DEBUG: data-stack buffer overflow checking code was causing false positives.

--HG--
branch : HEAD

diff --git a/src/lib/data-stack.c b/src/lib/data-stack.c
index b3e00dd16ed0f0c62bd3eae962e9fffe04fce7a4..fe5977ee7a121776e8595c3882f12d13116d67e2 100644 (file)
--- a/src/lib/data-stack.c
+++ b/src/lib/data-stack.c
@@ -72,11 +72,11 @@ static union {
        unsigned char data[128];
 } outofmem_area;
 
-static void data_stack_last_buffer_reset(void)
+static void data_stack_last_buffer_reset(bool preserve_data ATTR_UNUSED)
 {
        if (last_buffer_block != NULL) {
 #ifdef DEBUG
-               const unsigned char *p;
+               unsigned char *p;
                unsigned int i;
 
                p = STACK_BLOCK_DATA(current_block) +
@@ -95,6 +95,12 @@ static void data_stack_last_buffer_reset(void)
                        if (p[i] != CLEAR_CHR)
                                i_panic("t_buffer_get(): buffer overflow");
                }
+
+               if (!preserve_data) {
+                       p = STACK_BLOCK_DATA(current_block) +
+                               (current_block->size - current_block->left);
+                       memset(p, CLEAR_CHR, SENTRY_COUNT);
+               }
 #endif
        }
 }
@@ -134,7 +140,7 @@ unsigned int t_push(void)
                frame_block->prev = current_frame_block;
                current_frame_block = frame_block;
        }
-       data_stack_last_buffer_reset();
+       data_stack_last_buffer_reset(FALSE);
 
        /* mark our current position */
        current_frame_block->block[frame_pos] = current_block;
@@ -197,14 +203,9 @@ static void t_pop_verify(void)
                        }
                }
 
-               /* we could verify here that the rest of the buffer contains
-                  CLEAR_CHRs, but it would slow us down a bit too much. */
-               max_pos = block->size - pos < SENTRY_COUNT ?
-                       block->size - pos : SENTRY_COUNT;
-               for (; pos < max_pos; pos++) {
-                       if (p[pos] != CLEAR_CHR)
-                               i_panic("data stack: buffer overflow");
-               }
+               /* if we had used t_buffer_get(), the rest of the buffer
+                  may not contain CLEAR_CHRs. but we've already checked all
+                  the allocations, so there's no need to check them anyway. */
                block = block->next;
                pos = 0;
        }
@@ -218,10 +219,10 @@ unsigned int t_pop(void)
        if (unlikely(frame_pos < 0))
                i_panic("t_pop() called with empty stack");
 
+       data_stack_last_buffer_reset(FALSE);
 #ifdef DEBUG
        t_pop_verify();
 #endif
-       data_stack_last_buffer_reset();
 
        /* update the current block */
        current_block = current_frame_block->block[frame_pos];
@@ -317,8 +318,6 @@ static void *t_malloc_real(size_t size, bool permanent)
                data_stack_init();
        }
 
-       data_stack_last_buffer_reset();
-
        /* allocate only aligned amount of memory so alignment comes
           always properly */
 #ifndef DEBUG
@@ -326,6 +325,7 @@ static void *t_malloc_real(size_t size, bool permanent)
 #else
        alloc_size = MEM_ALIGN(sizeof(size)) + MEM_ALIGN(size + SENTRY_COUNT);
 #endif
+       data_stack_last_buffer_reset(TRUE);
 
        /* used for t_try_realloc() */
        current_frame_block->last_alloc_size[frame_pos] = alloc_size;