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Landlock: Workaround a bug in RHEL 9 kernel

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If one runs xz 5.8.0 or 5.8.1 from some other distribution in a container
on RHEL 9, xz will fail with the message "Failed to enable the sandbox".

RHEL 9 kernel since 5.14.0-603.el9 (2025-07-30) claims to support
Landlock ABI version 6, but it lacks support for LANDLOCK_SCOPE_SIGNAL.
The issue is still present in 5.14.0-643.el9 (2025-11-22). Red Hat is
aware of the issue, but I don't know when it will be fixed.

The sandbox is meant to be transparent to users, thus there isn't and
won't be a command line option to disable it. Instead, add a workaround
to keep xz working on the buggy RHEL 9 kernels.

Reported-by: Richard W.M. Jones
Thanks-to: Pavel Raiskup
Tested-by: Orgad Shaneh
Tested-by: Richard W.M. Jones
Fixes: https://github.com/tukaani-project/xz/issues/199
Link: https://issues.redhat.com/browse/RHEL-125143
Link: https://bugzilla.redhat.com/show_bug.cgi?id=2407105
Link: https://lists.fedoraproject.org/archives/list/devel@lists.fedoraproject.org/message/65BDSY56R5ZJRTUC4B6CIVCVLY4LG4ME/
This commit is contained in:
Lasse Collin 2025-11-23 20:13:49 +02:00
parent ee75c76958
commit 2b2652e914
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GPG Key ID: 38EE757D69184620
1 changed files with 26 additions and 1 deletions
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27
src/common/my_landlock.h
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@ -21,6 +21,7 @@
#include <linux/landlock.h>
#include <sys/syscall.h>
#include <sys/prctl.h>
#include <sys/utsname.h>
/// \brief Initialize Landlock ruleset attributes to forbid everything
@ -42,10 +43,28 @@ my_landlock_ruleset_attr_forbid_all(struct landlock_ruleset_attr *attr)
// >0 = Landlock ABI version
static int abi_version = 0;
if (abi_version == 0)
// Red Hat Enterprise Linux 9 kernel since 5.14.0-603.el9 (2025-07-30)
// claims ABI version 6 support, but as of 5.14.0-643.el9 (2025-11-22)
// it lacks LANDLOCK_SCOPE_SIGNAL. ABI version 6 was added in upstream
// Linux 6.12 while RHEL 9 has Linux 5.14 with lots of backports.
// We assume that any kernel version 5.14 with ABI version 6 is buggy.
static bool is_rhel9 = false;
if (abi_version == 0) {
abi_version = syscall(SYS_landlock_create_ruleset,
(void *)NULL, 0, LANDLOCK_CREATE_RULESET_VERSION);
if (abi_version == 6) {
static const char rel[] = "5.14.";
const size_t rel_len = sizeof(rel) - 1;
struct utsname un;
if (uname(&un) == 0 && strncmp(
un.release, rel, rel_len) == 0)
is_rhel9 = true;
}
}
if (abi_version <= 0)
return -1;
@ -121,6 +140,12 @@ my_landlock_ruleset_attr_forbid_all(struct landlock_ruleset_attr *attr)
#endif
FALLTHROUGH;
case 6:
if (is_rhel9)
attr->scoped &= ~LANDLOCK_SCOPE_SIGNAL;
FALLTHROUGH;
default:
// We only know about the features of the ABIs 1-6.
break;