xemu/slirp/mbuf.c
Peter Maydell 09b94ac0f2 slirp: Correct size check in m_inc()
The data in an mbuf buffer is not necessarily at the start of the
allocated buffer. (For instance m_adj() allows data to be trimmed
from the start by just advancing the pointer and reducing the length.)
This means that the allocated buffer size (m->m_size) and the
amount of space from the m_data pointer to the end of the
buffer (M_ROOM(m)) are not necessarily the same.

Commit 864036e251 tried to change the m_inc() function from
taking the new allocated-buffer-size to taking the new room-size,
but forgot to change the initial "do we already have enough space"
check. This meant that if we were trying to extend a buffer which
had a leading gap between the buffer start and the data, we might
incorrectly decide it didn't need to be extended, and then
overrun the end of the buffer, causing memory corruption and
an eventual crash.

Change the "already big enough?" condition from checking the
argument against m->m_size to checking against M_ROOM().
This only makes a difference for the callsite in m_cat();
the other three callsites all start with a freshly allocated
mbuf from m_get(), which will have m->m_size == M_ROOM(m).

Fixes: 864036e251
Fixes: https://bugs.launchpad.net/qemu/+bug/1785670
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
Message-id: 20180807114501.12370-1-peter.maydell@linaro.org
Tested-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
2018-08-07 14:13:22 +01:00

