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authorRich Felker <dalias@aerifal.cx>2011-06-14 01:35:51 -0400
committerRich Felker <dalias@aerifal.cx>2011-06-14 01:35:51 -0400
commit7779dbd2663269b465951189b4f43e70839bc073 (patch)
treefa131e2ddcf164bf4d58a07f627a4704a0b13f73 /src/thread
parentf58c8a0f391987a65e055ae591ec59b9df7b7f7c (diff)
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fix race condition in pthread_kill
if thread id was reused by the kernel between the time pthread_kill read it from the userspace pthread_t object and the time of the tgkill syscall, a signal could be sent to the wrong thread. the tgkill syscall was supposed to prevent this race (versus the old tkill syscall) but it can't; it can only help in the case where the tid is reused in a different process, but not when the tid is reused in the same process. the only solution i can see is an extra lock to prevent threads from exiting while another thread is trying to pthread_kill them. it should be very very cheap in the non-contended case.
Diffstat (limited to 'src/thread')
-rw-r--r--src/thread/pthread_create.c2
-rw-r--r--src/thread/pthread_kill.c6
2 files changed, 7 insertions, 1 deletions
diff --git a/src/thread/pthread_create.c b/src/thread/pthread_create.c
index c856c581..d60c2a4d 100644
--- a/src/thread/pthread_create.c
+++ b/src/thread/pthread_create.c
@@ -27,7 +27,9 @@ void __pthread_unwind_next(struct __ptcb *cb)
__lock(&self->exitlock);
/* Mark this thread dead before decrementing count */
+ __lock(&self->killlock);
self->dead = 1;
+ a_store(&self->killlock, 0);
do n = libc.threads_minus_1;
while (n && a_cas(&libc.threads_minus_1, n, n-1)!=n);
diff --git a/src/thread/pthread_kill.c b/src/thread/pthread_kill.c
index 36e9b6da..a24ecc20 100644
--- a/src/thread/pthread_kill.c
+++ b/src/thread/pthread_kill.c
@@ -2,5 +2,9 @@
int pthread_kill(pthread_t t, int sig)
{
- return -__syscall(SYS_tgkill, t->pid, t->tid, sig);
+ int r;
+ __lock(&t->killlock);
+ r = t->dead ? ESRCH : -__syscall(SYS_tgkill, t->pid, t->tid, sig);
+ a_store(&t->killlock, 0);
+ return r;
}