src/lib/buffer.c

/* Copyright (c) 2002-2018 Dovecot authors, see the included COPYING file */

/* @UNSAFE: whole file */

#include "lib.h"
#include "buffer.h"

struct real_buffer {
	union {
		struct buffer buf;
		struct {
			/* public: */
			const void *r_buffer;
			size_t used;
			/* private: */
			unsigned char *w_buffer;
			size_t dirty, alloc, writable_size, max_size;

			pool_t pool;

			bool alloced:1;
			bool dynamic:1;
		};
	};
};
typedef int buffer_check_sizes[COMPILE_ERROR_IF_TRUE(sizeof(struct real_buffer) > sizeof(buffer_t)) ?1:1];

static void buffer_alloc(struct real_buffer *buf, size_t size)
{
	i_assert(buf->w_buffer == NULL || buf->alloced);

	if (size == buf->alloc)
		return;

	i_assert(size > buf->alloc);

	if (buf->w_buffer == NULL)
		buf->w_buffer = p_malloc(buf->pool, size);
	else
		buf->w_buffer = p_realloc(buf->pool, buf->w_buffer, buf->alloc, size);
	buf->alloc = size;
	buf->writable_size = size-1; /* -1 for str_c() NUL */

	buf->r_buffer = buf->w_buffer;
	buf->alloced = TRUE;
}

static inline void
buffer_check_limits(struct real_buffer *buf, size_t pos, size_t data_size)
{
	size_t new_size;

	if (unlikely(buf->max_size - pos < data_size))
		i_panic("Buffer write out of range (%zu + %zu)", pos, data_size);

	new_size = pos + data_size;

	if (new_size > buf->used && buf->used < buf->dirty) {
		/* clear used..dirty area */
		size_t max = I_MIN(I_MIN(buf->alloc, buf->dirty), new_size);

		memset(buf->w_buffer + buf->used, 0, max - buf->used);
	}

	/* Use buf->writable_size instead of buf->alloc to always keep +1 byte
	   available in case str_c() is called for this buffer. This is mainly
	   for cases where the buffer is allocated from data stack, and str_c()
	   is called in a separate stack frame. */
	if (new_size > buf->writable_size) {
		if (unlikely(!buf->dynamic)) {
			i_panic("Buffer full (%zu > %zu, pool %s)",
				pos + data_size, buf->alloc,
				buf->pool == NULL ? "<none>" :
				pool_get_name(buf->pool));
		}

		size_t new_alloc_size =
			pool_get_exp_grown_size(buf->pool, buf->alloc,
						new_size + 1);
		if (new_alloc_size > buf->max_size) {
			/* limit to max_size, but do include +1 for
			   str_c() NUL */
			new_alloc_size = buf->max_size + 1;
		}
		buffer_alloc(buf, new_alloc_size);
	}
#if 0
	else if (new_size > buf->used && buf->alloced &&
		 !buf->pool->alloconly_pool && !buf->pool->datastack_pool) {
		void *new_buf;

		/* buffer's size increased: move the buffer's memory elsewhere.
		   this should help catch bugs where old pointers are tried to
		   be used to access the buffer's memory */
		new_buf = p_malloc(buf->pool, buf->alloc);
		memcpy(new_buf, buf->w_buffer, buf->alloc);
		p_free(buf->pool, buf->w_buffer);

		buf->w_buffer = new_buf;
		buf->r_buffer = new_buf;
	}
#endif

	if (new_size > buf->used)
		buf->used = new_size;
	i_assert(buf->used <= buf->alloc);
	i_assert(buf->w_buffer != NULL);
}

static inline void
buffer_check_append_limits(struct real_buffer *buf, size_t data_size)
{
	/* Fast path: See if data to be appended fits into allocated buffer.
	   If it does, we don't even need to memset() the dirty buffer since
	   it's going to be filled with the newly appended data. */
	if (buf->writable_size - buf->used < data_size)
		buffer_check_limits(buf, buf->used, data_size);
	else
		buf->used += data_size;
}

