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Subject: [libssh2] #244: scp_send may transmit not initialised memory

[libssh2] #244: scp_send may transmit not initialised memory

From: libssh2 Trac <trac_at_libssh2.stuge.se>
Date: Tue, 10 Jul 2012 16:15:36 -0000

#244: scp_send may transmit not initialised memory
--------------------------+--------------------
 Reporter: torsten.rupp | Owner:
     Type: defect | Status: new
 Priority: normal | Milestone: 1.4.0
Component: SCP | Version: 1.4.1
 Keywords: scp_send | Blocked By:
   Blocks: |
--------------------------+--------------------
 In the function scp_send() the transmission function
 _libssh2_channel_process_startup() may be called with a message size
 larger than the actual initialised message buffer. This cause with e. g.
 valgrind a warning that not initialised memory is used.

 From my analysis this is the problem:

 - at the beginning of then function scp_send() (line 787, scp.c)
 _libssh2_shell_quotedsize() is called to detect the memory space needed
 for session->scpRecv_command. This size is the _maximum_ size of the
 encoded message.

         session->scpSend_command_len =
             _libssh2_shell_quotedsize(path) + sizeof("scp -t ") +
             ((mtime || atime)?1:0);

 - the memory is allocated (line 791, scp.c)

 - the message content is formated with a snprintf()-call (line 799, scp.c)

         snprintf((char *)session->scpSend_command,
 session->scpSend_command_len,
                  "scp -%st ", (mtime || atime)?"p":"");

 - the length of the resulting string is calculate (line 802, scp.c)

         cmd_len = strlen((char *)session->scpSend_command);

 - the path parameter is added with possible quotes (line 804, scp.c)

         (void)shell_quotearg(path,
                              &session->scpSend_command[cmd_len],
                              session->scpSend_command_len - cmd_len);

 - the command is terminated with NUL character, but not necessarily at the
 right place. The quoted path string may be shorter than the previously
 calculated max. length (line 808, scp.c)

         session->scpSend_command[session->scpSend_command_len - 1] = '\0';

 - the formated message is send with the _maximum_ length, not the actual
 length (line 842, scp.c)

         rc = _libssh2_channel_process_startup(session->scpSend_channel,
 "exec",
                                               sizeof("exec") - 1,
                                               (char *)
 session->scpSend_command,
 session->scpSend_command_len);

 This cause that the called transmission function access not initialised
 memory. This may not harm as long as the receiver will respect the
 terminating NUL character in the message. But at least more data then
 necessary is transmitted (path plus some random data) and checking tools
 like e. g. valgrind report a warning.

-- 
Ticket URL: <http://trac.libssh2.org/ticket/244>
libssh2 <http://trac.libssh2.org/>
C library for writing portable SSH2 clients
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Received on 2012-07-10

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