1 files changed, 325 insertions, 0 deletions
diff --git a/buffer.c b/buffer.c
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index 0000000..7181fca
--- /dev/null
+++ b/buffer.c
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+/*
+ * Dropbear - a SSH2 server
+ * 
+ * Copyright (c) 2002,2003 Matt Johnston
+ * All rights reserved.
+ * 
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ * 
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ * 
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE. */
+
+/* Buffer handling routines, designed to avoid overflows/using invalid data */
+
+#include "includes.h"
+#include "dbutil.h"
+#include "buffer.h"
+
+/* Prevent integer overflows when incrementing buffer position/length.
+ * Calling functions should check arguments first, but this provides a
+ * backstop */
+#define BUF_MAX_INCR 1000000000
+#define BUF_MAX_SIZE 1000000000
+
+/* avoid excessively large numbers, > 5000 bit */
+#define BUF_MAX_MPINT (5000 / 8)
+
+/* Create (malloc) a new buffer of size */
+buffer* buf_new(unsigned int size) {
+
+	buffer* buf;
+	
+	if (size > BUF_MAX_SIZE) {
+		dropbear_exit("buf->size too big");
+	}
+
+	buf = (buffer*)m_malloc(sizeof(buffer));
+
+	if (size > 0) {
+		buf->data = (unsigned char*)m_malloc(size);
+	} else {
+		buf->data = NULL;
+	}
+
+	buf->size = size;
+	buf->pos = 0;
+	buf->len = 0;
+
+	return buf;
+
+}
+
+/* free the buffer's data and the buffer itself */
+void buf_free(buffer* buf) {
+
+	m_free(buf->data)
+	m_free(buf);
+}
+
+/* overwrite the contents of the buffer to clear it */
+void buf_burn(buffer* buf) {
+	
+	m_burn(buf->data, buf->size);
+
+}
+
+/* resize a buffer, pos and len will be repositioned if required */
+void buf_resize(buffer *buf, unsigned int newsize) {
+
+	if (newsize > BUF_MAX_SIZE) {
+		dropbear_exit("buf->size too big");
+	}
+
+	buf->data = m_realloc(buf->data, newsize);
+	buf->size = newsize;
+	buf->len = MIN(newsize, buf->len);
+	buf->pos = MIN(newsize, buf->pos);
+
+}
+
+/* Create a copy of buf, allocating required memory etc. */
+/* The new buffer is sized the same as the length of the source buffer. */
+buffer* buf_newcopy(buffer* buf) {
+	
+	buffer* ret;
+
+	ret = buf_new(buf->len);
+	ret->len = buf->len;
+	memcpy(ret->data, buf->data, buf->len);
+	return ret;
+}
+
+/* Set the length of the buffer */
+void buf_setlen(buffer* buf, unsigned int len) {
+	if (len > buf->size) {
+		dropbear_exit("bad buf_setlen");
+	}
+	buf->len = len;
+}
+
+/* Increment the length of the buffer */
+void buf_incrlen(buffer* buf, unsigned int incr) {
+	if (incr > BUF_MAX_INCR || buf->len + incr > buf->size) {
+		dropbear_exit("bad buf_incrlen");
+	}
+	buf->len += incr;
+}
+/* Set the position of the buffer */
+void buf_setpos(buffer* buf, unsigned int pos) {
+
+	if (pos > buf->len) {
+		dropbear_exit("bad buf_setpos");
+	}
+	buf->pos = pos;
+}
+
+/* increment the postion by incr, increasing the buffer length if required */
+void buf_incrwritepos(buffer* buf, unsigned int incr) {
+	if (incr > BUF_MAX_INCR || buf->pos + incr > buf->size) {
+		dropbear_exit("bad buf_incrwritepos");
+	}
+	buf->pos += incr;
+	if (buf->pos > buf->len) {
+		buf->len = buf->pos;
+	}
+}
+
+/* increment the position by incr, negative values are allowed, to
+ * decrement the pos*/
+void buf_incrpos(buffer* buf,  int incr) {
+	if (incr > BUF_MAX_INCR ||
+			(unsigned int)((int)buf->pos + incr) > buf->len 
+			|| ((int)buf->pos + incr) < 0) {
+		dropbear_exit("bad buf_incrpos");
+	}
+	buf->pos += incr;
+}
+
+/* Get a byte from the buffer and increment the pos */
+unsigned char buf_getbyte(buffer* buf) {
+
+	if (buf->pos >= buf->len) {
+		dropbear_exit("bad buf_getbyte");
+	}
+	return buf->data[buf->pos++];
+}
+
+/* put a byte, incrementing the length if required */
+void buf_putbyte(buffer* buf, unsigned char val) {
+
+	if (buf->pos >= buf->len) {
+		buf_incrlen(buf, 1);
+	}
+	buf->data[buf->pos] = val;
+	buf->pos++;
+}
+
+/* returns an in-place pointer to the buffer, checking that
+ * the next len bytes from that position can be used */
+unsigned char* buf_getptr(buffer* buf, unsigned int len) {
+
+	if (buf->pos + len > buf->len) {
+		dropbear_exit("bad buf_getptr");
+	}
+	return &buf->data[buf->pos];
+}
+
+/* like buf_getptr, but checks against total size, not used length.