#undef buffer_create_from_data
void buffer_create_from_data(buffer_t *buffer, void *data, size_t size)
{
	struct real_buffer *buf;

	i_assert(sizeof(*buffer) >= sizeof(struct real_buffer));

	buf = container_of(buffer, struct real_buffer, buf);
	i_zero(buf);
	buf->alloc = buf->writable_size = buf->max_size = size;
	buf->r_buffer = buf->w_buffer = data;
	/* clear the whole memory area. unnecessary usually, but if the
	   buffer is used by e.g. str_c() it tries to access uninitialized
	   memory */
	memset(data, 0, size);
}

#undef buffer_create_from_const_data
void buffer_create_from_const_data(buffer_t *buffer,
				   const void *data, size_t size)
{
	struct real_buffer *buf;

	i_assert(sizeof(*buffer) >= sizeof(struct real_buffer));

	buf = container_of(buffer, struct real_buffer, buf);
	i_zero(buf);

	buf->used = buf->alloc = buf->writable_size = buf->max_size = size;
	buf->r_buffer = data;
	i_assert(buf->w_buffer == NULL);
}

buffer_t *buffer_create_dynamic(pool_t pool, size_t init_size)
{
	return buffer_create_dynamic_max(pool, init_size, SIZE_MAX);
}

buffer_t *buffer_create_dynamic_max(pool_t pool, size_t init_size,
				    size_t max_size)
{
	struct real_buffer *buf;

#ifdef DEBUG
	/* we increment this by 1 later on, so if it's SIZE_MAX
	   it turns into 0 and hides a potential bug.

	   Too scary to use in production for now, though. This
	   can change in future. */
	i_assert(init_size < SIZE_MAX);
#endif

	buf = p_new(pool, struct real_buffer, 1);
	buf->pool = pool;
	buf->dynamic = TRUE;
	buf->max_size = max_size;
	/* buffer_alloc() reserves +1 for str_c() NIL, so add +1 here to
	   init_size so we can actually write that much to the buffer without
	   realloc */
	buffer_alloc(buf, init_size+1);
	return &buf->buf;
}

void buffer_free(buffer_t **_buf)
{
	struct real_buffer *buf = container_of(*_buf, struct real_buffer, buf);

	if (buf == NULL)
		return;

	*_buf = NULL;
	if (buf->alloced)
		p_free(buf->pool, buf->w_buffer);
	if (buf->pool != NULL)
		p_free(buf->pool, buf);
}

void *buffer_free_without_data(buffer_t **_buf)
{
	struct real_buffer *buf = container_of(*_buf, struct real_buffer, buf);
	void *data;

	*_buf = NULL;

	data = buf->w_buffer;
	p_free(buf->pool, buf);
	return data;
}

pool_t buffer_get_pool(const buffer_t *_buf)
{
	const struct real_buffer *buf =
		container_of(_buf, const struct real_buffer, buf);

	return buf->pool;
}

void buffer_write(buffer_t *_buf, size_t pos,
		  const void *data, size_t data_size)
{
	struct real_buffer *buf = container_of(_buf, struct real_buffer, buf);

	buffer_check_limits(buf, pos, data_size);
	if (data_size > 0)
		memcpy(buf->w_buffer + pos, data, data_size);
}

void buffer_append(buffer_t *_buf, const void *data, size_t data_size)
{
	struct real_buffer *buf = container_of(_buf, struct real_buffer, buf);

	if (data_size > 0) {
		size_t pos = buf->used;
		buffer_check_append_limits(buf, data_size);
		memcpy(buf->w_buffer + pos, data, data_size);
	}
}

void buffer_append_c(buffer_t *_buf, unsigned char chr)
{
	struct real_buffer *buf = container_of(_buf, struct real_buffer, buf);
	size_t pos = buf->used;

	buffer_check_append_limits(buf, 1);
	buf->w_buffer[pos] = chr;
}

void buffer_insert(buffer_t *_buf, size_t pos,
		   const void *data, size_t data_size)
{
	struct real_buffer *buf = container_of(_buf, struct real_buffer, buf);

