For some reason only dlopen failure caused dtv gaps to be reused.
It is possible that the intent was to never reuse modids for a
different module, but after dlopen failure all gaps are reused
not just the ones caused by the unfinished dlopened.
So the code has to handle reused modids already which seems to
work, however the data races at thread creation and tls access
(see bug 19329 and bug 27111) may be more severe if slots are
reused so this is scheduled after those fixes. I think fixing
the races are not simpler if reuse is disallowed and reuse has
other benefits, so set GL(dl_tls_dtv_gaps) whenever entries are
removed from the middle of the slotinfo list. The value does
not have to be correct: incorrect true value causes the next
modid query to do a slotinfo walk, incorrect false will leave
gaps and new entries are added at the end.
Fixes bug 27135.
Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
This is a follow up patch to the fix for bug 19329. This adds relaxed
MO atomics to accesses that were previously data races but are now
race conditions, and where relaxed MO is sufficient.
The race conditions all follow the pattern that the write is behind the
dlopen lock, but a read can happen concurrently (e.g. during tls access)
without holding the lock. For slotinfo entries the read value only
matters if it reads from a synchronized write in dlopen or dlclose,
otherwise the related dtv entry is not valid to access so it is fine
to leave it in an inconsistent state. The same applies for
GL(dl_tls_max_dtv_idx) and GL(dl_tls_generation), but there the
algorithm relies on the fact that the read of the last synchronized
write is an increasing value.
Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
I used these shell commands:
../glibc/scripts/update-copyrights $PWD/../gnulib/build-aux/update-copyright
(cd ../glibc && git commit -am"[this commit message]")
and then ignored the output, which consisted lines saying "FOO: warning:
copyright statement not found" for each of 6694 files FOO.
I then removed trailing white space from benchtests/bench-pthread-locks.c
and iconvdata/tst-iconv-big5-hkscs-to-2ucs4.c, to work around this
diagnostic from Savannah:
remote: *** pre-commit check failed ...
remote: *** error: lines with trailing whitespace found
remote: error: hook declined to update refs/heads/master
The auditing interface identifies namespaces by their first loaded
module. Once the namespace is empty, it is no longer possible to signal
LA_ACT_CONSISTENT for it because the first loaded module is already gone
at that point.
Reviewed-by: Carlos O'Donell <carlos@redhat.com>
We should clear GL(dl_initfirst) when freeing its link_map memory.
Tested on Fedora 31/x86-64 with CET.
Reviewed-by: Florian Weimer <fweimer@redhat.com>
Commit a2e8aa0d9e ("Block signals during
the initial part of dlopen") was deemed necessary because of
read-modify-write operations like the one in add_dependency in
elf/dl-lookup.c. In the old code, we check for any kind of NODELETE
status and bail out:
/* Redo the NODELETE check, as when dl_load_lock wasn't held
yet this could have changed. */
if (map->l_nodelete != link_map_nodelete_inactive)
goto out;
And then set pending status (during relocation):
if (flags & DL_LOOKUP_FOR_RELOCATE)
map->l_nodelete = link_map_nodelete_pending;
else
map->l_nodelete = link_map_nodelete_active;
If a signal arrives during relocation and the signal handler, through
lazy binding, adds a global scope dependency on the same map, it will
set map->l_nodelete to link_map_nodelete_active. This will be
overwritten with link_map_nodelete_pending by the dlopen relocation
code.
To avoid such problems in relation to the l_nodelete member, this
commit introduces two flags for active NODELETE status (irrevocable)
and pending NODELETE status (revocable until activate_nodelete is
invoked). As a result, NODELETE processing in dlopen does not
introduce further reasons why lazy binding from signal handlers
is unsafe during dlopen, and a subsequent commit can remove signal
blocking from dlopen.
This does not address pre-existing issues (unrelated to the NODELETE
changes) which make lazy binding in a signal handler during dlopen
unsafe, such as the use of malloc in both cases.
Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Reviewed-by: Carlos O'Donell <carlos@redhat.com>
This introduces a “pending NODELETE” state in the link map, which is
flipped to the persistent NODELETE state late in dlopen, via
activate_nodelete. During initial relocation, symbol binding
records pending NODELETE state only. dlclose ignores pending NODELETE
state. Taken together, this results that a partially completed dlopen
is rolled back completely because new NODELETE mappings are unloaded.
Tested on x86_64-linux-gnu and i386-linux-gnu.
Change-Id: Ib2a3d86af6f92d75baca65431d74783ee0dbc292
If a lazy binding failure happens during the execution of an ELF
constructor or destructor, the dynamic loader catches the error
and reports it using the dlerror mechanism. This is undesirable
because there could be other constructors and destructors that
need processing (which are skipped), and the process is in an
inconsistent state at this point. Therefore, we have to issue
a fatal dynamic loader error error and terminate the process.
Note that the _dl_catch_exception in _dl_open is just an inner catch,
to roll back some state locally. If called from dlopen, there is
still an outer catch, which is why calling _dl_init via call_dl_init
and a no-exception is required and cannot be avoiding by moving the
_dl_init call directly into _dl_open.
_dl_fini does not need changes because it does not install an error
handler, so errors are already fatal there.
Change-Id: I6b1addfe2e30f50a1781595f046f44173db9491a
To improve GCC 10 compatibility, it is necessary to remove the l_audit
zero-length array from the end of struct link_map. In preparation of
that, this commit introduces an accessor function for the audit state,
so that it is possible to change the representation of the audit state
without adjusting the code that accesses it.
Tested on x86_64-linux-gnu. Built on i686-gnu.
Change-Id: Id815673c29950fc011ae5301d7cde12624f658df
Combine the four places where link maps are sorted into a single function.
This also moves the logic to skip the first map (representing the main
binary) to the callers.
There is at least one use case where during exit a library destructor
might call dlclose() on a valid handle and have it fail with an
assertion. We must allow this case, it is a valid handle, and dlclose()
should not fail with an assert. In the future we might be able to return
an error that the dlclose() could not be completed because the opened
library has already been unloaded and destructors have run as part of
exit processing.
For more details see:
https://www.sourceware.org/ml/libc-alpha/2016-12/msg00859.html
This change moves the main implementation of _dl_catch_error,
_dl_signal_error to libc.so, where TLS variables can be used
directly. This removes a writable function pointer from the
rtld_global variable.
For use during initial relocation, minimal implementations of these
functions are provided in ld.so. These are eventually interposed
by the libc.so implementations. This is implemented by compiling
elf/dl-error-skeleton.c twice, via elf/dl-error.c and
elf/dl-error-minimal.c.
As a side effect of this change, the static version of dl-error.c
no longer includes support for the
_dl_signal_cerror/_dl_receive_error mechanism because it is only
used in ld.so.
https://sourceware.org/bugzilla/show_bug.cgi?id=18778
If dlopen fails to load an object that has triggered loading libpthread it
causes ld.so to unload libpthread because its DF_1_NODELETE flags has been
forcefully cleared. The next call to __rtdl_unlock_lock_recursive will crash
since pthread_mutex_unlock no longer exists.
This patch moves l->l_flags_1 &= ~DF_1_NODELETE out of loop through all loaded
libraries and performs the action only on inconsistent one.
[BZ #18778]
* elf/Makefile (tests): Add Add tst-nodelete2.
(modules-names): Add tst-nodelete2mod.
(tst-nodelete2mod.so-no-z-defs): New.
($(objpfx)tst-nodelete2): Likewise.
($(objpfx)tst-nodelete2.out): Likewise.
(LDFLAGS-tst-nodelete2): Likewise.
* elf/dl-close.c (_dl_close_worker): Move DF_1_NODELETE clearing
out of loop through all loaded libraries.
* elf/tst-nodelete2.c: New file.
