You can get ENOTSUP due to the system not supporting chmod(symlink),
but you can also get ENOTSUP on any file type if the system needs
/proc to emulate AT_SYMLINK_NOFOLLOW and /proc is not available.
This emulation is used before Linux 6.6 (2023).
* src/chmod.c (process_file): Check we're operating on a symlink
if we get ENOTSUP, and only ignore the error in that case.
* tests/chmod/symlink-enotsup.sh: Add a new test.
* tests/local.mk: Reference the new test.
* NEWS: Mention the bug fix.
Discovered by Anthropic's OSS Scanner, as bug ANT-2026-PSCKLNL1.
---
NEWS | 5 ++++
src/chmod.c | 20 +++++++++++--
tests/chmod/symlink-enotsup.sh | 54 ++++++++++++++++++++++++++++++++++
tests/local.mk | 1 +
4 files changed, 77 insertions(+), 3 deletions(-)
create mode 100755 tests/chmod/symlink-enotsup.sh
diff --git a/NEWS b/NEWS
index b288a6bf5..3f4d4184d 100644
--- a/NEWS
+++ b/NEWS
@@ -15,6 +15,11 @@ GNU coreutils NEWS -*-
outline -*-
when only a partial context is specified.
[bug introduced with the chcon program in coreutils-6.9.90]
+ 'chmod -R' and 'chmod -h' no longer silently skip permission changes on
+ files and directories on Linux kernels before 6.6 when /proc is unavailable.
+ These operations now diagnose the unsupported changes and exit with failure.
+ [bug introduced in coreutils-9.5]
+
'chmod -R --dereference --preserve-root' no longer silently skips the
entry following a symbolic link to '/' encountered during traversal.
[bug introduced in coreutils-9.5]
diff --git a/src/chmod.c b/src/chmod.c
index 58310157f..5a7b41c2b 100644
--- a/src/chmod.c
+++ b/src/chmod.c
@@ -27,6 +27,7 @@
#include "filemode.h"
#include "fts-missing.h"
#include "ignore-value.h"
+#include "issymlinkat.h"
#include "modechange.h"
#include "quote.h"
#include "root-dev-ino.h"
@@ -329,13 +330,26 @@ process_file (FTS *fts, FTSENT *ent)
ch.status = CH_SUCCEEDED;
else
{
+ int chmod_errno = errno;
if (ignore_missing
- && ignorable_traversal_errno (errno))
+ && ignorable_traversal_errno (chmod_errno))
return true;
- if (! is_ENOTSUP (errno))
+ /* Ignore unsupported changes only for symlinks themselves.
+ Older systems (without /proc) may return ENOTSUP for non symlinks.
+ FTS may have supplied referent metadata, so check again. */
+ bool unsupported_symlink = false;
+ if (is_ENOTSUP (chmod_errno) && ! follow_symlink)
+ {
+ int is_symlink = issymlinkat (fts->fts_cwd_fd, file);
+ if (is_symlink < 0 && ignore_missing
+ && ignorable_traversal_errno (errno))
+ return true;
+ unsupported_symlink = is_symlink == 1;
+ }
+ if (! unsupported_symlink)
{
if (! force_silent)
- error (0, errno, _("changing permissions of %s"),
+ error (0, chmod_errno, _("changing permissions of %s"),
quoteaf (file_full_name));
ch.status = CH_FAILED;
diff --git a/tests/chmod/symlink-enotsup.sh b/tests/chmod/symlink-enotsup.sh
new file mode 100755
index 000000000..b3b93e770
--- /dev/null
+++ b/tests/chmod/symlink-enotsup.sh
@@ -0,0 +1,54 @@
+#!/bin/sh
+# Ignore ENOTSUP only when changing a symlink itself.
+
+# Copyright (C) 2026 Free Software Foundation, Inc.
+
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+
+# This program 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 General Public License for more details.
+
+# You should have received a copy of the GNU General Public License
+# along with this program. If not, see <https://www.gnu.org/licenses/>.
+
+. "${srcdir=.}/tests/init.sh"; path_prepend_ ./src
+print_ver_ chmod
+require_strace_ chmod
+getlimits_
+
+# Match all chmod variants, including fchmodat2 when supported.
+inject='/.*chmod:error=EOPNOTSUPP'
+strace --quiet=all -o /dev/null -e inject="$inject" true 2>/dev/null \
+ || skip_ 'strace does not support the required injection options'
+
+touch file || framework_failure_
+ln -s file link || framework_failure_
+
+for deref in --dereference --no-dereference; do
+ for file in file link; do
+ strace --quiet=all -o trace -e inject="$inject" \
+ chmod "$deref" u+w "$file" >out 2>err
+ status=$?
+ grep ' (INJECTED)' trace > /dev/null \
+ || skip_ 'strace did not inject the requested failure'
+
+ # Only unsupported changes to the symlink itself may be ignored.
+ if test "$deref:$file" = --no-dereference:link; then
+ test "$status" = 0 || fail=1
+ compare /dev/null err || fail=1
+ else
+ test "$status" = 1 || fail=1
+ echo "chmod: changing permissions of '$file': $ENOTSUP" >exp \
+ || framework_failure_
+ compare exp err || fail=1
+ fi
+ compare /dev/null out || fail=1
+ done
+done
+
+Exit $fail
diff --git a/tests/local.mk b/tests/local.mk
index 60574262e..d905ad76e 100644
--- a/tests/local.mk
+++ b/tests/local.mk
@@ -586,6 +586,7 @@ all_tests = \
tests/chmod/thru-dangling.sh \
tests/chmod/umask-x.sh \
tests/chmod/usage.sh \
+ tests/chmod/symlink-enotsup.sh \
tests/chmod/symlinks.sh \
tests/chown/cannot-access.sh \
tests/chown/deref.sh \
--
2.56.0
