[v3,19/37] dlfcn: Failures after dlmopen should not terminate process [BZ #24772]

  Commit 9e78f6f6e7134a5f299cc8de77370218f8019237 ("Implement
_dl_catch_error, _dl_signal_error in libc.so [BZ #16628]") has the
side effect that distinct namespaces, as created by dlmopen, now have
separate implementations of the rtld exception mechanism.  This means
that the call to _dl_catch_error from libdl in a secondary namespace
does not actually install an exception handler because the
thread-local variable catch_hook in the libc.so copy in the secondary
namespace is distinct from that of the base namepace.  As a result, a
dlsym/dlopen/… failure in a secondary namespace terminates the process
with a dynamic linker error because it looks to the exception handler
mechanism as if no handler has been installed.

This commit restores GLRO (dl_catch_error) and uses it to set the
handler in the base namespace.
---
 dlfcn/dlerror.c               |  6 +++--
 elf/Makefile                  |  8 ++++++-
 elf/dl-error-skeleton.c       | 12 ++++++++++
 elf/rtld.c                    |  1 +
 elf/tst-dlmopen-dlerror-mod.c | 41 +++++++++++++++++++++++++++++++++++
 elf/tst-dlmopen-dlerror.c     | 37 +++++++++++++++++++++++++++++++
 sysdeps/generic/ldsodefs.h    |  9 ++++++++
 7 files changed, 111 insertions(+), 3 deletions(-)
 create mode 100644 elf/tst-dlmopen-dlerror-mod.c
 create mode 100644 elf/tst-dlmopen-dlerror.c
  

On 16/03/2021 14:30, Florian Weimer via Libc-alpha wrote:
> Commit 9e78f6f6e7134a5f299cc8de77370218f8019237 ("Implement
> _dl_catch_error, _dl_signal_error in libc.so [BZ #16628]") has the
> side effect that distinct namespaces, as created by dlmopen, now have
> separate implementations of the rtld exception mechanism.  This means
> that the call to _dl_catch_error from libdl in a secondary namespace
> does not actually install an exception handler because the
> thread-local variable catch_hook in the libc.so copy in the secondary
> namespace is distinct from that of the base namepace.  As a result, a
> dlsym/dlopen/… failure in a secondary namespace terminates the process
> with a dynamic linker error because it looks to the exception handler
> mechanism as if no handler has been installed.
> 
> This commit restores GLRO (dl_catch_error) and uses it to set the
> handler in the base namespace.

LGTM, thanks.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

> ---
>  dlfcn/dlerror.c               |  6 +++--
>  elf/Makefile                  |  8 ++++++-
>  elf/dl-error-skeleton.c       | 12 ++++++++++
>  elf/rtld.c                    |  1 +
>  elf/tst-dlmopen-dlerror-mod.c | 41 +++++++++++++++++++++++++++++++++++
>  elf/tst-dlmopen-dlerror.c     | 37 +++++++++++++++++++++++++++++++
>  sysdeps/generic/ldsodefs.h    |  9 ++++++++
>  7 files changed, 111 insertions(+), 3 deletions(-)
>  create mode 100644 elf/tst-dlmopen-dlerror-mod.c
>  create mode 100644 elf/tst-dlmopen-dlerror.c
> 
> diff --git a/dlfcn/dlerror.c b/dlfcn/dlerror.c
> index 48b4c25bea..947b7c10c6 100644
> --- a/dlfcn/dlerror.c
> +++ b/dlfcn/dlerror.c
> @@ -167,8 +167,10 @@ _dlerror_run (void (*operate) (void *), void *args)
>        result->errstring = NULL;
>      }
>  
> -  result->errcode = _dl_catch_error (&result->objname, &result->errstring,
> -				     &result->malloced, operate, args);
> +  result->errcode = GLRO (dl_catch_error) (&result->objname,
> +					   &result->errstring,
> +					   &result->malloced,
> +					   operate, args);
>  
>    /* If no error we mark that no error string is available.  */
>    result->returned = result->errstring == NULL;

Ok.