* elf/tst-nodelete2mod.c: Likewise.
When an TLS destructor is registered, we set the DF_1_NODELETE flag to
signal that the object should not be destroyed. We then clear the
DF_1_NODELETE flag when all destructors are called, which is wrong -
the flag could have been set by other means too.
This patch replaces this use of the flag by using l_tls_dtor_count
directly to determine whether it is safe to unload the object. This
change has the added advantage of eliminating the lock taking when
calling the destructors, which could result in a deadlock. The patch
also fixes the test case tst-tls-atexit - it was making an invalid
dlclose call, which would just return an error silently.
I have also added a detailed note on concurrency which also aims to
justify why I chose the semantics I chose for accesses to
l_tls_dtor_count. Thanks to Torvald for his help in getting me
started on this and (literally) teaching my how to approach the
problem.
Change verified on x86_64; the test suite does not show any
regressions due to the patch.
ChangeLog:
[BZ #18657]
* elf/dl-close.c (_dl_close_worker): Don't unload DSO if there
are pending TLS destructor calls.
* include/link.h (struct link_map): Add concurrency note for
L_TLS_DTOR_COUNT.
* stdlib/cxa_thread_atexit_impl.c (__cxa_thread_atexit_impl):
Don't touch the link map flag. Atomically increment
l_tls_dtor_count.
(__call_tls_dtors): Atomically decrement l_tls_dtor_count.
Avoid taking the load lock and don't touch the link map flag.
* stdlib/tst-tls-atexit-nodelete.c: New test case.
* stdlib/Makefile (tests): Use it.
* stdlib/tst-tls-atexit.c (do_test): dlopen
tst-tls-atexit-lib.so again before dlclose. Add conditionals
to allow tst-tls-atexit-nodelete test case to use it.
https://sourceware.org/bugzilla/show_bug.cgi?id=17833
I've a shared library that contains both undefined and unique symbols.
Then I try to call the following sequence of dlopen:
1. dlopen("./libfoo.so", RTLD_NOW)
2. dlopen("./libfoo.so", RTLD_LAZY | RTLD_GLOBAL)
First dlopen call terminates with error because of undefined symbols,
but STB_GNU_UNIQUE ones set DF_1_NODELETE flag and hence block library
in the memory.
The library goes into inconsistent state as several structures remain
uninitialized. For instance, relocations for GOT table were not performed.
By the time of second dlopen call this library looks like as it would be
fully initialized but this is not true: any call through incorrect GOT
table leads to segmentation fault. On some systems this inconsistency
triggers assertions in the dynamic linker.
This patch adds a parameter to _dl_close_worker to implement forced object
deletion in case of dlopen() failure:
1. Clears DF_1_NODELETE bit if forced, to allow library to be removed from
memory.
2. For each unique symbol that is defined in this object clears
appropriate entry in _ns_unique_sym_table.
[BZ #17833]
* elf/Makefile (tests): Add tst-nodelete.
(modules-names): Add tst-nodelete-uniquemod.
(tst-nodelete-uniquemod.so-no-z-defs): New.
(tst-nodelete-rtldmod.so-no-z-defs): Likewise.
(tst-nodelete-zmod.so-no-z-defs): Likewise.
($(objpfx)tst-nodelete): Likewise.
($(objpfx)tst-nodelete.out): Likewise.
(LDFLAGS-tst-nodelete): Likewise.
(LDFLAGS-tst-nodelete-zmod.so): Likewise.
* elf/dl-close.c (_dl_close_worker): Add a parameter to
implement forced object deletion.
(_dl_close): Pass false to _dl_close_worker.
* elf/dl-open.c (_dl_open): Pass true to _dl_close_worker.
* elf/tst-nodelete.cc: New file.
* elf/tst-nodeletelib.cc: Likewise.
* elf/tst-znodeletelib.cc: Likewise.
* include/dlfcn.h (_dl_close_worker): Add a new parameter.
