Taint: hybrid checking mode

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

diff --git a/src/src/store.c b/src/src/store.c
index b65649f4aad1db3c55d976b5f55c09e295554b9d..aceb0e5d66789d50f128698e3b0178407de75343 100644 (file)
--- a/src/src/store.c
+++ b/src/src/store.c
@@ -62,9 +62,11 @@ The following different types of store are recognized:
   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.  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).
+  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).
 */
 
 
@@ -184,7 +186,6 @@ static void   internal_tainted_free(storeblock *, const char *, int linenumber);
 
 /******************************************************************************/
 
-#ifndef TAINT_CHECK_FAST
 /* Test if a pointer refers to tainted memory.
 
 Slower version check, for use when platform intermixes malloc and mmap area
@@ -203,19 +204,18 @@ int 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) return TRUE;
+    uschar * bc = US b + ALIGNED_SIZEOF_STOREBLOCK;
+    if (US p >= bc && US p <= bc + b->length) return TRUE;
     }
 
 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) return TRUE;
+    uschar * bc = US b + ALIGNED_SIZEOF_STOREBLOCK;
+    if (US p >= bc && US p <= bc + b->length) return TRUE;
     }
 return FALSE;
 }
-#endif
 
 
 void
@@ -225,6 +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        *
@@ -848,6 +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");
 }