> diff --git a/elf/Makefile b/elf/Makefile
> index 936d4cf276..deb76aed99 100644
> --- a/elf/Makefile
> +++ b/elf/Makefile
> @@ -222,7 +222,8 @@ tests += restest1 preloadtest loadfail multiload origtest resolvfail \
>  	 tst-audit14 tst-audit15 tst-audit16 \
>  	 tst-single_threaded tst-single_threaded-pthread \
>  	 tst-tls-ie tst-tls-ie-dlmopen argv0test \
> -	 tst-glibc-hwcaps tst-glibc-hwcaps-prepend tst-glibc-hwcaps-mask
> +	 tst-glibc-hwcaps tst-glibc-hwcaps-prepend tst-glibc-hwcaps-mask \
> +	 tst-dlmopen-dlerror
>  #	 reldep9
>  tests-internal += loadtest unload unload2 circleload1 \
>  	 neededtest neededtest2 neededtest3 neededtest4 \
> @@ -344,6 +345,7 @@ modules-names = testobj1 testobj2 testobj3 testobj4 testobj5 testobj6 \
>  		libmarkermod2-1 libmarkermod2-2 \
>  		libmarkermod3-1 libmarkermod3-2 libmarkermod3-3 \
>  		libmarkermod4-1 libmarkermod4-2 libmarkermod4-3 libmarkermod4-4 \
> +		tst-ldconfig-ld-mod tst-dlmopen-dlerror-mod \
>  
>  # Most modules build with _ISOMAC defined, but those filtered out
>  # depend on internal headers.
> @@ -1580,6 +1582,10 @@ $(objpfx)tst-sonamemove-dlopen.out: \
>    $(objpfx)tst-sonamemove-runmod1.so \
>    $(objpfx)tst-sonamemove-runmod2.so
>  
> +$(objpfx)tst-dlmopen-dlerror: $(libdl)
> +$(objpfx)tst-dlmopen-dlerror-mod.so: $(libdl) $(libsupport)
> +$(objpfx)tst-dlmopen-dlerror.out: $(objpfx)tst-dlmopen-dlerror-mod.so
> +
>  # Override -z defs, so that we can reference an undefined symbol.
>  # Force lazy binding for the same reason.
>  LDFLAGS-tst-latepthreadmod.so = \

Ok.

> diff --git a/elf/dl-error-skeleton.c b/elf/dl-error-skeleton.c
> index 2fd62777cf..b699936c6e 100644
> --- a/elf/dl-error-skeleton.c
> +++ b/elf/dl-error-skeleton.c
> @@ -248,4 +248,16 @@ _dl_receive_error (receiver_fct fct, void (*operate) (void *), void *args)
>    catch_hook = old_catch;
>    receiver = old_receiver;
>  }
> +
> +/* Forwarder used for initializing GLRO (_dl_catch_error).  */
> +int
> +_rtld_catch_error (const char **objname, const char **errstring,
> +		   bool *mallocedp, void (*operate) (void *),
> +		   void *args)
> +{
> +  /* The reference to _dl_catch_error will eventually be relocated to
> +     point to the implementation in libc.so.  */
> +  return _dl_catch_error (objname, errstring, mallocedp, operate, args);
> +}
> +
>  #endif /* DL_ERROR_BOOTSTRAP */

Ok, but why change the usual prepend string to 'rtld'?

> diff --git a/elf/rtld.c b/elf/rtld.c
> index 94a00e2049..fd02438936 100644
> --- a/elf/rtld.c
> +++ b/elf/rtld.c
> @@ -368,6 +368,7 @@ struct rtld_global_ro _rtld_global_ro attribute_relro =
>      ._dl_lookup_symbol_x = _dl_lookup_symbol_x,
>      ._dl_open = _dl_open,
>      ._dl_close = _dl_close,
> +    ._dl_catch_error = _rtld_catch_error,
>      ._dl_tls_get_addr_soft = _dl_tls_get_addr_soft,
>  #ifdef HAVE_DL_DISCOVER_OSVERSION
>      ._dl_discover_osversion = _dl_discover_osversion

Ok.

> diff --git a/elf/tst-dlmopen-dlerror-mod.c b/elf/tst-dlmopen-dlerror-mod.c
> new file mode 100644
> index 0000000000..dcb94320b4
> --- /dev/null
> +++ b/elf/tst-dlmopen-dlerror-mod.c
> @@ -0,0 +1,41 @@
> +/* Check that dlfcn errors are reported properly after dlmopen.  Test module.
> +   Copyright (C) 2019 Free Software Foundation, Inc.

s/2019/2021.

> +   This file is part of the GNU C Library.
> +
> +   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 <dlfcn.h>
> +#include <stddef.h>
> +#include <support/check.h>
> +
> +/* Note: This object is not linked into the main program, so we cannot
> +   use delayed test failure reporting via TEST_VERIFY etc., and have
> +   to use FAIL_EXIT1 (or something else that calls exit).  */
> +
> +void
> +call_dlsym (void)
> +{
> +  void *ptr = dlsym (NULL, "does not exist");
> +  if (ptr != NULL)
> +    FAIL_EXIT1 ("dlsym did not fail as expected");
> +}
> +
> +void
> +call_dlopen (void)
> +{
> +  void *handle = dlopen ("tst-dlmopen-dlerror does not exist", RTLD_NOW);
> +  if (handle != NULL)
> +    FAIL_EXIT1 ("dlopen did not fail as expected");
> +}

Ok.

> diff --git a/elf/tst-dlmopen-dlerror.c b/elf/tst-dlmopen-dlerror.c
> new file mode 100644
> index 0000000000..65638f7f38
> --- /dev/null
> +++ b/elf/tst-dlmopen-dlerror.c
> @@ -0,0 +1,37 @@
> +/* Check that dlfcn errors are reported properly after dlmopen.
> +   Copyright (C) 2019 Free Software Foundation, Inc.

s/2019/2021.

> +   This file is part of the GNU C Library.
> +
> +   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 <stddef.h>
> +#include <support/check.h>
> +#include <support/xdlfcn.h>
> +
> +static int
> +do_test (void)
> +{
> +  void *handle = xdlmopen (LM_ID_NEWLM, "tst-dlmopen-dlerror-mod.so",
> +                           RTLD_NOW);
> +  void (*call_dlsym) (void) = xdlsym (handle, "call_dlsym");
> +  void (*call_dlopen) (void) = xdlsym (handle, "call_dlopen");
> +
> +  call_dlsym ();
> +  call_dlopen ();
> +
> +  return 0;
> +}
> +
> +#include <support/test-driver.c>

Ok.

> diff --git a/sysdeps/generic/ldsodefs.h b/sysdeps/generic/ldsodefs.h
> index ea3f7a69d0..b207f229c3 100644
> --- a/sysdeps/generic/ldsodefs.h
> +++ b/sysdeps/generic/ldsodefs.h
> @@ -662,6 +662,12 @@ struct rtld_global_ro
>    void *(*_dl_open) (const char *file, int mode, const void *caller_dlopen,
>  		     Lmid_t nsid, int argc, char *argv[], char *env[]);
>    void (*_dl_close) (void *map);
> +  /* libdl in a secondary namespace (after dlopen) must use
> +     _dl_catch_error from the main namespace, so it has to be
> +     exported in some way.  */
> +  int (*_dl_catch_error) (const char **objname, const char **errstring,
> +			  bool *mallocedp, void (*operate) (void *),
> +			  void *args);
>    void *(*_dl_tls_get_addr_soft) (struct link_map *);
>  #ifdef HAVE_DL_DISCOVER_OSVERSION
>    int (*_dl_discover_osversion) (void);
> @@ -900,6 +906,9 @@ extern int _dl_catch_error (const char **objname, const char **errstring,
>  			    void *args);
>  libc_hidden_proto (_dl_catch_error)
>  
> +/* Used for initializing GLRO (_dl_catch_error).  */
> +extern __typeof__ (_dl_catch_error) _rtld_catch_error attribute_hidden;
> +
>  /* Call OPERATE (ARGS).  If no error occurs, set *EXCEPTION to zero.
>     Otherwise, store a copy of the raised exception in *EXCEPTION,
>     which has to be freed by _dl_exception_free.  As a special case, if
> 

Ok.
  

* Adhemerval Zanella:

>> diff --git a/elf/dl-error-skeleton.c b/elf/dl-error-skeleton.c
>> index 2fd62777cf..b699936c6e 100644
>> --- a/elf/dl-error-skeleton.c
>> +++ b/elf/dl-error-skeleton.c
>> @@ -248,4 +248,16 @@ _dl_receive_error (receiver_fct fct, void (*operate) (void *), void *args)
>>    catch_hook = old_catch;
>>    receiver = old_receiver;
>>  }
>> +
>> +/* Forwarder used for initializing GLRO (_dl_catch_error).  */
>> +int
>> +_rtld_catch_error (const char **objname, const char **errstring,
>> +		   bool *mallocedp, void (*operate) (void *),
>> +		   void *args)
>> +{
>> +  /* The reference to _dl_catch_error will eventually be relocated to
>> +     point to the implementation in libc.so.  */
>> +  return _dl_catch_error (objname, errstring, mallocedp, operate, args);
>> +}
>> +
>>  #endif /* DL_ERROR_BOOTSTRAP */
>
> Ok, but why change the usual prepend string to 'rtld'?

_dl_catch_error is already taken.

Thanks,
Florian