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73 lines
2.9 KiB
C
73 lines
2.9 KiB
C
/* Threshold at which to diagnose ELOOP. Generic version.
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Copyright (C) 2012-2020 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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#ifndef _ELOOP_THRESHOLD_H
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#define _ELOOP_THRESHOLD_H 1
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#include <limits.h>
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#include <sys/param.h>
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/* POSIX specifies SYMLOOP_MAX as the "Maximum number of symbolic
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links that can be reliably traversed in the resolution of a
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pathname in the absence of a loop." This makes it a minimum that
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we should certainly accept. But it leaves open the possibility
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that more might sometimes work--just not "reliably".
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For example, Linux implements a complex policy whereby there is a
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small limit on the number of direct symlink traversals (a symlink
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to a symlink to a symlink), but larger limit on the total number of
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symlink traversals overall. Hence the SYMLOOP_MAX number should be
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the small one, but the limit library functions enforce on users
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should be the larger one.
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So, we use the larger of the reported SYMLOOP_MAX (if any) and our
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own constant MIN_ELOOP_THRESHOLD, below. This constant should be
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large enough that it never rules out a file name and directory tree
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that the underlying system (i.e. calls to 'open' et al) would
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resolve successfully. It should be small enough that actual loops
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are detected without a huge number of iterations. */
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#ifndef MIN_ELOOP_THRESHOLD
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# define MIN_ELOOP_THRESHOLD 40
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#endif
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/* Return the maximum number of symlink traversals to permit
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before diagnosing ELOOP. */
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static inline unsigned int __attribute__ ((const))
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__eloop_threshold (void)
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{
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#ifdef SYMLOOP_MAX
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const int symloop_max = SYMLOOP_MAX;
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#else
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/* The function is marked 'const' even though we use memory and
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call a function, because sysconf is required to return the
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same value in every call and so it must always be safe to
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call __eloop_threshold exactly once and reuse the value. */
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static long int sysconf_symloop_max;
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if (sysconf_symloop_max == 0)
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sysconf_symloop_max = __sysconf (_SC_SYMLOOP_MAX);
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const unsigned int symloop_max = (sysconf_symloop_max <= 0
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? _POSIX_SYMLOOP_MAX
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: sysconf_symloop_max);
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#endif
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return MAX (symloop_max, MIN_ELOOP_THRESHOLD);
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}
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#endif /* eloop-threshold.h */
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