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From: Florian Weimer <fw@sourceware.org> To: glibc-cvs@sourceware.org Subject: [glibc] elf: Make more functions available for binding during dlclose (bug 30425) Date: Tue, 30 May 2023 11:26:07 +0000 (GMT) [thread overview] Message-ID: <20230530112607.285F63856DE6@sourceware.org> (raw) https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=d0f07f7df8d9758c838674b70144ac73bcbd1634 commit d0f07f7df8d9758c838674b70144ac73bcbd1634 Author: Florian Weimer <fweimer@redhat.com> Date: Tue May 30 13:25:50 2023 +0200 elf: Make more functions available for binding during dlclose (bug 30425) Previously, after destructors for a DSO have been invoked, ld.so refused to bind against that DSO in all cases. Relax this restriction somewhat if the referencing object is itself a DSO that is being unloaded. This assumes that the symbol reference is not going to be stored anywhere. The situation in the test case can arise fairly easily with C++ and objects that are built with different optimization levels and therefore define different functions with vague linkage. Reviewed-by: Carlos O'Donell <carlos@redhat.com> Diff: --- elf/Makefile | 8 ++++++++ elf/dl-lookup.c | 21 +++++++++++++++++-- elf/tst-dlclose-lazy-mod1.c | 36 +++++++++++++++++++++++++++++++++ elf/tst-dlclose-lazy-mod2.c | 49 +++++++++++++++++++++++++++++++++++++++++++++ elf/tst-dlclose-lazy.c | 47 +++++++++++++++++++++++++++++++++++++++++++ 5 files changed, 159 insertions(+), 2 deletions(-) diff --git a/elf/Makefile b/elf/Makefile index 264737110b..3bfc305d98 100644 --- a/elf/Makefile +++ b/elf/Makefile @@ -396,6 +396,7 @@ tests += \ tst-debug1 \ tst-deep1 \ tst-dl-is_dso \ + tst-dlclose-lazy \ tst-dlmodcount \ tst-dlmopen-dlerror \ tst-dlmopen-gethostbyname \ @@ -816,6 +817,8 @@ modules-names += \ tst-dl_find_object-mod7 \ tst-dl_find_object-mod8 \ tst-dl_find_object-mod9 \ + tst-dlclose-lazy-mod1 \ + tst-dlclose-lazy-mod2 \ tst-dlmopen-dlerror-mod \ tst-dlmopen-gethostbyname-mod \ tst-dlmopen-twice-mod1 \ @@ -3001,3 +3004,8 @@ $(objpfx)tst-sprof-basic.out: tst-sprof-basic.sh $(objpfx)tst-sprof-basic '$(run-program-env)' > $@; \ $(evaluate-test) generated += tst-sprof-mod.so.profile + +LDFLAGS-tst-dlclose-lazy-mod1.so = -Wl,-z,lazy,--no-as-needed +$(objpfx)tst-dlclose-lazy-mod1.so: $(objpfx)tst-dlclose-lazy-mod2.so +$(objpfx)tst-dlclose-lazy.out: \ + $(objpfx)tst-dlclose-lazy-mod1.so $(objpfx)tst-dlclose-lazy-mod2.so diff --git a/elf/dl-lookup.c b/elf/dl-lookup.c index 05f36a2507..a8f48fed12 100644 --- a/elf/dl-lookup.c +++ b/elf/dl-lookup.c @@ -366,8 +366,25 @@ do_lookup_x (const char *undef_name, unsigned int new_hash, if ((type_class & ELF_RTYPE_CLASS_COPY) && map->l_type == lt_executable) continue; - /* Do not look into objects which are going to be removed. */ - if (map->l_removed) + /* Do not look into objects which are going to be removed, + except when the referencing object itself is being removed. + + The second part covers the situation when an object lazily + binds to another object while running its destructor, but the + destructor of the other object has already run, so that + dlclose has set l_removed. It may not always be obvious how + to avoid such a scenario to programmers creating DSOs, + particularly if C++ vague linkage is involved and triggers + symbol interposition. + + Accepting these to-be-removed objects makes the lazy and + BIND_NOW cases more similar. (With BIND_NOW, the symbol is + resolved early, before the destructor call, so the issue does + not arise.). Behavior matches the constructor scenario: the + implementation allows binding to symbols of objects whose + constructors have not run. In fact, not doing this would be + mostly incompatible with symbol interposition. */ + if (map->l_removed && !