[glibc] hurd: writev: Add back cleanup handler

[Samuel Thibault <sthibaul@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=c6957bddb939a1a602824b9fa731fc45fb4a6d8c

commit c6957bddb939a1a602824b9fa731fc45fb4a6d8c
Author: Joe Simmons-Talbott <josimmon@redhat.com>
Date:   Mon Jun 19 10:38:42 2023 -0400

    hurd: writev: Add back cleanup handler
    
    There is a potential memory leak for large writes due to writev being a
    "shall occur" cancellation point.  Add back the cleanup handler removed
    in cf30aa43a5917f441c9438aaee201c53c8e1d76b.
    
    Checked on i686-gnu and x86_64-linux-gnu.
    Message-Id: <20230619143842.2901522-1-josimmon@redhat.com>

Diff:
---
 sysdeps/posix/writev.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/sysdeps/posix/writev.c b/sysdeps/posix/writev.c
index d4c3cf6f03..0c86e7ea5e 100644
--- a/sysdeps/posix/writev.c
+++ b/sysdeps/posix/writev.c
@@ -26,6 +26,12 @@
 #include <errno.h>
 
 
+static void
+ifree (struct scratch_buffer *sbuf)
+{
+   scratch_buffer_free (sbuf);
+}
+
 /* Write data pointed by the buffers described by VECTOR, which
    is a vector of COUNT 'struct iovec's, to file descriptor FD.
    The data is written in the order specified.
@@ -51,7 +57,7 @@ __writev (int fd, const struct iovec *vector, int count)
      since it's faster for small buffer sizes but can handle larger
      allocations as well.  */
 
-  struct scratch_buffer buf;
+  struct scratch_buffer __attribute__ ((__cleanup__ (ifree))) buf;
   scratch_buffer_init (&buf);
   if (!scratch_buffer_set_array_size (&buf, 1, bytes))
     /* XXX I don't know whether it is acceptable to try writing
@@ -75,8 +81,6 @@ __writev (int fd, const struct iovec *vector, int count)
 
   ssize_t bytes_written = __write (fd, buffer, bytes);
 
-  scratch_buffer_free (&buf);
-
   return bytes_written;
 }
 libc_hidden_def (__writev)