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ed6a68bac7
The 7bb8045ec0 path made the '%n' fortify check ignore EMFILE errors while trying to open /proc/self/maps, and this added a security issue where EMFILE can be attacker-controlled thus making it ineffective for some cases. The EMFILE failure is reinstated but with a different error message. Also, to improve the false positive of the hardening for the cases where no new files can be opened, the _dl_readonly_area now uses _dl_find_object to check if the memory area is within a writable ELF segment. The procfs method is still used as fallback. Checked on x86_64-linux-gnu and i686-linux-gnu. Reviewed-by: Arjun Shankar <arjun@redhat.com>
87 lines
2.8 KiB
C
87 lines
2.8 KiB
C
/* Check if range is within a read-only from a loaded ELF object.
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Copyright (C) 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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#include <ldsodefs.h>
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static bool
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check_relro (const struct link_map *l, uintptr_t start, uintptr_t end)
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{
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if (l->l_relro_addr != 0)
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{
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uintptr_t relro_start = ALIGN_DOWN (l->l_addr + l->l_relro_addr,
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GLRO(dl_pagesize));
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uintptr_t relro_end = ALIGN_DOWN (l->l_addr + l->l_relro_addr
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+ l->l_relro_size,
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GLRO(dl_pagesize));
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/* RELRO is caved out from a RW segment, so the next range is either
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RW or nonexistent. */
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return relro_start <= start && end <= relro_end
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? dl_readonly_area_rdonly : dl_readonly_area_writable;
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}
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return dl_readonly_area_writable;
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}
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enum dl_readonly_area_error_type
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_dl_readonly_area (const void *ptr, size_t size)
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{
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struct dl_find_object dlfo;
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if (_dl_find_object ((void *)ptr, &dlfo) != 0)
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return dl_readonly_area_not_found;
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const struct link_map *l = dlfo.dlfo_link_map;
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uintptr_t ptr_start = (uintptr_t) ptr;
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uintptr_t ptr_end = ptr_start + size;
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for (const ElfW(Phdr) *ph = l->l_phdr; ph < &l->l_phdr[l->l_phnum]; ++ph)
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if (ph->p_type == PT_LOAD)
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{
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/* For segments with alignment larger than the page size,
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_dl_map_segment allocates additional space that is mark as
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PROT_NONE (so we can ignore). */
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uintptr_t from = l->l_addr
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+ ALIGN_DOWN (ph->p_vaddr, GLRO(dl_pagesize));
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uintptr_t to = l->l_addr
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+ ALIGN_UP (ph->p_vaddr + ph->p_filesz, GLRO(dl_pagesize));
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/* Found an entry that at least partially covers the area. */
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if (from < ptr_end && to > ptr_start)
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{
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if (ph->p_flags & PF_W)
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return check_relro (l, ptr_start, ptr_end);
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if ((ph->p_flags & PF_R) == 0)
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return dl_readonly_area_writable;
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if (from <= ptr_start && to >= ptr_end)
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return dl_readonly_area_rdonly;
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else if (from <= ptr_start)
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size -= to - ptr_start;
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else if (to >= ptr_end)
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size -= ptr_end - from;
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else
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size -= to - from;
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if (size == 0)
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break;
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}
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}
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return size == 0 ? dl_readonly_area_rdonly : dl_readonly_area_not_found;
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}
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