(undef_map != NULL && undef_map->l_removed)) continue; /* Print some debugging info if wanted. */ diff --git a/elf/tst-dlclose-lazy-mod1.c b/elf/tst-dlclose-lazy-mod1.c new file mode 100644 index 0000000000..8439dc1925 --- /dev/null +++ b/elf/tst-dlclose-lazy-mod1.c @@ -0,0 +1,36 @@ +/* Lazy binding during dlclose. Directly loaded module. + Copyright (C) 2023 Free Software Foundation, Inc. + 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 + <https://www.gnu.org/licenses/>. */ + +/* This function is called from exported_function below. It is only + defined in this module. The weak attribute mimics how G++ + implements vague linkage for C++. */ +void __attribute__ ((weak)) +lazily_bound_exported_function (void) +{ +} + +/* Called from tst-dlclose-lazy-mod2.so. */ +void +exported_function (int call_it) +{ + if (call_it) + /* Previous to the fix this would crash when called during dlclose + since symbols from the DSO were no longer available for binding + (bug 30425) after the DSO started being closed by dlclose. */ + lazily_bound_exported_function (); +} diff --git a/elf/tst-dlclose-lazy-mod2.c b/elf/tst-dlclose-lazy-mod2.c new file mode 100644 index 0000000000..767f69ffdb --- /dev/null +++ b/elf/tst-dlclose-lazy-mod2.c @@ -0,0 +1,49 @@ +/* Lazy binding during dlclose. Indirectly loaded module. + Copyright (C) 2023 Free Software Foundation, Inc. + 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 + <https://www.gnu.org/licenses/>. */ + +#include <stdio.h> +#include <stdlib.h> + +void +exported_function (int ignored) +{ + /* This function is interposed from tst-dlclose-lazy-mod1.so and + thus never called. */ + abort (); +} + +static void __attribute__ ((constructor)) +init (void) +{ + puts ("info: tst-dlclose-lazy-mod2.so constructor called"); + + /* Trigger lazy binding to the definition in + tst-dlclose-lazy-mod1.so, but not for + lazily_bound_exported_function in that module. */ + exported_function (0); +} + +static void __attribute__ ((destructor)) +fini (void) +{ + puts ("info: tst-dlclose-lazy-mod2.so destructor called"); + + /* Trigger the lazily_bound_exported_function call in + exported_function in tst-dlclose-lazy-mod1.so. */ + exported_function (1); +} diff --git a/elf/tst-dlclose-lazy.c b/elf/tst-dlclose-lazy.c new file mode 100644 index 0000000000..976a6bb6f6 --- /dev/null +++ b/elf/tst-dlclose-lazy.c @@ -0,0 +1,47 @@ +/* Test lazy binding during dlclose (bug 30425). + Copyright (C) 2023 Free Software Foundation, Inc. + 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 + <https://www.gnu.org/licenses/>. */ + +/* This test re-creates a situation that can arise naturally for C++ + applications due to the use of vague linkage and differences in the + set of compiler-emitted functions. A function in + tst-dlclose-lazy-mod1.so (exported_function) interposes a function + in tst-dlclose-lazy-mod2.so. This function is called from the + destructor in tst-dlclose-lazy-mod2.so, after the destructor for + tst-dlclose-lazy-mod1.so has already completed. Prior to the fix + for bug 30425, this would lead to a lazy binding failure in + tst-dlclose-lazy-mod1.so because dlclose had already marked the DSO + as unavailable for binding (by setting l_removed). */ + +#include <dlfcn.h> +#include <support/xdlfcn.h> +#include <support/check.h> + +int +main (void) +{ + /* Load tst-dlclose-lazy-mod1.so, indirectly loading + tst-dlclose-lazy-mod2.so. */ + void *handle = xdlopen ("tst-dlclose-lazy-mod1.so", RTLD_GLOBAL | RTLD_LAZY); + + /* Invoke the destructor of tst-dlclose-lazy-mod2.so, which calls + into tst-dlclose-lazy-mod1.so after its destructor has been + called. */ + xdlclose (handle); + + return 0; +}
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