
LOG(LOG_LEVEL_INFO,
"Starting user requested window manager on "
"display %d with embedded arguments using a shell: %s",
display, s->program);
const char *params[] = {"sh", "-c", s->program, NULL};
g_execvp("/bin/sh", (char **)params);
if (g_strchr(s->program, ' ') != 0 || g_strchr(s->program, '\t') != 0)
{
LOG(LOG_LEVEL_INFO,
"Starting user requested window manager on "
"display %d with embedded arguments using a shell: %s",
display, s->program);
const char *params[] = {"sh", "-c", s->program, NULL};
g_execvp("/bin/sh", (char **)params);
}
else
{
LOG(LOG_LEVEL_INFO,
"Starting user requested window manager on "
"display %d: %s", display, s->program);
g_execlp3(s->program, s->program, 0);
}
}
else
{
LOG(LOG_LEVEL_INFO,
"Starting user requested window manager on "
"display %d: %s", display, s->program);
g_execlp3(s->program, s->program, 0);
LOG(LOG_LEVEL_WARNING,
"Shell %s requested by user, but not allowed by "
"AllowAlternateShell config value.",
s->program);
}
}
else