X-Git-Url: http://nsz.repo.hu/git/?p=musl;a=blobdiff_plain;f=src%2Fstdio%2Ffreopen.c;h=6c1b575f527963566a7b457f29c18dea45b2505a;hp=c80ce3b438e67e7de275cd2ef1a3a0513d5e05cd;hb=b5a527f9ff47b0f4b32c606e385a0c27d861a475;hpb=892cafff665b44d238e3b664f61ca38dd965cba6

diff --git a/src/stdio/freopen.c b/src/stdio/freopen.c
index c80ce3b4..6c1b575f 100644
--- a/src/stdio/freopen.c
+++ b/src/stdio/freopen.c
@@ -1,11 +1,13 @@
 #include "stdio_impl.h"
+#include <fcntl.h>
 
 /* The basic idea of this implementation is to open a new FILE,
  * hack the necessary parts of the new FILE into the old one, then
  * close the new FILE. */
 
-/* Locking is not necessary because, in the event of failure, the stream
- * passed to freopen is invalid as soon as freopen is called. */
+/* Locking IS necessary because another thread may provably hold the
+ * lock, via flockfile or otherwise, when freopen is called, and in that
+ * case, freopen cannot act until the lock is released. */
 
 int __dup3(int, int, int);
 
@@ -14,6 +16,8 @@ FILE *freopen(const char *restrict filename, const char *restrict mode, FILE *re
 	int fl = __fmodeflags(mode);
 	FILE *f2;
 
+	FLOCK(f);
+
 	fflush(f);
 
 	if (!filename) {
@@ -22,21 +26,22 @@ FILE *freopen(const char *restrict filename, const char *restrict mode, FILE *re
 		fl &= ~(O_CREAT|O_EXCL|O_CLOEXEC);
 		if (syscall(SYS_fcntl, f->fd, F_SETFL, fl) < 0)
 			goto fail;
-		return f;
 	} else {
 		f2 = fopen(filename, mode);
 		if (!f2) goto fail;
 		if (f2->fd == f->fd) f2->fd = -1; /* avoid closing in fclose */
 		else if (__dup3(f2->fd, f->fd, fl&O_CLOEXEC)<0) goto fail2;
-	}
 
-	f->flags = (f->flags & F_PERM) | f2->flags;
-	f->read = f2->read;
-	f->write = f2->write;
-	f->seek = f2->seek;
-	f->close = f2->close;
+		f->flags = (f->flags & F_PERM) | f2->flags;
+		f->read = f2->read;
+		f->write = f2->write;
+		f->seek = f2->seek;
+		f->close = f2->close;
 
-	fclose(f2);
+		fclose(f2);
+	}
+
+	FUNLOCK(f);
 	return f;
 
 fail2: