Taint: hybrid checking mode

[exim.git] / src / src / store.c

diff --git a/src/src/store.c b/src/src/store.c
index fbfd20d1de64d34fb276e183aad8483b91cc872b..aceb0e5d66789d50f128698e3b0178407de75343 100644 (file)
--- a/src/src/store.c
+++ b/src/src/store.c
@@ -49,18 +49,24 @@ The following different types of store are recognized:
   to not copy untrusted data into untainted memory, as downstream taint-checks
   would be avoided.
 
-  Intermediate layers (eg. the string functions) can test for taint, and use this
-  for ensuringn 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.
-
   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).
 */
 
 
@@ -180,8 +186,14 @@ static void   internal_tainted_free(storeblock *, const char *, int linenumber);
 
 /******************************************************************************/
 
-/* Slower version check, for use when platform intermixes malloc and mmap area
-addresses. */
+/* 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)
@@ -189,23 +201,20 @@ 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;
+    uschar * bc = US b + ALIGNED_SIZEOF_STOREBLOCK;
+    if (US p >= bc && US 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;
+    uschar * bc = US b + ALIGNED_SIZEOF_STOREBLOCK;
+    if (US p >= bc && US p <= bc + b->length) return TRUE;
     }
 return FALSE;
-
-hit:
-return pool >= POOL_TAINT_BASE;
 }
 
 
@@ -216,6 +225,13 @@ log_write(0, LOG_MAIN|LOG_PANIC_DIE, "Taint mismatch, %s: %s %d\n",
        msg, func, line);
 }
 
+static void
+use_slow_taint_check(void)
+{
+DEBUG(D_any) debug_printf("switching to slow-mode taint checking\n");
+f.taint_check_slow = TRUE;
+}
+
 
 /*************************************************
 *       Get a block from the current pool        *
@@ -839,6 +855,14 @@ if (!(yield = malloc((size_t)size)))
   log_write(0, LOG_MAIN|LOG_PANIC_DIE, "failed to malloc %d bytes of memory: "
     "called from line %d in %s", size, linenumber, func);
 
+/* If malloc ever returns apparently tainted memory, which glibc
+malloc will as it uses mmap for larger requests, we must switch to
+the slower checking for tainting (checking an address against all
+the tainted pool block spans, rather than just the mmap span) */
+
+if (!f.taint_check_slow && is_tainted(yield))
+  use_slow_taint_check();
+
 return store_alloc_tail(yield, size, func, linenumber, US"Malloc");
 }