	if (pos >= buf->used)
		buffer_write(_buf, pos, data, data_size);
	else {
		buffer_copy(_buf, pos + data_size, _buf, pos, SIZE_MAX);
		memcpy(buf->w_buffer + pos, data, data_size);
	}
}

void buffer_delete(buffer_t *_buf, size_t pos, size_t size)
{
	struct real_buffer *buf = container_of(_buf, struct real_buffer, buf);
	size_t end_size;

	if (pos >= buf->used)
		return;
	end_size = buf->used - pos;

	if (size < end_size) {
		/* delete from between */
		end_size -= size;
		memmove(buf->w_buffer + pos,
			buf->w_buffer + pos + size, end_size);
	} else {
		/* delete the rest of the buffer */
		end_size = 0;
	}

	buffer_set_used_size(_buf, pos + end_size);
}

void buffer_replace(buffer_t *_buf, size_t pos, size_t size,
		    const void *data, size_t data_size)
{
	struct real_buffer *buf = container_of(_buf, struct real_buffer, buf);
	size_t end_size;

	if (pos >= buf->used) {
		buffer_write(_buf, pos, data, data_size);
		return;
	}
	end_size = buf->used - pos;

	if (size < end_size) {
		end_size -= size;
		if (data_size == 0) {
			/* delete from between */
			memmove(buf->w_buffer + pos,
				buf->w_buffer + pos + size, end_size);
		} else {
			/* insert */
			buffer_copy(_buf, pos + data_size, _buf, pos + size,
				    SIZE_MAX);
			memcpy(buf->w_buffer + pos, data, data_size);
		}
	} else {
		/* overwrite the end */
		end_size = 0;
		buffer_write(_buf, pos, data, data_size);
	}

	buffer_set_used_size(_buf, pos + data_size + end_size);
}


void buffer_write_zero(buffer_t *_buf, size_t pos, size_t data_size)
{
	struct real_buffer *buf = container_of(_buf, struct real_buffer, buf);

	buffer_check_limits(buf, pos, data_size);
	memset(buf->w_buffer + pos, 0, data_size);
}

void buffer_append_zero(buffer_t *_buf, size_t data_size)
{
	struct real_buffer *buf = container_of(_buf, struct real_buffer, buf);

	/* NOTE: When appending it's enough to check that the limits are
	   valid, because the data is already guaranteed to be zero-filled. */
	buffer_check_limits(buf, buf->used, data_size);
}

void buffer_insert_zero(buffer_t *_buf, size_t pos, size_t data_size)
{
	struct real_buffer *buf = container_of(_buf, struct real_buffer, buf);

	if (pos >= buf->used)
		buffer_write_zero(_buf, pos, data_size);
	else {
		buffer_copy(_buf, pos + data_size, _buf, pos, SIZE_MAX);
		memset(buf->w_buffer + pos, 0, data_size);
	}
}

void buffer_copy(buffer_t *_dest, size_t dest_pos,
		 const buffer_t *_src, size_t src_pos, size_t copy_size)
{
	struct real_buffer *dest = container_of(_dest, struct real_buffer, buf);
	const struct real_buffer *src =
		container_of(_src, const struct real_buffer, buf);
	size_t max_size;

	i_assert(src_pos <= src->used);

	max_size = src->used - src_pos;
	if (copy_size > max_size)
		copy_size = max_size;

	buffer_check_limits(dest, dest_pos, copy_size);
	i_assert(src->r_buffer != NULL);

	if (src == dest) {
		memmove(dest->w_buffer + dest_pos,
			CONST_PTR_OFFSET(src->r_buffer, src_pos), copy_size);
	} else {
		memcpy(dest->w_buffer + dest_pos,
		       CONST_PTR_OFFSET(src->r_buffer, src_pos), copy_size);
	}
}

void buffer_append_buf(buffer_t *dest, const buffer_t *src,
		       size_t src_pos, size_t copy_size)
{
	buffer_copy(dest, dest->used, src, src_pos, copy_size);
}

