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Prevent TOCTTOU bugs in C ports

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* libguile/ports-internal.h (scm_port_buffer_can_take):
  (scm_port_buffer_can_put): Add cur/end output arguments so that when a
  caller asks the buffer room, it can be relative to a fixed point in
  the buffer and not whatever point it's at when we go to fill it.
  (scm_port_buffer_did_take, scm_port_buffer_did_put): Similarly,
  require that the caller knows where they took/put data in the buffer.
  Prevents overflow.
  (scm_port_buffer_take_pointer, scm_port_buffer_put_pointer): Likewise,
  require that the caller has already checked and knows a position in
  the buffer and therefore how much data is available.
  (scm_port_buffer_take, scm_port_buffer_put, scm_port_buffer_putback):
  Adapt.
* libguile/ports.h (scm_fill_input): Add cur/avail output arguments.
* libguile/filesys.c:
* libguile/poll.c:
* libguile/ports.c:
* libguile/r6rs-ports.c:
* libguile/read.c:
* libguile/rw.c: Adapt all callers.  Gnarly work!
This commit is contained in:
Andy Wingo 2017-02-08 15:05:03 +01:00
parent 8a4774dec8
commit 09a69dd712
8 changed files with 251 additions and 176 deletions
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10
libguile/poll.c
View file

@ -108,12 +108,13 @@ scm_primitive_poll (SCM pollfds, SCM nfds, SCM ports, SCM timeout)
else
{
scm_t_port *pt = SCM_PORT (port);
size_t tmp;
if (scm_port_buffer_can_take (pt->read_buf) > 0)
if (scm_port_buffer_can_take (pt->read_buf, &tmp) > 0)
/* Buffered input waiting to be read. */
revents |= POLLIN;
if (SCM_OUTPUT_PORT_P (port)
&& scm_port_buffer_can_put (pt->write_buf) > 1)
&& scm_port_buffer_can_put (pt->write_buf, &tmp) > 1)
/* Buffered output possible. The "> 1" is because
writing the last byte would flush the port. */
revents |= POLLOUT;
@ -146,12 +147,13 @@ scm_primitive_poll (SCM pollfds, SCM nfds, SCM ports, SCM timeout)
else
{
scm_t_port *pt = SCM_PORT (port);
size_t tmp;
if (scm_port_buffer_can_take (pt->read_buf) > 0)
if (scm_port_buffer_can_take (pt->read_buf, &tmp) > 0)
/* Buffered input waiting to be read. */
revents |= POLLIN;
if (SCM_OUTPUT_PORT_P (port)
&& scm_port_buffer_can_put (pt->write_buf) > 1)
&& scm_port_buffer_can_put (pt->write_buf, &tmp) > 1)
/* Buffered output possible. The "> 1" is because
writing the last byte would flush the port. */
revents |= POLLOUT;