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security: Inhibit execution of privilege escalating functions

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This patch allows individual dialplan functions to be marked as
'dangerous', to inhibit their execution from external sources.

A 'dangerous' function is one which results in a privilege escalation.
For example, if one were to read the channel variable SHELL(rm -rf /)
Bad Things(TM) could happen; even if the external source has only read
permissions.

Execution from external sources may be enabled by setting
'live_dangerously' to 'yes' in the [options] section of asterisk.conf.
Although doing so is not recommended.

Also, the ABI was changed to something more reasonable, since Asterisk
12 does not yet have a public release.

(closes issue ASTERISK-22905)
Review: http://reviewboard.digium.internal/r/432/
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Merged revisions 403913 from http://svn.asterisk.org/svn/asterisk/branches/1.8
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Merged revisions 403917 from http://svn.asterisk.org/svn/asterisk/branches/11
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Merged revisions 403959 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@403960 65c4cc65-6c06-0410-ace0-fbb531ad65f3
This commit is contained in:
David M. Lee
2013-12-16 19:11:51 +00:00
parent 00dcee2a64
commit 744556c01d
12 changed files with 418 additions and 37 deletions
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21
funcs/func_lock.c
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@@ -59,6 +59,11 @@ ASTERISK_FILE_VERSION(__FILE__, "$Revision$")
Returns <literal>1</literal> if the lock was obtained or <literal>0</literal> on error.</para>
<note><para>To avoid the possibility of a deadlock, LOCK will only attempt to
obtain the lock for 3 seconds if the channel already has another lock.</para></note>
<note>
<para>If <literal>live_dangerously</literal> in <literal>asterisk.conf</literal>
is set to <literal>no</literal>, this function can only be executed from the
dialplan, and not directly from external protocols.</para>
</note>
</description>
</function>
<function name="TRYLOCK" language="en_US">
@@ -72,6 +77,11 @@ ASTERISK_FILE_VERSION(__FILE__, "$Revision$")
<para>Attempts to grab a named lock exclusively, and prevents other channels
from obtaining the same lock. Returns <literal>1</literal> if the lock was
available or <literal>0</literal> otherwise.</para>
<note>
<para>If <literal>live_dangerously</literal> in <literal>asterisk.conf</literal>
is set to <literal>no</literal>, this function can only be executed from the
dialplan, and not directly from external protocols.</para>
</note>
</description>
</function>
<function name="UNLOCK" language="en_US">
@@ -86,6 +96,11 @@ ASTERISK_FILE_VERSION(__FILE__, "$Revision$")
had a lock or <literal>0</literal> otherwise.</para>
<note><para>It is generally unnecessary to unlock in a hangup routine, as any locks
held are automatically freed when the channel is destroyed.</para></note>
<note>
<para>If <literal>live_dangerously</literal> in <literal>asterisk.conf</literal>
is set to <literal>no</literal>, this function can only be executed from the
dialplan, and not directly from external protocols.</para>
</note>
</description>
</function>
***/
@@ -502,9 +517,9 @@ static int unload_module(void)
static int load_module(void)
{
int res = ast_custom_function_register(&lock_function);
res |= ast_custom_function_register(&trylock_function);
res |= ast_custom_function_register(&unlock_function);
int res = ast_custom_function_register_escalating(&lock_function, AST_CFE_READ);
res |= ast_custom_function_register_escalating(&trylock_function, AST_CFE_READ);
res |= ast_custom_function_register_escalating(&unlock_function, AST_CFE_READ);
if (ast_pthread_create_background(&broker_tid, NULL, lock_broker, NULL)) {
ast_log(LOG_ERROR, "Failed to start lock broker thread. Unloading func_lock module.\n");