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elf: Remove version assert in check_match in elf/dl-lookup.c

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This case is detected early in the elf/dl-version.c consistency
checks.  (These checks could be disabled in the future to allow
the removal of symbol versioning from objects.)

Commit f0b2132b35 ("ld.so: Support moving versioned symbols between
sonames [BZ #24741]) removed another call to _dl_name_match_p.  The
_dl_check_caller function no longer exists, and the remaining calls
to _dl_name_match_p happen under the loader lock.  This means that
atomic accesses are no longer required for the l_libname list.  This
supersedes commit 395be7c218 ("elf: Fix data race in _dl_name_match_p
[BZ #21349]").
This commit is contained in:
Florian Weimer 2024-09-24 13:23:10 +02:00
parent 8f6a53eab8
commit bdaf500353
3 changed files with 5 additions and 36 deletions
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18
elf/dl-load.c
View File

@ -429,23 +429,7 @@ add_name_to_object (struct link_map *l, const char *name)
newname->name = memcpy (newname + 1, name, name_len); newname->name = memcpy (newname + 1, name, name_len);
newname->next = NULL; newname->next = NULL;
newname->dont_free = 0; newname->dont_free = 0;
/* CONCURRENCY NOTES: lastp->next = newname;
Make sure the initialization of newname happens before its address is
read from the lastp->next store below.
GL(dl_load_lock) is held here (and by other writers, e.g. dlclose), so
readers of libname_list->next (e.g. _dl_check_caller or the reads above)
can use that for synchronization, however the read in _dl_name_match_p
may be executed without holding the lock during _dl_runtime_resolve
(i.e. lazy symbol resolution when a function of library l is called).
The release MO store below synchronizes with the acquire MO load in
_dl_name_match_p. Other writes need to synchronize with that load too,
however those happen either early when the process is single threaded
(dl_main) or when the library is unloaded (dlclose) and the user has to
synchronize library calls with unloading. */
atomic_store_release (&lastp->next, newname);
} }
/* Standard search directories. */ /* Standard search directories. */

19
elf/dl-lookup.c
View File

@ -93,22 +93,9 @@ check_match (const char *const undef_name,
const ElfW(Half) *verstab = map->l_versyms; const ElfW(Half) *verstab = map->l_versyms;
if (version != NULL) if (version != NULL)
{ {
if (__glibc_unlikely (verstab == NULL)) /* If there is no version information, accept the symbol. This
{ can happen during symbol interposition. */
/* We need a versioned symbol but haven't found any. If if (__glibc_likely (verstab != NULL))
this is the object which is referenced in the verneed
entry it is a bug in the library since a symbol must
not simply disappear.
It would also be a bug in the object since it means that
the list of required versions is incomplete and so the
tests in dl-version.c haven't found a problem.*/
assert (version->filename == NULL
|| ! _dl_name_match_p (version->filename, map));
/* Otherwise we accept the symbol. */
}
else
{ {
/* We can match the version information or use the /* We can match the version information or use the
default one if it is not hidden. */ default one if it is not hidden. */

4
elf/dl-misc.c
View File

@ -75,9 +75,7 @@ _dl_name_match_p (const char *name, const struct link_map *map)
if (strcmp (name, runp->name) == 0) if (strcmp (name, runp->name) == 0)
return 1; return 1;
else else
/* Synchronize with the release MO store in add_name_to_object. runp = runp->next;
See CONCURRENCY NOTES in add_name_to_object in dl-load.c. */
runp = atomic_load_acquire (&runp->next);
return 0; return 0;
} }