correct locking in stdio functions that tried to be lock-free

[musl] / src / stdio / freopen.c

diff --git a/src/stdio/freopen.c b/src/stdio/freopen.c
index c80ce3b..7ae116d 100644 (file)
--- a/src/stdio/freopen.c
+++ b/src/stdio/freopen.c
@@ -4,8 +4,9 @@
  * hack the necessary parts of the new FILE into the old one, then
  * close the 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);
 
 
 int __dup3(int, int, int);
 


@@ -14,6 +15,8 @@ FILE *freopen(const char *restrict filename, const char *restrict mode, FILE *re
        int fl = __fmodeflags(mode);
        FILE *f2;
 
        int fl = __fmodeflags(mode);
        FILE *f2;
 

+       FLOCK(f);
+

        fflush(f);
 
        if (!filename) {
        fflush(f);
 
        if (!filename) {


@@ -22,21 +25,22 @@ 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;
                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;
        } 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:
        return f;
 
 fail2: