Commit 8f857c23 authored by Nick Mathewson's avatar Nick Mathewson 🦀
Browse files

Add a one-word sentinel value of 0x0 at the end of each buf_t chunk 

This helps protect against bugs where any part of a buf_t's memory
is passed to a function that expects a NUL-terminated input.
parent 0fb3058e

src/or/buffers.c

+28 −3
Original line number Diff line number Diff line
@@ -75,12 +75,33 @@ typedef struct chunk_t { 


#define CHUNK_HEADER_LEN STRUCT_OFFSET(chunk_t, mem[0])



/* We leave this many NUL bytes at the end of the buffer. */

#define SENTINEL_LEN 4



/* Header size plus NUL bytes at the end */

#define CHUNK_OVERHEAD (CHUNK_HEADER_LEN + SENTINEL_LEN)



/** Return the number of bytes needed to allocate a chunk to hold

 * <b>memlen</b> bytes. */

#define CHUNK_ALLOC_SIZE(memlen) (CHUNK_HEADER_LEN + (memlen))

#define CHUNK_ALLOC_SIZE(memlen) (CHUNK_OVERHEAD + (memlen))

/** Return the number of usable bytes in a chunk allocated with

 * malloc(<b>memlen</b>). */

#define CHUNK_SIZE_WITH_ALLOC(memlen) ((memlen) - CHUNK_HEADER_LEN)

#define CHUNK_SIZE_WITH_ALLOC(memlen) ((memlen) - CHUNK_OVERHEAD)



#define DEBUG_SENTINEL



#ifdef DEBUG_SENTINEL

#define DBG_S(s) s

#else

#define DBG_S(s) (void)0

#endif



#define CHUNK_SET_SENTINEL(chunk, alloclen) do {                        \

    uint8_t *a = (uint8_t*) &(chunk)->mem[(chunk)->memlen];             \

    DBG_S(uint8_t *b = &((uint8_t*)(chunk))[(alloclen)-SENTINEL_LEN]);  \

    DBG_S(tor_assert(a == b));                                          \

    memset(a,0,SENTINEL_LEN);                                           \

  } while (0)



/** Return the next character in <b>chunk</b> onto which data can be appended.

 * If the chunk is full, this might be off the end of chunk->mem. */
@@ -204,6 +225,7 @@ chunk_new_with_alloc_size(size_t alloc) 
  ch->datalen = 0;

  ch->memlen = CHUNK_SIZE_WITH_ALLOC(alloc);

  ch->data = &ch->mem[0];

  CHUNK_SET_SENTINEL(ch, alloc);

  return ch;

}

#else
@@ -221,6 +243,7 @@ chunk_new_with_alloc_size(size_t alloc) 
  ch->datalen = 0;

  ch->memlen = CHUNK_SIZE_WITH_ALLOC(alloc);

  ch->data = &ch->mem[0];

  CHUNK_SET_SENTINEL(ch, alloc);

  return ch;

}

#endif
@@ -231,11 +254,13 @@ static INLINE chunk_t * 
chunk_grow(chunk_t *chunk, size_t sz)

{

  off_t offset;

  const size_t new_alloc = CHUNK_ALLOC_SIZE(sz);

  tor_assert(sz > chunk->memlen);

  offset = chunk->data - chunk->mem;

  chunk = tor_realloc(chunk, CHUNK_ALLOC_SIZE(sz));

  chunk = tor_realloc(chunk, new_alloc);

  chunk->memlen = sz;

  chunk->data = chunk->mem + offset;

  CHUNK_SET_SENTINEL(chunk, new_alloc);

  return chunk;

}