void *buffer_get_space_unsafe(buffer_t *_buf, size_t pos, size_t size)
{
	struct real_buffer *buf = container_of(_buf, struct real_buffer, buf);

	buffer_check_limits(buf, pos, size);
	return buf->w_buffer + pos;
}

void *buffer_append_space_unsafe(buffer_t *buf, size_t size)
{
	/* NOTE: can't use buffer_check_append_limits() here because it doesn't
	   guarantee that the buffer is zero-filled. */
	return buffer_get_space_unsafe(buf, buf->used, size);
}

void *buffer_get_modifiable_data(const buffer_t *_buf, size_t *used_size_r)
{
	const struct real_buffer *buf =
		container_of(_buf, const struct real_buffer, buf);

	if (used_size_r != NULL)
		*used_size_r = buf->used;
	i_assert(buf->used == 0 || buf->w_buffer != NULL);
	return buf->w_buffer;
}

void buffer_set_used_size(buffer_t *_buf, size_t used_size)
{
	struct real_buffer *buf = container_of(_buf, struct real_buffer, buf);

	i_assert(used_size <= buf->alloc);

	if (buf->used > buf->dirty)
		buf->dirty = buf->used;

	buf->used = used_size;
}

size_t buffer_get_size(const buffer_t *_buf)
{
	const struct real_buffer *buf =
		container_of(_buf, const struct real_buffer, buf);

	return buf->alloc;
}

size_t buffer_get_writable_size(const buffer_t *_buf)
{
	const struct real_buffer *buf =
		container_of(_buf, const struct real_buffer, buf);

	/* Use buf->writable_size instead of buf->alloc to reserve +1 for
	   str_c() NUL in buffer_check_limits(). Otherwise the caller might
	   increase the buffer's alloc size unnecessarily when it just wants
	   to access the entire buffer. */
	return buf->writable_size;
}

size_t buffer_get_avail_size(const buffer_t *_buf)
{
	const struct real_buffer *buf =
		container_of(_buf, const struct real_buffer, buf);

	i_assert(buf->alloc >= buf->used);
	return ((buf->dynamic ? SIZE_MAX : buf->alloc) - buf->used);
}

bool buffer_cmp(const buffer_t *buf1, const buffer_t *buf2)
{
	if (buf1->used != buf2->used)
		return FALSE;
	if (buf1->used == 0)
		return TRUE;

	return memcmp(buf1->data, buf2->data, buf1->used) == 0;
}

void buffer_verify_pool(buffer_t *_buf)
{
	const struct real_buffer *buf =
		container_of(_buf, struct real_buffer, buf);
	void *ret;

	if (buf->pool != NULL && buf->pool->datastack_pool && buf->alloc > 0) {
		/* this doesn't really do anything except verify the
		   stack frame */
		ret = p_realloc(buf->pool, buf->w_buffer,
				buf->alloc, buf->alloc);
		i_assert(ret == buf->w_buffer);
	}
}

void ATTR_NO_SANITIZE_IMPLICIT_CONVERSION
	ATTR_NO_SANITIZE_INTEGER
buffer_truncate_rshift_bits(buffer_t *buf, size_t bits)
{
	/* no-op if it's shorten than bits in any case.. */
	if (buf->used * 8 < bits) return;

	if (bits > 0) {
		/* truncate it to closest byte boundary */
		size_t bytes = ((bits + 7) & -8U)/8;
		/* remaining bits */
		bits = bits % 8;
		buffer_set_used_size(buf, I_MIN(bytes, buf->used));
		unsigned char *ptr = buffer_get_modifiable_data(buf, &bytes);
		/* right shift over byte array */
		if (bits > 0) {
			for(size_t i=bytes-1;i>0;i--)
				ptr[i] = (ptr[i]>>(8-bits)) +
					 ((ptr[i-1]&(0xff>>(bits)))<<bits);
			ptr[0] = ptr[0]>>(8-bits);
		}
	} else {
		buffer_set_used_size(buf, 0);
	}
}