[PATCH v3] libdwfl: resolve all paths relative to sysroot
Michal Sekletar
msekleta@redhat.com
Mon Jun 2 12:46:20 GMT 2025
Whenever possible, resolve all symlinks as if the sysroot path were a
chroot environment. This prevents potential interactions with files from
the host filesystem.
Signed-off-by: Michal Sekletar <msekleta@redhat.com>
---
configure.ac | 26 ++++++++++++++++
libdwfl/dwfl_segment_report_module.c | 44 +++++++++++++++++++++++-----
libdwfl/link_map.c | 37 ++++++++++++++++++++++-
tests/run-sysroot.sh | 34 +++++++++++++++++++++
4 files changed, 132 insertions(+), 9 deletions(-)
diff --git a/configure.ac b/configure.ac
index 0670e01a..b8531aa7 100644
--- a/configure.ac
+++ b/configure.ac
@@ -279,6 +279,32 @@ case "$CFLAGS" in
;;
esac
+AC_CACHE_CHECK(
+ [for openat2 with RESOLVE_IN_ROOT support],
+ [eu_cv_openat2_RESOLVE_IN_ROOT],
+ [AC_LINK_IFELSE(
+ [AC_LANG_PROGRAM(
+ [[#define _GNU_SOURCE
+ #include <fcntl.h>
+ #include <stdlib.h>
+ #include <unistd.h>
+ #include <sys/syscall.h>
+ #include <linux/openat2.h>
+ #include <stdio.h>
+ ]], [[
+ struct open_how how = { .flags = O_RDONLY|O_DIRECTORY, .resolve = RESOLVE_IN_ROOT };
+ int dfd = open (".", O_PATH);
+ return syscall (SYS_openat2, dfd, ".", &how, sizeof(how)) < 0;
+ ]]
+ )],
+ [eu_cv_openat2_RESOLVE_IN_ROOT=yes],
+ [eu_cv_openat2_RESOLVE_IN_ROOT=no]
+ )]
+)
+AS_IF([test "x$eu_cv_openat2_RESOLVE_IN_ROOT" = xyes],
+ [AC_DEFINE([HAVE_OPENAT2_RESOLVE_IN_ROOT], [1], [Define if openat2 is available])]
+)
+
dnl enable debugging of branch prediction.
AC_ARG_ENABLE([debugpred],
AS_HELP_STRING([--enable-debugpred],[build binaries with support to debug branch prediction]),
diff --git a/libdwfl/dwfl_segment_report_module.c b/libdwfl/dwfl_segment_report_module.c
index 32f44af8..f2f866c2 100644
--- a/libdwfl/dwfl_segment_report_module.c
+++ b/libdwfl/dwfl_segment_report_module.c
@@ -37,6 +37,12 @@
#include <inttypes.h>
#include <fcntl.h>
+#ifdef HAVE_OPENAT2_RESOLVE_IN_ROOT
+#include <linux/openat2.h>
+#include <sys/syscall.h>
+#include <unistd.h>
+#endif
+
#include <system.h>
@@ -783,17 +789,39 @@ dwfl_segment_report_module (Dwfl *dwfl, int ndx, const char *name,
/* We were not handed specific executable hence try to look for it in
sysroot if it is set. */
if (dwfl->sysroot && !executable)
- {
- int r;
- char *n;
+ {
+#ifdef HAVE_OPENAT2_RESOLVE_IN_ROOT
+ int sysrootfd, err;
+
+ struct open_how how = {
+ .flags = O_RDONLY,
+ .resolve = RESOLVE_IN_ROOT,
+ };
+
+ sysrootfd = open (dwfl->sysroot, O_DIRECTORY|O_PATH);
+ if (sysrootfd < 0)
+ return -1;
+
+ fd = syscall (SYS_openat2, sysrootfd, name, &how, sizeof(how));
+ err = fd < 0 ? -errno : 0;
- r = asprintf (&n, "%s%s", dwfl->sysroot, name);
- if (r > 0)
+ close (sysrootfd);
+
+ /* Fallback to regular open() if openat2 is not available. */
+ if (fd < 0 && err == -ENOSYS)
+#endif
{
- fd = open (n, O_RDONLY);
- free (n);
+ int r;
+ char *n;
+
+ r = asprintf (&n, "%s%s", dwfl->sysroot, name);
+ if (r > 0)
+ {
+ fd = open (n, O_RDONLY);
+ free (n);
+ }
}
- }
+ }
else
fd = open (name, O_RDONLY);
diff --git a/libdwfl/link_map.c b/libdwfl/link_map.c
index 8ab14862..013a415d 100644
--- a/libdwfl/link_map.c
+++ b/libdwfl/link_map.c
@@ -34,6 +34,12 @@
#include <fcntl.h>
+#ifdef HAVE_OPENAT2_RESOLVE_IN_ROOT
+#include <linux/openat2.h>
+#include <sys/syscall.h>
+#include <unistd.h>
+#endif
+
/* This element is always provided and always has a constant value.
