glibc/glibc-RHEL-39992-1.patch
Patsy Griffin 45033701c6 elf: Avoid some free (NULL) calls in _dl_update_slotinfo
elf: Support recursive use of dynamic TLS in interposed malloc

Resolves: RHEL-39992
2024-07-11 16:01:24 -04:00

44 lines
1.8 KiB
Diff

commit afe42e935b3ee97bac9a7064157587777259c60e
Author: Florian Weimer <fweimer@redhat.com>
Date: Mon Jun 3 10:49:40 2024 +0200
elf: Avoid some free (NULL) calls in _dl_update_slotinfo
This has been confirmed to work around some interposed mallocs. Here
is a discussion of the impact test ust/libc-wrapper/test_libc-wrapper
in lttng-tools:
New TLS usage in libgcc_s.so.1, compatibility impact
<https://inbox.sourceware.org/libc-alpha/8734v1ieke.fsf@oldenburg.str.redhat.com/>
Reportedly, this patch also papers over a similar issue when tcmalloc
2.9.1 is not compiled with -ftls-model=initial-exec. Of course the
goal really should be to compile mallocs with the initial-exec TLS
model, but this commit appears to be a useful interim workaround.
Fixes commit d2123d68275acc0f061e73d5f86ca504e0d5a344 ("elf: Fix slow
tls access after dlopen [BZ #19924]").
Reviewed-by: Carlos O'Donell <carlos@redhat.com>
diff --git a/elf/dl-tls.c b/elf/dl-tls.c
index 7b3dd9ab60..670dbc42fc 100644
--- a/elf/dl-tls.c
+++ b/elf/dl-tls.c
@@ -819,7 +819,14 @@ _dl_update_slotinfo (unsigned long int req_modid, size_t new_gen)
dtv entry free it. Note: this is not AS-safe. */
/* XXX Ideally we will at some point create a memory
pool. */
- free (dtv[modid].pointer.to_free);
+ /* Avoid calling free on a null pointer. Some mallocs
+ incorrectly use dynamic TLS, and depending on how the
+ free function was compiled, it could call
+ __tls_get_addr before the null pointer check in the
+ free implementation. Checking here papers over at
+ least some dynamic TLS usage by interposed mallocs. */
+ if (dtv[modid].pointer.to_free != NULL)
+ free (dtv[modid].pointer.to_free);
dtv[modid].pointer.val = TLS_DTV_UNALLOCATED;
dtv[modid].pointer.to_free = NULL;