From c0669ae1a629e16b536bf11cdd0865e0dbcf4bee Mon Sep 17 00:00:00 2001 From: Szabolcs Nagy Date: Wed, 30 Dec 2020 21:52:38 +0000 Subject: [PATCH] elf: Refactor _dl_update_slotinfo to avoid use after free map is not valid to access here because it can be freed by a concurrent dlclose: during tls access (via __tls_get_addr) _dl_update_slotinfo is called without holding dlopen locks. So don't check the modid of map. The map == 0 and map != 0 code paths can be shared (avoiding the dtv resize in case of map == 0 is just an optimization: larger dtv than necessary would be fine too). Reviewed-by: Adhemerval Zanella --- elf/dl-tls.c | 21 +++++---------------- 1 file changed, 5 insertions(+), 16 deletions(-) --- Upstream-Status: Backport [https://sourceware.org/git/?p=glibc.git;a=patch;h=c0669ae1a629e16b536bf11cdd0865e0dbcf4bee] Signed-off-by: Akash Hadke Signed-off-by: Akash Hadke --- diff --git a/elf/dl-tls.c b/elf/dl-tls.c index 24d00c14ef..f8b32b3ecb 100644 --- a/elf/dl-tls.c +++ b/elf/dl-tls.c @@ -743,6 +743,8 @@ _dl_update_slotinfo (unsigned long int req_modid) { for (size_t cnt = total == 0 ? 1 : 0; cnt < listp->len; ++cnt) { + size_t modid = total + cnt; + size_t gen = listp->slotinfo[cnt].gen; if (gen > new_gen) @@ -758,25 +760,12 @@ _dl_update_slotinfo (unsigned long int req_modid) /* If there is no map this means the entry is empty. */ struct link_map *map = listp->slotinfo[cnt].map; - if (map == NULL) - { - if (dtv[-1].counter >= total + cnt) - { - /* If this modid was used at some point the memory - might still be allocated. */ - free (dtv[total + cnt].pointer.to_free); - dtv[total + cnt].pointer.val = TLS_DTV_UNALLOCATED; - dtv[total + cnt].pointer.to_free = NULL; - } - - continue; - } - /* Check whether the current dtv array is large enough. */ - size_t modid = map->l_tls_modid; - assert (total + cnt == modid); if (dtv[-1].counter < modid) { + if (map == NULL) + continue; + /* Resize the dtv. */ dtv = _dl_resize_dtv (dtv); -- 2.27.0