239 lines
5.1 KiB
C

/*
* Copyright (c) 1995 Danny Gasparovski
*
* Please read the file COPYRIGHT for the
* terms and conditions of the copyright.
*/
/*
* mbuf's in SLiRP are much simpler than the real mbufs in
* FreeBSD. They are fixed size, determined by the MTU,
* so that one whole packet can fit. Mbuf's cannot be
* chained together. If there's more data than the mbuf
* could hold, an external g_malloced buffer is pointed to
* by m_ext (and the data pointers) and M_EXT is set in
* the flags
*/
#include "qemu/osdep.h"
#include "slirp.h"
#define MBUF_THRESH 30
/*
* Find a nice value for msize
*/
#define SLIRP_MSIZE\
(offsetof(struct mbuf, m_dat) + IF_MAXLINKHDR + TCPIPHDR_DELTA + IF_MTU)
void
m_init(Slirp *slirp)
{
slirp->m_freelist.qh_link = slirp->m_freelist.qh_rlink = &slirp->m_freelist;
slirp->m_usedlist.qh_link = slirp->m_usedlist.qh_rlink = &slirp->m_usedlist;
}
void m_cleanup(Slirp *slirp)
{
struct mbuf *m, *next;
m = (struct mbuf *) slirp->m_usedlist.qh_link;
while ((struct quehead *) m != &slirp->m_usedlist) {
next = m->m_next;
if (m->m_flags & M_EXT) {
g_free(m->m_ext);
}
g_free(m);
m = next;
}
m = (struct mbuf *) slirp->m_freelist.qh_link;
while ((struct quehead *) m != &slirp->m_freelist) {
next = m->m_next;
g_free(m);
m = next;
}
}
/*
* Get an mbuf from the free list, if there are none
* allocate one
*
* Because fragmentation can occur if we alloc new mbufs and
* free old mbufs, we mark all mbufs above mbuf_thresh as M_DOFREE,
* which tells m_free to actually g_free() it
*/
struct mbuf *
m_get(Slirp *slirp)
{
register struct mbuf *m;
int flags = 0;
DEBUG_CALL("m_get");
if (slirp->m_freelist.qh_link == &slirp->m_freelist) {
m = g_malloc(SLIRP_MSIZE);
slirp->mbuf_alloced++;
if (slirp->mbuf_alloced > MBUF_THRESH)
flags = M_DOFREE;
m->slirp = slirp;
} else {
m = (struct mbuf *) slirp->m_freelist.qh_link;
remque(m);
}
/* Insert it in the used list */
insque(m,&slirp->m_usedlist);
m->m_flags = (flags | M_USEDLIST);
/* Initialise it */
m->m_size = SLIRP_MSIZE - offsetof(struct mbuf, m_dat);
m->m_data = m->m_dat;
m->m_len = 0;
m->m_nextpkt = NULL;
m->m_prevpkt = NULL;
m->resolution_requested = false;
m->expiration_date = (uint64_t)-1;
DEBUG_ARG("m = %p", m);
return m;
}
void
m_free(struct mbuf *m)
{
DEBUG_CALL("m_free");
DEBUG_ARG("m = %p", m);
if(m) {
/* Remove from m_usedlist */
if (m->m_flags & M_USEDLIST)
remque(m);
/* If it's M_EXT, free() it */
if (m->m_flags & M_EXT) {
g_free(m->m_ext);
}
/*
* Either free() it or put it on the free list
*/
if (m->m_flags & M_DOFREE) {
m->slirp->mbuf_alloced--;
g_free(m);
} else if ((m->m_flags & M_FREELIST) == 0) {
insque(m,&m->slirp->m_freelist);
m->m_flags = M_FREELIST; /* Clobber other flags */
}
} /* if(m) */
}
/*
* Copy data from one mbuf to the end of
* the other.. if result is too big for one mbuf, allocate
* an M_EXT data segment
*/
void
m_cat(struct mbuf *m, struct mbuf *n)
{
/*
* If there's no room, realloc
*/
if (M_FREEROOM(m) < n->m_len)
m_inc(m, m->m_len + n->m_len);
memcpy(m->m_data+m->m_len, n->m_data, n->m_len);
m->m_len += n->m_len;
m_free(n);
}
/* make m 'size' bytes large from m_data */
void
m_inc(struct mbuf *m, int size)
{
int datasize;
/* some compilers throw up on gotos. This one we can fake. */
if (M_ROOM(m) > size) {
return;
}
if (m->m_flags & M_EXT) {
datasize = m->m_data - m->m_ext;
m->m_ext = g_realloc(m->m_ext, size + datasize);
} else {
datasize = m->m_data - m->m_dat;
m->m_ext = g_malloc(size + datasize);
memcpy(m->m_ext, m->m_dat, m->m_size);
m->m_flags |= M_EXT;
}
m->m_data = m->m_ext + datasize;
m->m_size = size + datasize;
}
void
m_adj(struct mbuf *m, int len)
{
if (m == NULL)
return;
if (len >= 0) {
/* Trim from head */
m->m_data += len;
m->m_len -= len;
} else {
/* Trim from tail */
len = -len;
m->m_len -= len;
}
}
/*
* Copy len bytes from m, starting off bytes into n
*/
int
m_copy(struct mbuf *n, struct mbuf *m, int off, int len)
{
if (len > M_FREEROOM(n))
return -1;
memcpy((n->m_data + n->m_len), (m->m_data + off), len);
n->m_len += len;
return 0;
}
/*
* Given a pointer into an mbuf, return the mbuf
* XXX This is a kludge, I should eliminate the need for it
* Fortunately, it's not used often
*/
struct mbuf *
dtom(Slirp *slirp, void *dat)
{
struct mbuf *m;
DEBUG_CALL("dtom");
DEBUG_ARG("dat = %p", dat);
/* bug corrected for M_EXT buffers */
for (m = (struct mbuf *) slirp->m_usedlist.qh_link;
(struct quehead *) m != &slirp->m_usedlist;
m = m->m_next) {
if (m->m_flags & M_EXT) {
if( (char *)dat>=m->m_ext && (char *)dat<(m->m_ext + m->m_size) )
return m;
} else {
if( (char *)dat >= m->m_dat && (char *)dat<(m->m_dat + m->m_size) )
return m;
}
}
DEBUG_ERROR((dfd, "dtom failed"));
return (struct mbuf *)0;
}