Issue #12839: Fix crash in zlib module due to version mismatch.

If the version of zlib used to compile the zlib module is incompatible
with the one that is actually linked in, then calls into zlib will fail.
This can leave attributes of the z_stream uninitialized, so we must take
care to avoid segfaulting by trying to use an invalid pointer.

Fix by Richard M. Tew.

diff --git a/Misc/ACKS b/Misc/ACKS
index 6f7d9d12511d23b96de1d5425d1aef7b2cd1556e..7096d728d2849297e9c25fdf7a2f7bd21844f53e 100644 (file)
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -874,6 +874,7 @@ Monty Taylor
 Amy Taylor
 Anatoly Techtonik
 Mikhail Terekhov
+Richard M. Tew
 Tobias Thelen
 James Thomas
 Robin Thomas

diff --git a/Misc/NEWS b/Misc/NEWS
index f6fe5b7014f7c1970bccc4d3402fc351d7b01ef9..23b336bb52bb704518600af65170be44912ea4e6 100644 (file)
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -22,6 +22,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #12839: Fix crash in zlib module due to version mismatch.
+  Fix by Richard M. Tew.
+
 - Issue #11657: Fix sending file descriptors over 255 over a multiprocessing
   Pipe.
 

diff --git a/Modules/zlibmodule.c b/Modules/zlibmodule.c
index ba0e59ce0641d2ab6d3154b9b611b89d76aa8eef..a1e605b3d2be391f3c9a80e1e28fa03a767a180a 100644 (file)
--- a/Modules/zlibmodule.c
+++ b/Modules/zlibmodule.c
@@ -52,7 +52,13 @@ typedef struct
 static void
 zlib_error(z_stream zst, int err, char *msg)
 {
-    const char *zmsg = zst.msg;
+    const char *zmsg = Z_NULL;
+    /* In case of a version mismatch, zst.msg won't be initialized.
+       Check for this case first, before looking at zst.msg. */
+    if (err == Z_VERSION_ERROR)
+        zmsg = "library version mismatch";
+    if (zmsg == Z_NULL)
+        zmsg = zst.msg;
     if (zmsg == Z_NULL) {
         switch (err) {
         case Z_BUF_ERROR: