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commit 40ebfd016ad284872f434bdd76dbe9c708db4d6b
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Author: Florian Weimer <fweimer@redhat.com>
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Date: Fri Jun 25 08:09:08 2021 +0200
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elf: Disable most of TLS modid gaps processing [BZ #27135]
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Revert "elf: Fix DTV gap reuse logic [BZ #27135]"
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This reverts commit 572bd547d57a39b6cf0ea072545dc4048921f4c3.
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It turns out that the _dl_next_tls_modid in _dl_map_object_from_fd keeps
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returning the same modid over and over again if there is a gap and
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more than TLS-using module is loaded in one dlopen call. This corrupts
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TLS data structures. The bug is still present after a revert, but
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empirically it is much more difficult to trigger (because it involves a
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dlopen failure).
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diff --git a/elf/dl-close.c b/elf/dl-close.c
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index 41cb6c58491c364b..7d2dc2272cd643f5 100644
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--- a/elf/dl-close.c
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+++ b/elf/dl-close.c
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@@ -88,11 +88,7 @@ remove_slotinfo (size_t idx, struct dtv_slotinfo_list *listp, size_t disp,
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/* If this is not the last currently used entry no need to look
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further. */
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if (idx != GL(dl_tls_max_dtv_idx))
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- {
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- /* There is an unused dtv entry in the middle. */
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- GL(dl_tls_dtv_gaps) = true;
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- return true;
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- }
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+ return true;
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}
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while (idx - disp > (disp == 0 ? 1 + GL(dl_tls_static_nelem) : 0))
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diff --git a/elf/dl-open.c b/elf/dl-open.c
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index 54727402750f4c0c..a67fb3aee40860e1 100644
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--- a/elf/dl-open.c
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+++ b/elf/dl-open.c
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@@ -896,6 +896,16 @@ no more namespaces available for dlmopen()"));
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state if relocation failed, for example. */
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if (args.map)
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{
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+ /* Maybe some of the modules which were loaded use TLS.
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+ Since it will be removed in the following _dl_close call
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+ we have to mark the dtv array as having gaps to fill the
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+ holes. This is a pessimistic assumption which won't hurt
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+ if not true. There is no need to do this when we are
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+ loading the auditing DSOs since TLS has not yet been set
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+ up. */
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+ if ((mode & __RTLD_AUDIT) == 0)
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+ GL(dl_tls_dtv_gaps) = true;
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+
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_dl_close_worker (args.map, true);
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/* All l_nodelete_pending objects should have been deleted
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diff --git a/elf/dl-tls.c b/elf/dl-tls.c
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index bacb4101e2e2c4e5..801eafad3961573c 100644
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--- a/elf/dl-tls.c
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+++ b/elf/dl-tls.c
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@@ -187,7 +187,10 @@ _dl_next_tls_modid (void)
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size_t
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_dl_count_modids (void)
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{
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- /* The count is the max unless dlclose or failed dlopen created gaps. */
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+ /* It is rare that we have gaps; see elf/dl-open.c (_dl_open) where
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+ we fail to load a module and unload it leaving a gap. If we don't
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+ have gaps then the number of modids is the current maximum so
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+ return that. */
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if (__glibc_likely (!GL(dl_tls_dtv_gaps)))
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return GL(dl_tls_max_dtv_idx);
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