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LoadPin: Refactor sysctl initialization

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In preparation for shifting root mount when not enforcing, split sysctl
logic out into a separate helper, and unconditionally register the
sysctl, but only make it writable when the device is writable.

Cc: Paul Moore <paul@paul-moore.com>
Cc: James Morris <jmorris@namei.org>
Cc: "Serge E. Hallyn" <serge@hallyn.com>
Cc: linux-security-module@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Serge Hallyn <serge@hallyn.com>
Link: https://lore.kernel.org/r/20221209195746.1366607-2-keescook@chromium.org
This commit is contained in:
Kees Cook 2022-12-09 11:57:43 -08:00
parent b76ded2146
commit 60ba1028fc
1 changed files with 19 additions and 16 deletions
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35
security/loadpin/loadpin.c
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@ -52,7 +52,6 @@ static bool deny_reading_verity_digests;
#endif
#ifdef CONFIG_SYSCTL
static struct ctl_path loadpin_sysctl_path[] = {
{ .procname = "kernel", },
{ .procname = "loadpin", },
@ -66,18 +65,29 @@ static struct ctl_table loadpin_sysctl_table[] = {
.maxlen = sizeof(int),
.mode = 0644,
.proc_handler = proc_dointvec_minmax,
.extra1 = SYSCTL_ZERO,
.extra1 = SYSCTL_ONE,
.extra2 = SYSCTL_ONE,
},
{ }
};
static void report_writable(struct super_block *mnt_sb, bool writable)
static void set_sysctl(bool is_writable)
{
/*
* If load pinning is not enforced via a read-only block
* device, allow sysctl to change modes for testing.
*/
if (is_writable)
loadpin_sysctl_table[0].extra1 = SYSCTL_ZERO;
else
loadpin_sysctl_table[0].extra1 = SYSCTL_ONE;
}
#else
static inline void set_sysctl(bool is_writable) { }
#endif
static void report_writable(struct super_block *mnt_sb, bool writable)
{
if (mnt_sb->s_bdev) {
pr_info("%pg (%u:%u): %s\n", mnt_sb->s_bdev,
MAJOR(mnt_sb->s_bdev->bd_dev),
@ -86,21 +96,9 @@ static void report_writable(struct super_block *mnt_sb, bool writable)
} else
pr_info("mnt_sb lacks block device, treating as: writable\n");
if (writable) {
if (!register_sysctl_paths(loadpin_sysctl_path,
loadpin_sysctl_table))
pr_notice("sysctl registration failed!\n");
else
pr_info("enforcement can be disabled.\n");
} else
if (!writable)
pr_info("load pinning engaged.\n");
}
#else
static void report_writable(struct super_block *mnt_sb, bool writable)
{
pr_info("load pinning engaged.\n");
}
#endif
/*
* This must be called after early kernel init, since then the rootdev
@ -172,6 +170,7 @@ static int loadpin_check(struct file *file, enum kernel_read_file_id id)
*/
spin_unlock(&pinned_root_spinlock);
report_writable(pinned_root, load_root_writable);
set_sysctl(load_root_writable);
report_load(origin, file, "pinned");
} else {
spin_unlock(&pinned_root_spinlock);
@ -259,6 +258,10 @@ static int __init loadpin_init(void)
pr_info("ready to pin (currently %senforcing)\n",
enforce ? "" : "not ");
parse_exclude();
#ifdef CONFIG_SYSCTL
if (!register_sysctl_paths(loadpin_sysctl_path, loadpin_sysctl_table))
pr_notice("sysctl registration failed!\n");
#endif
security_add_hooks(loadpin_hooks, ARRAY_SIZE(loadpin_hooks), "loadpin");
return 0;