Fix SIGSEGV when nokogiri is loaded before oci8

This bug was introduced in 2.2.13.

Author: kubo

NEWS

@@ -1,5 +1,13 @@
 # @markup markdown
 
+2.2.14 (2024-08-XX)
+===================
+
+Fixed issues
+------------
+
+- Fix SIGSEGV when nokogiri is loaded before oci8 (GH-263 - Linux only)
+
 2.2.13 (2024-07-27)
 ===================
 

ext/oci8/oci8lib.c

@@ -9,6 +9,7 @@
 #endif
 #if defined(HAVE_PLTHOOK) && !defined(WIN32)
 #include <dlfcn.h>
+#include <sys/mman.h>
 #include "plthook.h"
 #endif
 
@@ -135,6 +136,8 @@ static void rebind_internal_symbols(void)
     void **addr;
     const char *prefix;
     size_t prefix_len;
+    int prot;
+    size_t page_size = sysconf(_SC_PAGESIZE);
 
 #ifdef RTLD_FIRST
     flags |= RTLD_FIRST; /* for macOS */
@@ -161,7 +164,7 @@ static void rebind_internal_symbols(void)
         plthook_close(ph);
         return;
     }
-    while (plthook_enum(ph, &pos, &name, &addr) == 0) {
+    while (plthook_enum_with_prot(ph, &pos, &name, &addr, &prot) == 0) {
         void *funcaddr;
         if (prefix_len != 0) {
             if (strncmp(name, prefix, prefix_len) != 0) {
@@ -179,7 +182,17 @@ static void rebind_internal_symbols(void)
              * PLT entries are forcedly modified to point to itself not
              * to use functions in other libraries.
              */
+#define ALIGN_ADDR(addr) ((void*)((size_t)(addr) & ~(page_size - 1)))
+            if ((prot & PROT_WRITE) == 0) {
+                /* when the region containing addr isn't writable, make it writable temporarily */
+                if (mprotect(ALIGN_ADDR(addr), page_size, PROT_READ | PROT_WRITE) != 0) {
+                    continue;
+                }
+            }
             *addr = funcaddr;
+            if ((prot & PROT_WRITE) == 0) {
+                mprotect(ALIGN_ADDR(addr), page_size, prot);
+            }
         }
     }
     plthook_close(ph);

ext/oci8/plthook.h

@@ -59,8 +59,14 @@ int plthook_replace(plthook_t *plthook, const char *funcname, void *funcaddr, vo
 void plthook_close(plthook_t *plthook);
 const char *plthook_error(void);
 
+/* enumerate entries with memory protection information (bitwise-OR of PROT_READ, PROT_WRITE and PROT_EXEC)
+ *
+ * source: plthook_elf.c and plthook_osx.c
+ */
+int plthook_enum_with_prot(plthook_t *plthook, unsigned int *pos, const char **name_out, void ***addr_out, int *prot);
+
 #ifdef __cplusplus
-}; /* extern "C" */
+} /* extern "C" */
 #endif
 
 #endif