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io: nftw/ftw: Fix stack overflow with large nopenfd [BZ #26353]
The nopenfd value is used as argument for the internal buffer on ftw_statup, which is allocated with alloca and might trigger a stack overflow for large values. This patch replaces the memory allocation to use malloc instead. Checked on x86_64-linux-gnu. Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
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@ -68,7 +68,8 @@ tests := test-utime test-stat test-stat2 test-lfs tst-getcwd \
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tst-posix_fallocate tst-posix_fallocate64 \
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tst-fts tst-fts-lfs tst-open-tmpfile \
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tst-copy_file_range tst-getcwd-abspath tst-lockf \
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tst-ftw-lnk tst-file_change_detection tst-lchmod
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tst-ftw-lnk tst-file_change_detection tst-lchmod \
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tst-ftw-bz26353
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# Likewise for statx, but we do not need static linking here.
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tests-internal += tst-statx
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16
io/ftw.c
16
io/ftw.c
@ -646,15 +646,17 @@ ftw_startup (const char *dir, int is_nftw, void *func, int descriptors,
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data.maxdir = descriptors < 1 ? 1 : descriptors;
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data.actdir = 0;
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data.dirstreams = (struct dir_data **) alloca (data.maxdir
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* sizeof (struct dir_data *));
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memset (data.dirstreams, '\0', data.maxdir * sizeof (struct dir_data *));
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/* PATH_MAX is always defined when we get here. */
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data.dirbufsize = MAX (2 * strlen (dir), PATH_MAX);
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data.dirbuf = (char *) malloc (data.dirbufsize);
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if (data.dirbuf == NULL)
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data.dirstreams = malloc (data.maxdir * sizeof (struct dir_data *)
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+ data.dirbufsize);
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if (data.dirstreams == NULL)
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return -1;
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memset (data.dirstreams, '\0', data.maxdir * sizeof (struct dir_data *));
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data.dirbuf = (char *) data.dirstreams
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+ data.maxdir * sizeof (struct dir_data *);
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cp = __stpcpy (data.dirbuf, dir);
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/* Strip trailing slashes. */
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while (cp > data.dirbuf + 1 && cp[-1] == '/')
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@ -803,7 +805,7 @@ ftw_startup (const char *dir, int is_nftw, void *func, int descriptors,
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out_fail:
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save_err = errno;
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__tdestroy (data.known_objects, free);
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free (data.dirbuf);
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free (data.dirstreams);
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__set_errno (save_err);
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return result;
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70
io/tst-ftw-bz26353.c
Normal file
70
io/tst-ftw-bz26353.c
Normal file
@ -0,0 +1,70 @@
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/* test ftw bz26353: Check whether stack overflow occurs when the value
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of the nopenfd parameter is too large.
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Copyright (C) 2020 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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#include <stdlib.h>
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#include <stdio.h>
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#include <ftw.h>
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#include <errno.h>
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#include <sys/resource.h>
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#include <support/temp_file.h>
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#include <support/capture_subprocess.h>
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#include <support/check.h>
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static int
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my_func (const char *file, const struct stat *sb, int flag)
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{
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return 0;
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}
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static int
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get_large_nopenfd (void)
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{
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struct rlimit r;
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TEST_COMPARE (getrlimit (RLIMIT_STACK, &r), 0);
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if (r.rlim_cur == RLIM_INFINITY)
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{
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r.rlim_cur = 8 * 1024 * 1024;
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TEST_COMPARE (setrlimit (RLIMIT_STACK, &r), 0);
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}
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return (int) r.rlim_cur;
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}
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static void
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do_ftw (void *unused)
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{
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char *tempdir = support_create_temp_directory ("tst-bz26353");
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int large_nopenfd = get_large_nopenfd ();
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TEST_COMPARE (ftw (tempdir, my_func, large_nopenfd), 0);
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free (tempdir);
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}
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/* Check whether stack overflow occurs. */
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static int
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do_test (void)
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{
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struct support_capture_subprocess result;
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result = support_capture_subprocess (do_ftw, NULL);
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support_capture_subprocess_check (&result, "bz26353", 0, sc_allow_none);
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support_capture_subprocess_free (&result);
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return 0;
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}
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#include <support/test-driver.c>
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