From: Rich Felker <dalias@aerifal.cx>
Date: Sat, 19 Feb 2011 16:04:36 +0000 (-0500)
Subject: race condition fix: block all signals before decrementing thread count
X-Git-Url: http://nsz.repo.hu/git/?p=musl;a=commitdiff_plain;h=19eb13b9a4cf2f787f60b6e2a6d26a6cd7d3ffd2

race condition fix: block all signals before decrementing thread count

the existence of a (kernelspace) thread must never have observable
effects after the thread count is decremented. if signals are not
blocked, it could end up handling the signal for rsyscall and
contributing towards the count of threads which have changed ids,
causing a thread to be missed. this could lead to one thread retaining
unwanted privilege level.

this change may also address other subtle race conditions in
application code that uses signals.
---

diff --git a/src/thread/i386/__unmapself.s b/src/thread/i386/__unmapself.s
index 5c674966..bcf6e7fe 100644
--- a/src/thread/i386/__unmapself.s
+++ b/src/thread/i386/__unmapself.s
@@ -2,15 +2,6 @@
 .global __unmapself
 .type   __unmapself,%function
 __unmapself:
-	call 1f
-	.long -1
-	.long -1
-1:	popl %ecx
-	xorl %ebx,%ebx
-	xorl %edx,%edx
-	movl $8,%esi
-	movl $175,%eax
-	int $128
 	movl $91,%eax
 	movl 4(%esp),%ebx
 	movl 8(%esp),%ecx
diff --git a/src/thread/pthread_create.c b/src/thread/pthread_create.c
index 7c436957..c73c5211 100644
--- a/src/thread/pthread_create.c
+++ b/src/thread/pthread_create.c
@@ -25,6 +25,8 @@ void __pthread_unwind_next(struct __ptcb *cb)
 		}
 	}
 
+	syscall4(__NR_sigprocmask, SIG_BLOCK, (long)(uint64_t[1]){-1}, 0, 8);
+
 	if (!a_fetch_add(&libc.threads_minus_1, -1))
 		exit(0);
 
diff --git a/src/thread/x86_64/__unmapself.s b/src/thread/x86_64/__unmapself.s
index 59092eaa..d36257d0 100644
--- a/src/thread/x86_64/__unmapself.s
+++ b/src/thread/x86_64/__unmapself.s
@@ -3,19 +3,6 @@
 .global __unmapself
 .type   __unmapself,%function
 __unmapself:
-	call 1f         /* glibc ABI compat */
-	.long -1
-	.long -1
-1:      push %rsi       /* save arg2 for munmap */
-	push %rdx       /* save arg3 for munmap */
-	mov %rdi,%rsi   /* rt_sigprocmask() args: move arg1 to rsi */
-	xor %rdi,%rdi
-	xor %rdx,%rdx
-	movq $8,%r10
-	movl $14,%eax   /* __NR_rt_sigprocmask */
-	syscall         /* call rt_sigprocmask(0,arg1,0,8) */
-	pop %rsi        /* munmap() args: reload from stack */
-	pop %rdi
 	movl $11,%eax   /* __NR_munmap */
 	syscall         /* munmap(arg2,arg3) */
 	xor %rdi,%rdi   /* exit() args: always return success */