Re: [PATCH v3] elf: Add test for locating libraries in root dir (bug 30435)

[Siddhesh Poyarekar <siddhesh@gotplt.org>]

On 2023-05-25 10:56, Qixing ksyx Xue wrote:
> When dlopen is being called, efforts have been made to improve
> future lookup performance. This includes marking a search path
> as non-existent using `stat`. However, if the root directory
> is given as a search path, there exists a bug which erroneously
> marks it as non-existing.
> 
> The bug is reproduced under the following sequence:
> 
>    1. dlopen is called to open a shared library, with at least:
>       1) a dependency 'A.so' not directly under the '/' directory
>          (e.g. /lib/A.so), and
>       2) another dependency 'B.so' resides in '/'.
>    2. for this bug to reproduce, 'A.so' should be searched *before* 'B.so'.
>    3. it first tries to find 'A.so' in /, (e.g. /A.so):
>       - this will (obviously) fail,
>       - since it's the first time we have seen the '/' directory,
>         its 'status' is 'unknown'.
>    4. `buf[buflen - namelen - 1] = '\0'` is executed:
>       - it intends to remove the leaf and its final slash,
>       - because of the speciality of '/', its buflen == namelen + 1,
>       - it erroneously clears the entire buffer.
>    6. it then calls 'stat' with the empty buffer:
>       - which will result in an error.
>    7. so it marks '/' as 'nonexisting', future lookups will not consider
>       this path.
>    8. while /B.so *does* exist, failure to look it up in the '/'
>       directory leads to a 'cannot open shared object file' error.
> 
> This patch fixes the bug by preventing 'buflen', an index to put '\0',
> from being set to 0, so that the root '/' is always kept.
> Relative search paths are always considered as 'existing' so this
> wont be affected.
> 
> Writeup by Moody Liu <mooodyhunter@outlook.com>
> 
> Suggested-by: Carlos O'Donell <carlos@redhat.com>
> Signed-off-by: Qixing ksyx Xue <qixingxue@outlook.com>

Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>

I'll test and commit this shortly.

Thanks,
Sid

> ---
>   elf/Makefile                      |  3 +++
>   elf/tst-rootdir-lib.c             | 23 +++++++++++++++++++
>   elf/tst-rootdir.c                 | 37 +++++++++++++++++++++++++++++++
>   elf/tst-rootdir.root/preclean.req |  0
>   elf/tst-rootdir.script            |  1 +
>   5 files changed, 64 insertions(+)
>   create mode 100644 elf/tst-rootdir-lib.c
>   create mode 100644 elf/tst-rootdir.c
>   create mode 100644 elf/tst-rootdir.root/preclean.req
>   create mode 100644 elf/tst-rootdir.script
> 
> diff --git a/elf/Makefile b/elf/Makefile
> index e262f3e6b1..8640138a72 100644
> --- a/elf/Makefile
> +++ b/elf/Makefile
> @@ -325,6 +325,7 @@ static-dlopen-environment = \
>     LD_LIBRARY_PATH=$(ld-library-path):$(common-objpfx)dlfcn
>   tst-tls9-static-ENV = $(static-dlopen-environment)
>   tst-single_threaded-static-dlopen-ENV = $(static-dlopen-environment)
> +tst-rootdir-ENV = LD_LIBRARY_PATH=/
>   
>   tests += \
>     argv0test \
> @@ -506,6 +507,7 @@ tests-container += \
>     tst-dlopen-tlsmodid-container \
>     tst-pldd \
>     tst-preload-pthread-libc \
> +  tst-rootdir \
>     # tests-container
>   
>   test-srcs = \
> @@ -855,6 +857,7 @@ modules-names += \
>     tst-relsort1mod1 \
>     tst-relsort1mod2 \
>     tst-ro-dynamic-mod \
> +  tst-rootdir-lib \
>     tst-single_threaded-mod1 \
>     tst-single_threaded-mod2 \
>     tst-single_threaded-mod3 \
> diff --git a/elf/tst-rootdir-lib.c b/elf/tst-rootdir-lib.c
> new file mode 100644
> index 0000000000..007c4b0095
> --- /dev/null
> +++ b/elf/tst-rootdir-lib.c
> @@ -0,0 +1,23 @@
> +/* Simple library for testing locating library in root directories.
> +   Copyright The GNU Toolchain Authors.
> +   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
> +   <http://www.gnu.org/licenses/>.  */
> +
> +const char *
> +test_func (void)
> +{
> +  return "Success";
> +}
> diff --git a/elf/tst-rootdir.c b/elf/tst-rootdir.c
> new file mode 100644
> index 0000000000..83284ea59e
> --- /dev/null
> +++ b/elf/tst-rootdir.c
> @@ -0,0 +1,37 @@
> +/* Test code for locating libraries in root directories.
> +   Copyright The GNU Toolchain Authors.
> +   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
> +   <http://www.gnu.org/licenses/>.  */
> +
> +#include <support/test-driver.h>
> +#include <support/check.h>
> +#include <dlfcn.h>
> +#include <assert.h>
> +
> +static int
> +do_test (void)
> +{
> +  void *handle = dlopen ("libtest.so", RTLD_LAZY);
> +  TEST_VERIFY_EXIT (handle != NULL);
> +  typedef const char *(test_func_t) (void);
> +  test_func_t *func = dlsym (handle, "test_func");
> +  assert (func != NULL);
> +  TEST_COMPARE_STRING (func (), "Success");
> +  dlclose (handle);
> +  return 0;
> +}
> +
> +#include <support/test-driver.c>
> diff --git a/elf/tst-rootdir.root/preclean.req b/elf/tst-rootdir.root/preclean.req
> new file mode 100644
> index 0000000000..e69de29bb2
> diff --git a/elf/tst-rootdir.script b/elf/tst-rootdir.script
> new file mode 100644
> index 0000000000..f852c0ec34
> --- /dev/null
> +++ b/elf/tst-rootdir.script
> @@ -0,0 +1 @@
> +cp $B/elf/tst-rootdir-lib.so /libtest.so