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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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5
libguile/filesys.c
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@ -647,20 +647,21 @@ set_element (fd_set *set, SCM *ports_ready, SCM element, int pos)
else
{
int use_buf = 0;
size_t cur;
element = SCM_COERCE_OUTPORT (element);
SCM_ASSERT (SCM_OPFPORTP (element), element, pos, "select");
if (pos == SCM_ARG1)
{
/* Check whether port has input buffered. */
if (scm_port_buffer_can_take (SCM_PORT (element)->read_buf) > 0)
if (scm_port_buffer_can_take (SCM_PORT (element)->read_buf, &cur) > 0)
use_buf = 1;
}
else if (pos == SCM_ARG2)
{
/* Check whether port's output buffer has room. > 1 since
writing the last byte in the buffer causes flush. */
if (scm_port_buffer_can_put (SCM_PORT (element)->write_buf) > 1)
if (scm_port_buffer_can_put (SCM_PORT (element)->write_buf, &cur) > 1)
use_buf = 1;
}
fd = use_buf ? -1 : SCM_FPORT_FDES (element);