This makes it an easy thing to scan for to discern the format. */
#define PROBE_TYPE AT_PHENT
@@ -418,19 +424,48 @@ report_r_debug (uint_fast8_t elfclass, uint_fast8_t elfdata,
/* This code is mostly inlined dwfl_report_elf. */
char *sysroot_name = NULL;
const char *sysroot = dwfl->sysroot;
+ int fd;
/* Don't use the sysroot if the path is already inside it. */
bool name_in_sysroot = sysroot && startswith (name, sysroot);
if (sysroot && !name_in_sysroot)
{
+ const char *n = NULL;
+
if (asprintf (&sysroot_name, "%s%s", sysroot, name) < 0)
return release_buffer (&memory_closure, &buffer, &buffer_available, -1);
+ n = name;
name = sysroot_name;
+
+#ifdef HAVE_OPENAT2_RESOLVE_IN_ROOT
+ int sysrootfd, err;
+
+ struct open_how how = {
+ .flags = O_RDONLY,
+ .resolve = RESOLVE_IN_ROOT,
+ };
+
+ sysrootfd = open (sysroot, O_DIRECTORY|O_PATH);
+ if (sysrootfd < 0)
+ return -1;
+
+ fd = syscall (SYS_openat2, sysrootfd, n, &how, sizeof(how));
+ err = fd < 0 ? -errno : 0;
+
+ close (sysrootfd);
+
+ /* Fallback to regular open() if openat2 is not available. */
+ if (fd < 0 && err == -ENOSYS)
+#endif
+ {
+ fd = open (name, O_RDONLY);
+ }
}
+ else
+ fd = open (name, O_RDONLY);
- int fd = open (name, O_RDONLY);
if (fd >= 0)
{
Elf *elf;
diff --git a/tests/run-sysroot.sh b/tests/run-sysroot.sh
index 1dc079cd..fe302446 100755
--- a/tests/run-sysroot.sh
+++ b/tests/run-sysroot.sh
@@ -46,4 +46,38 @@ TID 431185:
#8 0x0000aaaae56127f0 _start
EOF
+HAVE_OPENAT2=$(grep '^#define HAVE_OPENAT2_RESOLVE_IN_ROOT' \
+ ${abs_builddir}/../config.h | awk '{print $3}')
+
+if [[ "$HAVE_OPENAT2" = 1 ]]; then
+ # Change the layout of files in sysroot to test symlink escape scenario
+ rm -f "${tmpdir}/sysroot/bin"
+ mkdir "${tmpdir}/sysroot/bin"
+ mv "${tmpdir}/sysroot/usr/bin/bash" "${tmpdir}/sysroot/bin/bash"
+ ln -s /bin/bash "${tmpdir}/sysroot/usr/bin/bash"
+
+ # Check that stack with --sysroot generates correct backtrace even if target
+ # binary is actually absolute symlink pointing outside of sysroot directory
+ testrun "${abs_top_builddir}"/src/stack --core "${tmpdir}/core.bash" \
+ --sysroot "${tmpdir}/sysroot" >"${tmpdir}/stack.out"
+
+ # Remove 2 stack frames with symbol names contained in .gnu_debugdata.
+ # Whether or not these names appear in the output depends on if elfutils
+ # was built with LZMA support.
+ sed -i '4,5d' "${tmpdir}/stack.out"
+
+ # Check that we are able to get fully symbolized backtrace
+ testrun_compare cat "${tmpdir}/stack.out" <<\EOF
+PID 431185 - core
+TID 431185:
+#0 0x0000ffff8ebe5a8c kill
+#3 0x0000aaaae562b2fc execute_command
+#4 0x0000aaaae561cbb4 reader_loop
+#5 0x0000aaaae5611bf0 main
+#6 0x0000ffff8ebd09dc __libc_start_call_main
+#7 0x0000ffff8ebd0ab0 __libc_start_main@@GLIBC_2.34
+#8 0x0000aaaae56127f0 _start
+EOF
+fi
+
exit_cleanup
--
2.39.5 (Apple Git-154)
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