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elf: Canonicalize $ORIGIN in an explicit ld.so invocation [BZ 25263]

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When an executable is invoked directly, we calculate $ORIGIN by calling
readlink on /proc/self/exe, which the Linux kernel resolves to the
target of any symlinks.  However, if an executable is run through ld.so,
we cannot use /proc/self/exe and instead use the path given as an
argument.  This leads to a different calculation of $ORIGIN, which is
most notable in that it causes ldd to behave differently (e.g., by not
finding a library) from directly running the program.

To make the behavior consistent, take advantage of the fact that the
kernel also resolves /proc/self/fd/ symlinks to the target of any
symlinks in the same manner, so once we have opened the main executable
in order to load it, replace the user-provided path with the result of
calling readlink("/proc/self/fd/N").

(On non-Linux platforms this resolution does not happen and so no
behavior change is needed.)

The __fd_to_filename requires _fitoa_word and _itoa_word, which for
32-bits pulls a lot of definitions from _itoa.c (due _ITOA_NEEDED
being defined).  To simplify the build move the required function
to a new file, _fitoa_word.c.

Checked on x86_64-linux-gnu and i686-linux-gnu.

Co-authored-by: Geoffrey Thomas <geofft@ldpreload.com>
Reviewed-by: Geoffrey Thomas <geofft@ldpreload.com>
Tested-by: Geoffrey Thomas <geofft@ldpreload.com>
This commit is contained in:
Adhemerval Zanella
2025-02-18 15:58:16 -05:00
parent dded0d20f6
commit 9b646f5dc9
13 changed files with 214 additions and 74 deletions
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3
stdio-common/Makefile
View File

@@ -59,6 +59,7 @@ headers := \
# headers
routines := \
_fitoa_word \
_itoa \
_itowa \
asprintf \
@@ -663,6 +664,8 @@ CFLAGS-dprintf.c += $(config-cflags-wno-ignored-attributes)
# off for non-shared builds.
CFLAGS-_itoa.o = $(no-stack-protector)
CFLAGS-_itoa.op = $(no-stack-protector)
CFLAGS-_fitoa_word.o = $(no-stack-protector)
CFLAGS-_fitoa_word.op = $(no-stack-protector)
CFLAGS-scanf13.c += $(test-config-cflags-wno-fortify-source)

59
stdio-common/_fitoa_word.c Normal file
View File

@@ -0,0 +1,59 @@
/* Internal function for converting integers to ASCII.
Copyright (C) 1994-2025 Free Software Foundation, Inc.
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
<https://www.gnu.org/licenses/>. */
#include <_itoa.h>
char *
_itoa_word (_ITOA_WORD_TYPE value, char *buflim,
unsigned int base, int upper_case)
{
const char *digits = (upper_case
? _itoa_upper_digits
: _itoa_lower_digits);
switch (base)
{
#define SPECIAL(Base) \
case Base: \
do \
*--buflim = digits[value % Base]; \
while ((value /= Base) != 0); \
break
SPECIAL (10);
SPECIAL (16);
SPECIAL (8);
default:
do
*--buflim = digits[value % base];
while ((value /= base) != 0);
}
return buflim;
}
#undef SPECIAL
char *
_fitoa_word (_ITOA_WORD_TYPE value, char *buf, unsigned int base,
int upper_case)
{
char tmpbuf[sizeof (value) * 4]; /* Worst case length: base 2. */
char *cp = _itoa_word (value, tmpbuf + sizeof (value) * 4, base, upper_case);
while (cp < tmpbuf + sizeof (value) * 4)
*buf++ = *cp++;
return buf;
}

43
stdio-common/_itoa.c
View File

@@ -162,38 +162,6 @@ const struct base_table_t _itoa_base_table[] attribute_hidden =
};
#endif
#if IS_IN (libc)
char *
_itoa_word (_ITOA_WORD_TYPE value, char *buflim,
unsigned int base, int upper_case)
{
const char *digits = (upper_case
? _itoa_upper_digits
: _itoa_lower_digits);
switch (base)
{
#define SPECIAL(Base) \
case Base: \
do \
*--buflim = digits[value % Base]; \
while ((value /= Base) != 0); \
break
SPECIAL (10);
SPECIAL (16);
SPECIAL (8);
default:
do
*--buflim = digits[value % base];
while ((value /= base) != 0);
}
return buflim;
}
#undef SPECIAL
#endif /* IS_IN (libc) */
#if _ITOA_NEEDED
char *
_itoa (unsigned long long int value, char *buflim, unsigned int base,
@@ -460,17 +428,6 @@ _itoa (unsigned long long int value, char *buflim, unsigned int base,
}
#endif
char *
_fitoa_word (_ITOA_WORD_TYPE value, char *buf, unsigned int base,
int upper_case)
{
char tmpbuf[sizeof (value) * 4]; /* Worst case length: base 2. */
char *cp = _itoa_word (value, tmpbuf + sizeof (value) * 4, base, upper_case);
while (cp < tmpbuf + sizeof (value) * 4)
*buf++ = *cp++;
return buf;
}
#if _ITOA_NEEDED
char *
_fitoa (unsigned long long value, char *buf, unsigned int base, int upper_case)