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Fix recursive dlopen.
The ability to recursively call dlopen is useful for malloc implementations that wish to load other dynamic modules that implement reentrant/AS-safe functions to use in their own implementation. Given that a user malloc implementation may be called by an ongoing dlopen to allocate memory the user malloc implementation interrupts dlopen and if it calls dlopen again that's a reentrant call. This patch fixes the issues with the ld.so.cache mapping and the _r_debug assertion which prevent this from working as expected. See: https://sourceware.org/ml/libc-alpha/2014-12/msg00446.html
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Carlos O'Donell
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Jan 21, 2015
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,10 @@ | ||
| /* Provide a dummy DSO for tst-rec-dlopen to use. */ | ||
| #include <stdio.h> | ||
| #include <stdlib.h> | ||
|
|
||
| int | ||
| dummy1 (void) | ||
| { | ||
| printf ("Called dummy1()\n"); | ||
| return 1; | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,13 @@ | ||
| /* Provide a dummy DSO for tst-rec-dlopen to use. */ | ||
| #include <stdio.h> | ||
| #include <stdlib.h> | ||
|
|
||
| int | ||
| dummy2 (void) | ||
| { | ||
| printf ("Called dummy2()\n"); | ||
| /* If the outer dlopen is not dummy1 (becuase of some error) | ||
| then tst-rec-dlopen will see a value of -1 as the returned | ||
| result and fail. */ | ||
| return -1; | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,144 @@ | ||
| /* Test recursive dlopen using malloc hooks. | ||
| Copyright (C) 1998-2014 Free Software Foundation, Inc. | ||
| This file is part of the GNU C Library. | ||
| Contributed by Ulrich Drepper <drepper@cygnus.com>, 1998. | ||
| The GNU C Library is free software; you can redistribute it and/or | ||
| modify it under the terms of the GNU Lesser General Public | ||
| License as published by the Free Software Foundation; either | ||
| version 2.1 of the License, or (at your option) any later version. | ||
| The GNU C Library is distributed in the hope that it will be useful, | ||
| but WITHOUT ANY WARRANTY; without even the implied warranty of | ||
| MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | ||
| Lesser General Public License for more details. | ||
| You should have received a copy of the GNU Lesser General Public | ||
| License along with the GNU C Library; if not, see | ||
| <http://www.gnu.org/licenses/>. */ | ||
|
|
||
| #include <stdio.h> | ||
| #include <stdlib.h> | ||
| #include <malloc.h> | ||
| #include <dlfcn.h> | ||
|
|
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| #define DSO "moddummy1.so" | ||
| #define FUNC "dummy1" | ||
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| #define DSO1 "moddummy2.so" | ||
| #define FUNC1 "dummy2" | ||
|
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| /* Result of the called function. */ | ||
| int func_result; | ||
|
|
||
| /* Prototype for my hook. */ | ||
| void *custom_malloc_hook (size_t, const void *); | ||
|
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| /* Pointer to old malloc hooks. */ | ||
| void *(*old_malloc_hook) (size_t, const void *); | ||
|
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| /* Call function func_name in DSO dso_name via dlopen. */ | ||
| void | ||
| call_func (const char *dso_name, const char *func_name) | ||
| { | ||
| int ret; | ||
| void *dso; | ||
| int (*func) (void); | ||
| char *err; | ||
|
|
||
| /* Open the DSO. */ | ||
| dso = dlopen (dso_name, RTLD_NOW|RTLD_GLOBAL); | ||
| if (dso == NULL) | ||
| { | ||
| err = dlerror (); | ||
| fprintf (stderr, "%s\n", err); | ||
| exit (1); | ||
| } | ||
| /* Clear any errors. */ | ||
| dlerror (); | ||
|
|
||
| /* Lookup func. */ | ||
| *(void **) (&func) = dlsym (dso, func_name); | ||
| if (func == NULL) | ||
| { | ||
| err = dlerror (); | ||
| if (err != NULL) | ||
| { | ||
| fprintf (stderr, "%s\n", err); | ||
| exit (1); | ||
| } | ||
| } | ||
| /* Call func. */ | ||
| func_result = (*func) (); | ||
|
|
||
| /* Close the library and look for errors too. */ | ||
| ret = dlclose (dso); | ||
| if (ret != 0) | ||
| { | ||
| err = dlerror (); | ||
| fprintf (stderr, "%s\n", err); | ||
| exit (1); | ||
| } | ||
|
|
||
| } | ||
|
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| /* Empty hook that does nothing. */ | ||
| void * | ||
| custom_malloc_hook (size_t size, const void *caller) | ||
| { | ||
| void *result; | ||
| /* Restore old hooks. */ | ||
| __malloc_hook = old_malloc_hook; | ||
| /* First call a function in another library via dlopen. */ | ||
| call_func (DSO1, FUNC1); | ||
| /* Called recursively. */ | ||
| result = malloc (size); | ||
| /* Restore new hooks. */ | ||
| __malloc_hook = custom_malloc_hook; | ||
| return result; | ||
| } | ||
|
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||
| static int | ||
| do_test (void) | ||
| { | ||
| /* Save old hook. */ | ||
| old_malloc_hook = __malloc_hook; | ||
| /* Install new hook. */ | ||
| __malloc_hook = custom_malloc_hook; | ||
|
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| /* Bug 17702 fixes two things: | ||
| * A recursive dlopen unmapping the ld.so.cache. | ||
| * An assertion that _r_debug is RT_CONSISTENT at entry to dlopen. | ||
| We can only test the latter. Testing the former requires modifying | ||
| ld.so.conf to cache the dummy libraries, then running ldconfig, | ||
| then run the test. If you do all of that (and glibc's test | ||
| infrastructure doesn't support that yet) then the test will | ||
| SEGFAULT without the fix. If you don't do that, then the test | ||
| will abort because of the assert described in detail below. */ | ||
| call_func (DSO, FUNC); | ||
|
|
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| /* Restore old hook. */ | ||
| __malloc_hook = old_malloc_hook; | ||
|
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| /* The function dummy2() is called by the malloc hook. Check to | ||
| see that it was called. This ensures the second recursive | ||
| dlopen happened and we called the function in that library. | ||
| Before the fix you either get a SIGSEGV when accessing mmap'd | ||
| ld.so.cache data or an assertion failure about _r_debug not | ||
| beint RT_CONSISTENT. We don't test for the SIGSEGV since it | ||
| would require finding moddummy1 or moddummy2 in the cache and | ||
| we don't have any infrastructure to test that, but the _r_debug | ||
| assertion triggers. */ | ||
| printf ("Returned result is %d\n", func_result); | ||
| if (func_result <= 0) | ||
| { | ||
| printf ("FAIL: Function call_func() not called.\n"); | ||
| exit (1); | ||
| } | ||
|
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| printf ("PASS: Function call_func() called more than once.\n"); | ||
| return 0; | ||
| } | ||
|
|
||
| #define TEST_FUNCTION do_test () | ||
| #include "../test-skeleton.c" |
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