Fixes to address issues from BZ #15022 resolution, as follows:
* TLS updates to csu/libc-tls.c -- we now have a proper main map, so
there's no longer a need to create a separate fake one to keep TLS
structures,
* random updates to elf/dl-close.c -- LM_ID_BASE is now a valid name
space ID for static executables as well, so assert that we don't
unload the main map. Similarly dl_nns isn't supposed to be 0 for
static executables anymore,
* actual BZ #16046 fix to elf/dl-iteratephdr.c -- the dl_iterate_phdr
special function for static executables isn't needed anymore, provided
that l_phdr and l_phnum members of the main map have been properly
initialized (done in _dl_non_dynamic_init in elf/dl-support.c now),
* ld.so.cache loader update to elf/dl-load.c --
GL(dl_ns)[LM_ID_BASE]._ns_loaded is now always initialized in static
executables so can become the fallback loader map to check for
DF_1_NODEFLIB, provided that the l_flags_1 member of the main map has
been properly initialized (done in elf/dl-support.c now); this also
ensures previous semantics elsewhere in elf/dl-load.c,
* matching updates to elf/dl-support.c -- to complement the two fixes
above.
On hppa and ia64, the macro DL_AUTO_FUNCTION_ADDRESS() uses the
variable fptr[2] in it's own scope.
The content of fptr[] is thus undefined right after the macro exits.
Newer gcc's (>= 4.7) reuse the stack space of this variable triggering
a segmentation fault in dl-init.c:69.
To fix this we rewrite the macros to make the call directly to init
and fini without needing to pass back a constructed function pointer.
The algorithm for scanning dependencies upon dlclose is
less than immediately obvious. This patch adds two bits
of comments that explain why you start the dependency
search at l_initfini[1], and why you need to restart
the search.
---
2013-05-09 Carlos O'Donell <carlos@redhat.com>
* elf/dl-close.c (_dl_close_worker): Add comments.
When unmapping the first object in a namespace, the runtime linker
did not update the externally visible pointer. This resulted in
debuggers seeing pointers to memory that had been freed.
[BZ #13579] Do not free l_initfini and allow it to be reused
on subsequent dl_open calls for the same library. This fixes
the invalid memory access in do_lookup_x when the previously
free'd l_initfini was accessed through l_searchlist when a
library had been opened for the second time.
* elf/dl-close.c (_dl_close): Check for it.
* elf/dl-reloc.c (CHECK_STATIC_TLS): Likewise.
(_dl_allocate_static_tls): Likewise.
* elf/dl-tls.c (_dl_allocate_tls_init): Likewise.
(__tls_get_addr): Protect from race conditions in setting l_tls_offset
to it.
* elf/tst-tls16.c: New file.
* elf/tst-tlsmod16a.c: New file.
* elf/tst-tlsmod16b.c: New file.
* elf/Makefile: Add rules to build and run tst-tls16.
void * pointers instead of struct link_map **.
(_dl_scope_free): Change argument type to void *.
* include/link.h (struct link_map): Change type of l_reldeps
to struct link_map_reldeps, move l_reldepsact into that
struct too.
* elf/dl-deps.c: Include atomic.h.
(_dl_map_object_deps): Only change l->l_initfini when it is
fully populated, use _dl_scope_free for freeing it. Optimize
removal of libs from reldeps by using l_reserved flag, when
some removal is needed, allocate a new list instead of
reallocating and free the old with _dl_scope_free. Adjust
for l_reldeps and l_reldepsact changes.
* elf/dl-lookup.c (add_dependency): Likewise. Reorganize to allow
searching in l_initfini and l_reldeps without holding dl_load_lock.
* elf/dl-fini.c (_dl_sort_fini): Adjust for l_reldeps and
l_reldepsact changes.
* elf/dl-close.c (_dl_close_worker): Likewise.
* elf/dl-open.c (_dl_scope_free): Change argument type to void *.
