mirror of git://sourceware.org/git/glibc.git
83 lines
3.6 KiB
C
83 lines
3.6 KiB
C
/* Common declarations for the setenv/getenv family of functions.
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Copyright (C) 2024-2025 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 _SETENV_H
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#define _SETENV_H
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#include <atomic.h>
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#include <stdbool.h>
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/* We use an exponential sizing policy for environment arrays. The
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arrays are not deallocating during the lifetime of the process.
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This adds between one and two additional pointers per active
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environemnt entry, on top of what is used by setenv to keep track
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of environment values used before. */
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struct environ_array
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{
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/* The actual environment array. Use a separate allocation (and not
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a flexible array member) so that calls like free (environ) that
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have been encountered in some applications do not crash
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immediately. With such a call, if the application restores the
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original environ pointer at process start and does not modify the
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environment again, a use-after-free situation only occurs during
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__libc_freeres, which is only called during memory debugging.
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With subsequent setenv calls, there is still heap corruption, but
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that happened with the old realloc-based implementation, too. */
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char **array;
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size_t allocated; /* Number of allocated array elments. */
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struct environ_array *next; /* Previously used environment array. */
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};
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/* After initialization, and until the user resets environ (perhaps by
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calling clearenv), &__environ[0] == &environ_array_list->array[0]. */
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extern struct environ_array *__environ_array_list attribute_hidden;
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/* Returns true if EP (which should be an __environ value) is a
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pointer managed by setenv. */
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static inline bool
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__environ_is_from_array_list (char **ep)
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{
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struct environ_array *eal = atomic_load_relaxed (&__environ_array_list);
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return eal != NULL && eal->array == ep;
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}
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/* Counter for detecting concurrent modification in unsetenv.
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Ideally, this should be a 64-bit counter that cannot wrap around,
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but given that counter wrapround is probably impossible to hit
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(2**32 operations in unsetenv concurrently with getenv), using
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<atomic_wide_counter.h> seems unnecessary. */
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#if __HAVE_64B_ATOMICS
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typedef uint64_t environ_counter;
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#else
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typedef uint32_t environ_counter;
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#endif
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/* Updated by unsetenv to detect multiple overwrites in getenv. */
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extern environ_counter __environ_counter attribute_hidden;
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/* This function is used by `setenv' and `putenv'. The difference between
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the two functions is that for the former must create a new string which
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is then placed in the environment, while the argument of `putenv'
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must be used directly. This is all complicated by the fact that we try
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to reuse values once generated for a `setenv' call since we can never
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free the strings. */
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int __add_to_environ (const char *name, const char *value,
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const char *combines, int replace) attribute_hidden;
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#endif /* _SETENV_H */
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