ungetc: Fix backup buffer leak on program exit [BZ #27821]

If a file descriptor is left unclosed and is cleaned up by _IO_cleanup
on exit, its backup buffer remains unfreed, registering as a leak in
valgrind.  This is not strictly an issue since (1) the program should
ideally be closing the stream once it's not in use and (2) the program
is about to exit anyway, so keeping the backup buffer around a wee bit
longer isn't a real problem.  Free it anyway to keep valgrind happy
when the streams in question are the standard ones, i.e. stdout, stdin
or stderr.

Also, the _IO_have_backup macro checks for _IO_save_base,
which is a roundabout way to check for a backup buffer instead of
directly looking for _IO_backup_base.  The roundabout check breaks when
the main get area has not been used and user pushes a char into the
backup buffer with ungetc.  Fix this to use the _IO_backup_base
directly.

Signed-off-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
Reviewed-by: Carlos O'Donell <carlos@redhat.com>
(cherry picked from commit 3e1d8d1d1dca24ae90df2ea826a8916896fc7e77)
(cherry picked from commit b9f72bd5de931eac39219018c2fa319a449bb2cf)

diff --git a/libio/genops.c b/libio/genops.c
index a5dd6a06d9e259d8e30a3537b7741e45cdf3d9e9..b5fc53fd1ef6e91173bec118aa367aaf6bd36780 100644 (file)
--- a/libio/genops.c
+++ b/libio/genops.c
@@ -796,6 +796,12 @@ _IO_unbuffer_all (void)
        legacy = 1;
 #endif
 
+      /* Free up the backup area if it was ever allocated.  */
+      if (_IO_have_backup (fp))
+       _IO_free_backup_area (fp);
+      if (fp->_mode > 0 && _IO_have_wbackup (fp))
+       _IO_free_wbackup_area (fp);
+
       if (! (fp->_flags & _IO_UNBUFFERED)
          /* Iff stream is un-orientated, it wasn't used. */
          && (legacy || fp->_mode != 0))

diff --git a/libio/libioP.h b/libio/libioP.h
index dc9a2ce9c8d7744c1a857a2d69173d66ca484a30..bab5f3770f0760c48fa956a9a35a5be6e0a2dc0f 100644 (file)
--- a/libio/libioP.h
+++ b/libio/libioP.h
@@ -529,8 +529,8 @@ extern void _IO_old_init (FILE *fp, int flags) __THROW;
        ((__fp)->_wide_data->_IO_write_base \
        = (__fp)->_wide_data->_IO_write_ptr = __p, \
        (__fp)->_wide_data->_IO_write_end = (__ep))
-#define _IO_have_backup(fp) ((fp)->_IO_save_base != NULL)
-#define _IO_have_wbackup(fp) ((fp)->_wide_data->_IO_save_base != NULL)
+#define _IO_have_backup(fp) ((fp)->_IO_backup_base != NULL)
+#define _IO_have_wbackup(fp) ((fp)->_wide_data->_IO_backup_base != NULL)
 #define _IO_in_backup(fp) ((fp)->_flags & _IO_IN_BACKUP)
 #define _IO_have_markers(fp) ((fp)->_markers != NULL)
 #define _IO_blen(fp) ((fp)->_IO_buf_end - (fp)->_IO_buf_base)

diff --git a/stdio-common/Makefile b/stdio-common/Makefile
index 08bedd01be61a55d94fc0a27b9c800f0e931063e..f10bf28878e0aebc032e8c6e749c3a4f09b131c1 100644 (file)
--- a/stdio-common/Makefile
+++ b/stdio-common/Makefile
@@ -201,6 +201,7 @@ tests := \
   tst-swscanf \
   tst-tmpnam \
   tst-ungetc \
+  tst-ungetc-leak \
   tst-unlockedio \
   tst-vfprintf-mbs-prec \
   tst-vfprintf-user-type \
@@ -229,6 +230,7 @@ tests-special += \
   $(objpfx)tst-printfsz-islongdouble.out \
   $(objpfx)tst-setvbuf1-cmp.out \
   $(objpfx)tst-unbputc.out \
+  $(objpfx)tst-ungetc-leak-mem.out \
   $(objpfx)tst-vfprintf-width-prec-mem.out \
   # tests-special
 
@@ -243,6 +245,8 @@ generated += \
   tst-printf-fp-leak-mem.out \
   tst-printf-fp-leak.mtrace \
   tst-scanf-bz27650.mtrace \
+  tst-ungetc-leak-mem.out \
+  tst-ungetc-leak.mtrace \
   tst-vfprintf-width-prec-mem.out \
   tst-vfprintf-width-prec.mtrace \
   # generated
@@ -288,6 +292,9 @@ tst-printf-fp-leak-ENV = \
 tst-scanf-bz27650-ENV = \
   MALLOC_TRACE=$(objpfx)tst-scanf-bz27650.mtrace \
   LD_PRELOAD=$(common-objpfx)malloc/libc_malloc_debug.so
+tst-ungetc-leak-ENV = \
+  MALLOC_TRACE=$(objpfx)tst-ungetc-leak.mtrace \
+  LD_PRELOAD=$(common-objpfx)malloc/libc_malloc_debug.so
 
 $(objpfx)tst-unbputc.out: tst-unbputc.sh $(objpfx)tst-unbputc
        $(SHELL) $< $(common-objpfx) '$(test-program-prefix)'; \

diff --git a/stdio-common/tst-ungetc-leak.c b/stdio-common/tst-ungetc-leak.c
new file mode 100644 (file)
index 0000000..6c5152b
--- /dev/null
+++ b/stdio-common/tst-ungetc-leak.c
@@ -0,0 +1,32 @@
+/* Test for memory leak with ungetc when stream is unused.
+   Copyright The GNU Toolchain Authors.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <stdio.h>
+#include <mcheck.h>
+#include <support/check.h>
+#include <support/support.h>
+
+static int
+do_test (void)
+{
+  mtrace ();
+  TEST_COMPARE (ungetc('y', stdin), 'y');
+  return 0;
+}
+
+#include <support/test-driver.c>