Bug 20116: Fix use after free in pthread_create()

The commit documents the ownership rules around 'struct pthread' and
when a thread can read or write to the descriptor. With those ownership
rules in place it becomes obvious that pd->stopped_start should not be
touched in several of the paths during thread startup, particularly so
for detached threads. In the case of detached threads, between the time
the thread is created by the OS kernel and the creating thread checks
pd->stopped_start, the detached thread might have already exited and the
memory for pd unmapped. As a regression test we add a simple test which
exercises this exact case by quickly creating detached threads with
large enough stacks to ensure the thread stack cache is bypassed and the
stacks are unmapped. Before the fix the testcase segfaults, after the
fix it works correctly and completes without issue.

For a detailed discussion see:
https://www.sourceware.org/ml/libc-alpha/2017-01/msg00505.html

(cherry picked from commit f8bf15febcaf137bbec5a61101e88cd5a9d56ca8)

1 files changed, 2 insertions, 1 deletions

diff --git a/nptl/Makefile b/nptl/Makefile
index 1aa52afd71..6928477501 100644
--- a/nptl/Makefile
+++ b/nptl/Makefile
@@ -291,7 +291,8 @@ tests = tst-typesizes \
 			    c89 gnu89 c99 gnu99 c11 gnu11) \
 	tst-bad-schedattr \
 	tst-thread_local1 tst-mutex-errorcheck tst-robust10 \
-	tst-minstack-cancel tst-minstack-exit
+	tst-minstack-cancel tst-minstack-exit \
+	tst-create-detached
 
 xtests = tst-setuid1 tst-setuid1-static tst-setuid2 \
 	tst-mutexpp1 tst-mutexpp6 tst-mutexpp10