From b9f72bd5de931eac39219018c2fa319a449bb2cf Mon Sep 17 00:00:00 2001 From: Siddhesh Poyarekar Date: Tue, 13 Aug 2024 21:08:49 -0400 Subject: 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 Reviewed-by: Carlos O'Donell (cherry picked from commit 3e1d8d1d1dca24ae90df2ea826a8916896fc7e77) --- libio/genops.c | 6 ++++++ libio/libioP.h | 4 ++-- stdio-common/Makefile | 7 +++++++ stdio-common/tst-ungetc-leak.c | 32 ++++++++++++++++++++++++++++++++ 4 files changed, 47 insertions(+), 2 deletions(-) create mode 100644 stdio-common/tst-ungetc-leak.c diff --git a/libio/genops.c b/libio/genops.c index c673c0a..fb06245 100644 --- a/libio/genops.c +++ b/libio/genops.c @@ -789,6 +789,12 @@ _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 745278e..e75ee77 100644 --- a/libio/libioP.h +++ b/libio/libioP.h @@ -577,8 +577,8 @@ 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 2bcbaf7..3810405 100644 --- a/stdio-common/Makefile +++ b/stdio-common/Makefile @@ -256,6 +256,7 @@ tests := \ tst-swscanf \ tst-tmpnam \ tst-ungetc \ + tst-ungetc-leak \ tst-unlockedio \ tst-vfprintf-mbs-prec \ tst-vfprintf-user-type \ @@ -300,6 +301,7 @@ tests-special += \ $(objpfx)tst-printfsz-islongdouble.out \ $(objpfx)tst-setvbuf1-cmp.out \ $(objpfx)tst-unbputc.out \ + $(objpfx)tst-ungetc-leak-mem.out \ $(objpfx)tst-vfprintf-width-prec-mem.out \ # tests-special @@ -314,6 +316,8 @@ generated += \ tst-printf-fp-leak-mem.out \ tst-printf-fp-leak.mtrace \ tst-scanf-bz27650.mtrace \ + tst-ungetc-leak-mem.out \ + tst-ungetc-leak.mtrace \ tst-vfprintf-width-prec-mem.out \ tst-vfprintf-width-prec.mtrace \ # generated @@ -403,6 +407,9 @@ tst-printf-fp-leak-ENV = \ tst-scanf-bz27650-ENV = \ MALLOC_TRACE=$(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 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 + . */ + +#include +#include +#include +#include + +static int +do_test (void) +{ + mtrace (); + TEST_COMPARE (ungetc('y', stdin), 'y'); + return 0; +} + +#include -- cgit v1.1