Add two parameter to specify how many times a kexec kernel can be loaded.
These parameter allow hardening the system.
While we are at it, fix a documentation issue and refactor some code.
To: Jonathan Corbet <[email protected]>
To: Eric Biederman <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: Joel Fernandes (Google) <[email protected]>
Cc: Sergey Senozhatsky <[email protected]>
Cc: Steven Rostedt <[email protected]>
Cc: Ross Zwisler <[email protected]>
To: Philipp Rudo <[email protected]>
To: Guilherme G. Piccoli <[email protected]>
Signed-off-by: Ricardo Ribalda <[email protected]>
---
Changes in v4 (Thanks Steven!):
- Uses sysctl instead or module_parameters
- Pass image type instead of boolean to permitted
- Fix typo on flag handling
- Return -EINVAL for values that does not change the current value.
- Link to v3: https://lore.kernel.org/r/[email protected]
Changes in v3:
- s/paramter/parameter/ Thanks Ghilherme!
- s/permited/permitted/ Thanks Joel!
- Link to v2: https://lore.kernel.org/r/[email protected]
Changes in v2:
- Instead of kexec_reboot_disabled, add two new counters (Thanks Philipp!)
- Link to v1: https://lore.kernel.org/r/[email protected]
---
Ricardo Ribalda (3):
Documentation: sysctl: Correct kexec_load_disabled
kexec: Factor out kexec_load_permitted
kexec: Introduce sysctl parameters kexec_load_limit_*
Documentation/admin-guide/sysctl/kernel.rst | 25 +++++++-
include/linux/kexec.h | 3 +-
kernel/kexec.c | 4 +-
kernel/kexec_core.c | 96 ++++++++++++++++++++++++++++-
kernel/kexec_file.c | 11 ++--
5 files changed, 129 insertions(+), 10 deletions(-)
---
base-commit: 479174d402bcf60789106eedc4def3957c060bad
change-id: 20221114-disable-kexec-reset-19b7e117338f
Best regards,
--
Ricardo Ribalda <[email protected]>
kexec_load_disabled affects both ``kexec_load`` and ``kexec_file_load``
syscalls. Make it explicit.
Signed-off-by: Ricardo Ribalda <[email protected]>
---
Documentation/admin-guide/sysctl/kernel.rst | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)
diff --git a/Documentation/admin-guide/sysctl/kernel.rst b/Documentation/admin-guide/sysctl/kernel.rst
index 98d1b198b2b4..97394bd9d065 100644
--- a/Documentation/admin-guide/sysctl/kernel.rst
+++ b/Documentation/admin-guide/sysctl/kernel.rst
@@ -450,9 +450,10 @@ this allows system administrators to override the
kexec_load_disabled
===================
-A toggle indicating if the ``kexec_load`` syscall has been disabled.
-This value defaults to 0 (false: ``kexec_load`` enabled), but can be
-set to 1 (true: ``kexec_load`` disabled).
+A toggle indicating if the syscalls ``kexec_load`` and
+``kexec_file_load`` have been disabled.
+This value defaults to 0 (false: ``kexec_*load`` enabled), but can be
+set to 1 (true: ``kexec_*load`` disabled).
Once true, kexec can no longer be used, and the toggle cannot be set
back to false.
This allows a kexec image to be loaded before disabling the syscall,
--
2.39.0.314.g84b9a713c41-goog-b4-0.11.0-dev-696ae
Both syscalls (kexec and kexec_file) do the same check, lets factor it
out.
Signed-off-by: Ricardo Ribalda <[email protected]>
---
include/linux/kexec.h | 3 ++-
kernel/kexec.c | 2 +-
kernel/kexec_core.c | 11 ++++++++++-
kernel/kexec_file.c | 2 +-
4 files changed, 14 insertions(+), 4 deletions(-)
diff --git a/include/linux/kexec.h b/include/linux/kexec.h
index 41a686996aaa..182e0c11b87b 100644
--- a/include/linux/kexec.h
+++ b/include/linux/kexec.h
@@ -406,7 +406,8 @@ extern int kimage_crash_copy_vmcoreinfo(struct kimage *image);
extern struct kimage *kexec_image;
extern struct kimage *kexec_crash_image;
-extern int kexec_load_disabled;
+
+bool kexec_load_permitted(void);
#ifndef kexec_flush_icache_page
#define kexec_flush_icache_page(page)
diff --git a/kernel/kexec.c b/kernel/kexec.c
index cb8e6e6f983c..ce1bca874a8d 100644
--- a/kernel/kexec.c
+++ b/kernel/kexec.c
@@ -193,7 +193,7 @@ static inline int kexec_load_check(unsigned long nr_segments,
int result;
/* We only trust the superuser with rebooting the system. */
- if (!capable(CAP_SYS_BOOT) || kexec_load_disabled)
+ if (!kexec_load_permitted())
return -EPERM;
/* Permit LSMs and IMA to fail the kexec */
diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
index ca2743f9c634..a1efc70f4158 100644
--- a/kernel/kexec_core.c
+++ b/kernel/kexec_core.c
@@ -928,7 +928,7 @@ int kimage_load_segment(struct kimage *image,
struct kimage *kexec_image;
struct kimage *kexec_crash_image;
-int kexec_load_disabled;
+static int kexec_load_disabled;
#ifdef CONFIG_SYSCTL
static struct ctl_table kexec_core_sysctls[] = {
{
@@ -952,6 +952,15 @@ static int __init kexec_core_sysctl_init(void)
late_initcall(kexec_core_sysctl_init);
#endif
+bool kexec_load_permitted(void)
+{
+ /*
+ * Only the superuser can use the kexec syscall and if it has not
+ * been disabled.
+ */
+ return capable(CAP_SYS_BOOT) && !kexec_load_disabled;
+}
+
/*
* No panic_cpu check version of crash_kexec(). This function is called
* only when panic_cpu holds the current CPU number; this is the only CPU
diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
index 45637511e0de..29efa43ea951 100644
--- a/kernel/kexec_file.c
+++ b/kernel/kexec_file.c
@@ -330,7 +330,7 @@ SYSCALL_DEFINE5(kexec_file_load, int, kernel_fd, int, initrd_fd,
struct kimage **dest_image, *image;
/* We only trust the superuser with rebooting the system. */
- if (!capable(CAP_SYS_BOOT) || kexec_load_disabled)
+ if (!kexec_load_permitted())
return -EPERM;
/* Make sure we have a legal set of flags */
--
2.39.0.314.g84b9a713c41-goog-b4-0.11.0-dev-696ae