+ * This allows writing past the used length, but not past the size */
+unsigned char* buf_getwriteptr(buffer* buf, unsigned int len) {
+
+	if (buf->pos + len > buf->size) {
+		dropbear_exit("bad buf_getwriteptr");
+	}
+	return &buf->data[buf->pos];
+}
+
+/* Return a null-terminated string, it is malloced, so must be free()ed
+ * Note that the string isn't checked for null bytes, hence the retlen
+ * may be longer than what is returned by strlen */
+unsigned char* buf_getstring(buffer* buf, unsigned int *retlen) {
+
+	unsigned int len;
+	unsigned char* ret;
+	len = buf_getint(buf);
+	if (len > MAX_STRING_LEN) {
+		dropbear_exit("string too long");
+	}
+
+	if (retlen != NULL) {
+		*retlen = len;
+	}
+	ret = m_malloc(len+1);
+	memcpy(ret, buf_getptr(buf, len), len);
+	buf_incrpos(buf, len);
+	ret[len] = '\0';
+
+	return ret;
+}
+
+/* Just increment the buffer position the same as if we'd used buf_getstring,
+ * but don't bother copying/malloc()ing for it */
+void buf_eatstring(buffer *buf) {
+
+	buf_incrpos( buf, buf_getint(buf) );
+}
+
+/* Get an uint32 from the buffer and increment the pos */
+unsigned int buf_getint(buffer* buf) {
+	unsigned int ret;
+
+	LOAD32H(ret, buf_getptr(buf, 4));
+	buf_incrpos(buf, 4);
+	return ret;
+}
+
+/* put a 32bit uint into the buffer, incr bufferlen & pos if required */
+void buf_putint(buffer* buf, int unsigned val) {
+
+	STORE32H(val, buf_getwriteptr(buf, 4));
+	buf_incrwritepos(buf, 4);
+
+}
+
+/* put a SSH style string into the buffer, increasing buffer len if required */
+void buf_putstring(buffer* buf, const unsigned char* str, unsigned int len) {
+	
+	buf_putint(buf, len);
+	buf_putbytes(buf, str, len);
+
+}
+
+/* put the set of len bytes into the buffer, incrementing the pos, increasing
+ * len if required */
+void buf_putbytes(buffer *buf, const unsigned char *bytes, unsigned int len) {
+	memcpy(buf_getwriteptr(buf, len), bytes, len);
+	buf_incrwritepos(buf, len);
+}
+	
+
+/* for our purposes we only need positive (or 0) numbers, so will
+ * fail if we get negative numbers */
+void buf_putmpint(buffer* buf, mp_int * mp) {
+
+	unsigned int len, pad = 0;
+	TRACE(("enter buf_putmpint"));
+
+	assert(mp != NULL);
+
+	if (SIGN(mp) == MP_NEG) {
+		dropbear_exit("negative bignum");
+	}
+
+	/* zero check */
+	if (USED(mp) == 1 && DIGIT(mp, 0) == 0) {
+		len = 0;
+	} else {
+		/* SSH spec requires padding for mpints with the MSB set, this code
+		 * implements it */
+		len = mp_count_bits(mp);
+		/* if the top bit of MSB is set, we need to pad */
+		pad = (len%8 == 0) ? 1 : 0;
+		len = len / 8 + 1; /* don't worry about rounding, we need it for
+							  padding anyway when len%8 == 0 */
+
+	}
+
+	/* store the length */
+	buf_putint(buf, len);
+	
+	/* store the actual value */
+	if (len > 0) {
+		if (pad) {
+			buf_putbyte(buf, 0x00);
+		}
+		if (mp_to_unsigned_bin(mp, buf_getwriteptr(buf, len-pad)) != MP_OKAY) {
+			dropbear_exit("mpint error");
+		}
+		buf_incrwritepos(buf, len-pad);
+	}
+
+	TRACE(("leave buf_putmpint"));
+}
+
+/* Retrieve an mp_int from the buffer.
+ * Will fail for -ve since they shouldn't be required here.
+ * Returns DROPBEAR_SUCCESS or DROPBEAR_FAILURE */
+int buf_getmpint(buffer* buf, mp_int* mp) {
+
+	unsigned int len;
+	len = buf_getint(buf);
+	
+	if (len == 0) {
+		mp_zero(mp);
+		return DROPBEAR_SUCCESS;
+	}
+
+	if (len > BUF_MAX_MPINT) {
+		return DROPBEAR_FAILURE;
+	}
+
+	/* check for negative */
+	if (*buf_getptr(buf, 1) & (1 << (CHAR_BIT-1))) {
+		return DROPBEAR_FAILURE;
+	}
+
+	if (mp_read_unsigned_bin(mp, buf_getptr(buf, len), len) != MP_OKAY) {
+		return DROPBEAR_FAILURE;
+	}
+
+	buf_incrpos(buf, len);
+	return DROPBEAR_SUCCESS;
+}