Re: [PATCH] wcsmbs: Fix data race in __wcsmbs_clone_conv [BZ #24584]

[Florian Weimer <fweimer at redhat dot com>]

* Andreas Schwab:

> On Mai 20 2019, Florian Weimer <fweimer@redhat.com> wrote:
>
>> diff --git a/iconv/gconv_int.h b/iconv/gconv_int.h
>> index ea41d6feaa..9510102c07 100644
>> --- a/iconv/gconv_int.h
>> +++ b/iconv/gconv_int.h
>> @@ -45,7 +45,8 @@ struct __gconv_loaded_object
>>    const char *name;
>>  
>>    /* Reference counter for the db functionality.  If no conversion is
>> -     needed we unload the db library.  */
>> +     needed we unload the db library.  __gconv_lock is used to
>> +     synchronize updates to this field.  */
>>    int counter;
>
> That's struct __gconv_loaded_object.
>
>> @@ -223,12 +224,24 @@ __wcsmbs_clone_conv (struct gconv_fcts *copy)
>>    /* Copy the data.  */
>>    *copy = *orig;
>>  
>> -  /* Now increment the usage counters.
>> -     Note: This assumes copy->*_nsteps == 1.  */
>> +  /* Now increment the usage counters.  Note: This assumes
>> +     copy->*_nsteps == 1.  The current locale holds a reference, so it
>> +     is still there after acquiring the lock.  */
>> +
>> +  __libc_lock_lock (__gconv_lock);
>> +
>> +  bool overflow = false;
>>    if (copy->towc->__shlib_handle != NULL)
>> -    ++copy->towc->__counter;
>> +    overflow |= __builtin_add_overflow (copy->towc->__counter, 1,
>> +					&copy->towc->__counter);
>
> That's struct __gconv_step.

Thanks.  What about this patch?

Florian

wcsmbs: Fix data race in __wcsmbs_clone_conv [BZ #24584]

This also adds an overflow check and documents the synchronization
requirement in <gconv.h>.

2019-05-20  Florian Weimer  <fweimer@redhat.com>


	[BZ #24584]
	* wcsmbs/wcsmbsload.c (__wcsmbs_clone_conv): Acquire __gconv_lock
	before updating __counter field and release it afterwards.  Add
	overflow check.
	* iconv/gconv.h (struct __gconv_step): Mention synchronization
	requirement for __counter member.

diff --git a/iconv/gconv.h b/iconv/gconv.h
index 5ad26c06ac..7ce79bcbf6 100644
--- a/iconv/gconv.h
+++ b/iconv/gconv.h
@@ -86,6 +86,8 @@ struct __gconv_step
   struct __gconv_loaded_object *__shlib_handle;
   const char *__modname;
 
+  /* For internal use by glibc.  (Accesses to this member must occur
+     when the internal __gconv_lock mutex is acquired).  */
   int __counter;
 
   char *__from_name;
diff --git a/wcsmbs/wcsmbsload.c b/wcsmbs/wcsmbsload.c
index 5494d0a23e..e33a9c1312 100644
--- a/wcsmbs/wcsmbsload.c
+++ b/wcsmbs/wcsmbsload.c
@@ -20,6 +20,7 @@
 #include <langinfo.h>
 #include <limits.h>
 #include <stdlib.h>
+#include <stdio.h>
 #include <string.h>
 
 #include <locale/localeinfo.h>
@@ -223,12 +224,24 @@ __wcsmbs_clone_conv (struct gconv_fcts *copy)
   /* Copy the data.  */
   *copy = *orig;
 
-  /* Now increment the usage counters.
-     Note: This assumes copy->*_nsteps == 1.  */
+  /* Now increment the usage counters.  Note: This assumes
+     copy->*_nsteps == 1.  The current locale holds a reference, so it
+     is still there after acquiring the lock.  */
+
+  __libc_lock_lock (__gconv_lock);
+
+  bool overflow = false;
   if (copy->towc->__shlib_handle != NULL)
-    ++copy->towc->__counter;
+    overflow |= __builtin_add_overflow (copy->towc->__counter, 1,
+					&copy->towc->__counter);
   if (copy->tomb->__shlib_handle != NULL)
-    ++copy->tomb->__counter;
+    overflow |= __builtin_add_overflow (copy->tomb->__counter, 1,
+					&copy->tomb->__counter);
+  if (overflow)
+    __libc_fatal ("\
+Fatal glibc error: gconv module reference counter overflow\n");
+
+  __libc_lock_unlock (__gconv_lock);
 }