X-Git-Url: https://git.exim.org/exim.git/blobdiff_plain/81a559c80ccd6a0354b5485720c0205a69289fb5..1c519e07b908a314ce7bdfceb6baa9e18e302dfc:/src/src/store.c

diff --git a/src/src/store.c b/src/src/store.c
index 9b1a297e6..61f9464af 100644
--- a/src/src/store.c
+++ b/src/src/store.c
@@ -41,8 +41,32 @@ The following different types of store are recognized:
   and tainted.  The latter is used for values derived from untrusted input, and
   the string-expansion mechanism refuses to operate on such values (obviously,
   it can expand an untainted value to return a tainted result).  The classes
-  are implemented by duplicating the three pool types. Pool resets are requested
+  are implemented by duplicating the three pool types.  Pool resets are requested
   against the nontainted sibling and apply to both siblings.
+
+  Only memory blocks requested for tainted use are regarded as tainted; anything
+  else (including stack auto variables) is untainted.  Care is needed when coding
+  to not copy untrusted data into untainted memory, as downstream taint-checks
+  would be avoided.
+
+  Internally we currently use malloc for nontainted pools, and mmap for tainted
+  pools.  The disparity is for speed of testing the taintedness of pointers;
+  because Linux appears to use distinct non-overlapping address allocations for
+  mmap vs. everything else, which means only two pointer-compares suffice for the
+  test.  Other OS' cannot use that optimisation, and a more lengthy test against
+  the limits of tainted-pool allcations has to be done.
+
+  Intermediate layers (eg. the string functions) can test for taint, and use this
+  for ensurinng that results have proper state.  For example the
+  string_vformat_trc() routing supporting the string_sprintf() interface will
+  recopy a string being built into a tainted allocation if it meets a %s for a
+  tainted argument.  Any intermediate-layer function that (can) return a new
+  allocation should behave this way; returning a tainted result if any tainted
+  content is used.  Intermediate-layer functions (eg. Ustrncpy) that modify
+  existing allocations fail if tainted data is written into an untainted area.
+  Users of functions that modify existing allocations should check if a tainted
+  source and an untainted destination is used, and fail instead (sprintf() being
+  the classic case).
 */
 
 
@@ -157,12 +181,20 @@ static const uschar * poolclass[NPOOLS] = {
 
 static void * store_mmap(int, const char *, int);
 static void * internal_store_malloc(int, const char *, int);
-static void   internal_store_free(void *, const char *, int linenumber);
+static void   internal_untainted_free(void *, const char *, int linenumber);
+static void   internal_tainted_free(storeblock *, const char *, int linenumber);
 
 /******************************************************************************/
 
-/* Slower version check, for use when platform intermixes malloc and mmap area
-addresses. */
+#ifndef TAINT_CHECK_FAST
+/* Test if a pointer refers to tainted memory.
+
+Slower version check, for use when platform intermixes malloc and mmap area
+addresses. Test against the current-block of all tainted pools first, then all
+blocks of all tainted pools.
+
+Return: TRUE iff tainted
+*/
 
 BOOL
 is_tainted_fn(const void * p)
@@ -170,24 +202,22 @@ is_tainted_fn(const void * p)
 storeblock * b;
 int pool;
 
-for (pool = 0; pool < nelem(chainbase); pool++)
+for (pool = POOL_TAINT_BASE; pool < nelem(chainbase); pool++)
   if ((b = current_block[pool]))
     {
     char * bc = CS b + ALIGNED_SIZEOF_STOREBLOCK;
-    if (CS p >= bc && CS p <= bc + b->length) goto hit;
+    if (CS p >= bc && CS p <= bc + b->length) return TRUE;
     }
 
-for (pool = 0; pool < nelem(chainbase); pool++)
+for (pool = POOL_TAINT_BASE; pool < nelem(chainbase); pool++)
   for (b = chainbase[pool]; b; b = b->next)
     {
     char * bc = CS b + ALIGNED_SIZEOF_STOREBLOCK;
-    if (CS p >= bc && CS p <= bc + b->length) goto hit;
+    if (CS p >= bc && CS p <= bc + b->length) return TRUE;
     }
 return FALSE;
-
-hit:
-return pool >= POOL_TAINT_BASE;
 }
+#endif
 
 
 void
@@ -208,7 +238,8 @@ block, getting a new one if necessary. The address is saved in
 store_last_was_get.
 
 Arguments:
-  size        amount wanted
+  size        amount wanted, bytes
+  tainted     class: set to true for untrusted data (eg. from smtp input)
   func        function from which called
   linenumber  line number in source file
 
@@ -248,15 +279,9 @@ if (size > yield_length[pool])
     /* Give up on this block, because it's too small */
     nblocks[pool]--;
     if (pool < POOL_TAINT_BASE)
-      internal_store_free(newblock, func, linenumber);
+      internal_untainted_free(newblock, func, linenumber);
     else
-      {
-#ifndef COMPILE_UTILITY
-      DEBUG(D_memory)
-	debug_printf("---Unmap %6p %-20s %4d\n", newblock, func, linenumber);
-#endif
-      munmap(newblock, newblock->length + ALIGNED_SIZEOF_STOREBLOCK);
-      }
+      internal_tainted_free(newblock, func, linenumber);
     newblock = NULL;
     }
 
@@ -515,15 +540,9 @@ while ((b = bb))
   pool_malloc -= siz;
   nblocks[pool]--;
   if (pool < POOL_TAINT_BASE)
-    internal_store_free(b, func, linenumber);
+    internal_untainted_free(b, func, linenumber);
   else
-    {
-#ifndef COMPILE_UTILITY
-    DEBUG(D_memory)
-      debug_printf("---Unmap %6p %-20s %4d\n", b, func, linenumber);
-#endif
-    munmap(b, b->length + ALIGNED_SIZEOF_STOREBLOCK);
-    }
+    internal_tainted_free(b, func, linenumber);
   }
 
 /* Cut out the debugging stuff for utilities, but stop picky compilers from
@@ -799,7 +818,7 @@ if (!(yield = mmap(NULL, (size_t)size,
     "called from line %d of %s", size, line, func);
 
 if (yield < tainted_base) tainted_base = yield;
-if ((top = yield + size) > tainted_top) tainted_top = top;
+if ((top = US yield + size) > tainted_top) tainted_top = top;
 
 return store_alloc_tail(yield, size, func, line, US"Mmap");
 }
@@ -858,7 +877,7 @@ Returns:      nothing
 */
 
 static void
-internal_store_free(void *block, const char *func, int linenumber)
+internal_untainted_free(void * block, const char * func, int linenumber)
 {
 #ifdef COMPILE_UTILITY
 func = func;
@@ -871,10 +890,24 @@ free(block);
 }
 
 void
-store_free_3(void *block, const char *func, int linenumber)
+store_free_3(void * block, const char * func, int linenumber)
 {
 n_nonpool_blocks--;
-internal_store_free(block, func, linenumber);
+internal_untainted_free(block, func, linenumber);
+}
+
+/******************************************************************************/
+static void
+internal_tainted_free(storeblock * block, const char * func, int linenumber)
+{
+#ifdef COMPILE_UTILITY
+func = func;
+linenumber = linenumber;
+#else
+DEBUG(D_memory)
+  debug_printf("---Unmap %6p %-20s %4d\n", block, func, linenumber);
+#endif
+munmap((void *)block, block->length + ALIGNED_SIZEOF_STOREBLOCK);
 }
 
 /******************************************************************************/