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LoadPin: Refactor read-only check into a helper

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In preparation for allowing mounts to shift when not enforced, move
read-only checking into a separate helper.

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/20221209195746.1366607-1-keescook@chromium.org
This commit is contained in:
Kees Cook 2022-12-09 11:57:42 -08:00
parent b5fc3ca395
commit b76ded2146
1 changed files with 21 additions and 12 deletions
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33
security/loadpin/loadpin.c
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@ -72,28 +72,21 @@ static struct ctl_table loadpin_sysctl_table[] = {
{ }
};
/*
* This must be called after early kernel init, since then the rootdev
* is available.
*/
static void check_pinning_enforcement(struct super_block *mnt_sb)
static void report_writable(struct super_block *mnt_sb, bool writable)
{
bool ro = false;
/*
* If load pinning is not enforced via a read-only block
* device, allow sysctl to change modes for testing.
*/
if (mnt_sb->s_bdev) {
ro = bdev_read_only(mnt_sb->s_bdev);
pr_info("%pg (%u:%u): %s\n", mnt_sb->s_bdev,
MAJOR(mnt_sb->s_bdev->bd_dev),
MINOR(mnt_sb->s_bdev->bd_dev),
ro ? "read-only" : "writable");
writable ? "writable" : "read-only");
} else
pr_info("mnt_sb lacks block device, treating as: writable\n");
if (!ro) {
if (writable) {
if (!register_sysctl_paths(loadpin_sysctl_path,
loadpin_sysctl_table))
pr_notice("sysctl registration failed!\n");
@ -103,12 +96,26 @@ static void check_pinning_enforcement(struct super_block *mnt_sb)
pr_info("load pinning engaged.\n");
}
#else
static void check_pinning_enforcement(struct super_block *mnt_sb)
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
* is available.
*/
static bool sb_is_writable(struct super_block *mnt_sb)
{
bool writable = true;
if (mnt_sb->s_bdev)
writable = !bdev_read_only(mnt_sb->s_bdev);
return writable;
}
static void loadpin_sb_free_security(struct super_block *mnt_sb)
{
/*
@ -126,6 +133,7 @@ static int loadpin_check(struct file *file, enum kernel_read_file_id id)
{
struct super_block *load_root;
const char *origin = kernel_read_file_id_str(id);
bool load_root_writable;
/* If the file id is excluded, ignore the pinning. */
if ((unsigned int)id < ARRAY_SIZE(ignore_read_file_id) &&
@ -146,6 +154,7 @@ static int loadpin_check(struct file *file, enum kernel_read_file_id id)
}
load_root = file->f_path.mnt->mnt_sb;
load_root_writable = sb_is_writable(load_root);
/* First loaded module/firmware defines the root for all others. */
spin_lock(&pinned_root_spinlock);
@ -162,7 +171,7 @@ static int loadpin_check(struct file *file, enum kernel_read_file_id id)
* enforcing. This would be purely cosmetic.
*/
spin_unlock(&pinned_root_spinlock);
check_pinning_enforcement(pinned_root);
report_writable(pinned_root, load_root_writable);
report_load(origin, file, "pinned");
} else {
spin_unlock(&pinned_root_spinlock);