[PATCH v2 1/2] vfs,LSM: introduce the FS_HANDLES_LSM_OPTS flag
Ondrej Mosnacek
omosnace at redhat.com
Mon May 17 13:42:00 UTC 2021
Add a new FS_HANDLES_LSM_OPTS filesystem flag to singal to VFS that the
filesystem does LSM option setting for the given mount on its own, so
the security_sb_set_mnt_opts() call in vfs_get_tree() can be skipped.
This allows the following simplifications:
1. Removal of explicit LSM option handling from BTRFS.
This exists only because of the double-layer mount that BTRFS is
doing for its subvolume support. Setting FS_HANDLES_LSM_OPTS on the
inner layer (btrfs_root_fs_type) and unsetting FS_BINARY_MOUNTDATA
from both layers allows us to leave the LSM option handling entirely
on VFS as part of the outer vfs_get_tree() call.
2. Removal of FS_BINARY_MOUNTDATA flags from BTRFS's fs_types.
After applying (1.), we can let VFS eat away LSM opts at the outer
mount layer and then do selinux_set_mnt_opts() with these opts, so
setting the flag is no longer needed neither for preserving the LSM
opts, nor for the SELinux double-set_mnt_opts exception.
3. Removal of the ugly FS_BINARY_MOUNTDATA special case from
selinux_set_mnt_opts().
Applying (1.) and also setting FS_HANDLES_LSM_OPTS on NFS fs_types
(which needs to unavoidably do the LSM options handling on its own
due to the SECURITY_LSM_NATIVE_LABELS flag usage) gets us to the
state where there is an exactly one security_sb_set_mnt_opts() or
security_sb_clone_mnt_opts() call for each superblock, so the rather
hacky FS_BINARY_MOUNTDATA special case can be finally removed from
security_sb_set_mnt_opts().
The only other filesystem that sets FS_BINARY_MOUNTDATA is coda, which
is also the only one that has binary mount data && doesn't do its own
LSM options handling. So for coda we leave FS_HANDLES_LSM_OPTS unset and
the behavior remains unchanged - with fsconfig(2) it (probably) won't
even mount and with mount(2) it still won't support LSM options (and the
security_sb_set_mnt_opts() will be always performed with empty LSM
options as before).
AFAICT, this shouldn't negatively affect the other LSMs. In fact, I
think AppArmor will now gain the ability to do its DFA matching on BTRFS
mount options, which was prevented before due to FS_BINARY_MOUNTDATA
being set on both its fs_types.
Signed-off-by: Ondrej Mosnacek <omosnace at redhat.com>
---
fs/btrfs/super.c | 34 +++++-----------------------------
fs/nfs/fs_context.c | 6 ++++--
fs/super.c | 10 ++++++----
include/linux/fs.h | 3 ++-
security/selinux/hooks.c | 15 ---------------
5 files changed, 17 insertions(+), 51 deletions(-)
diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 4a396c1147f1..80716ead1cde 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -1666,19 +1666,12 @@ static struct dentry *btrfs_mount_root(struct file_system_type *fs_type,
struct btrfs_device *device = NULL;
struct btrfs_fs_devices *fs_devices = NULL;
struct btrfs_fs_info *fs_info = NULL;
- void *new_sec_opts = NULL;
fmode_t mode = FMODE_READ;
int error = 0;
if (!(flags & SB_RDONLY))
mode |= FMODE_WRITE;
- if (data) {
- error = security_sb_eat_lsm_opts(data, &new_sec_opts);
- if (error)
- return ERR_PTR(error);
- }
-
/*
* Setup a dummy root and fs_info for test/set super. This is because
* we don't actually fill this stuff out until open_ctree, but we need
@@ -1688,10 +1681,9 @@ static struct dentry *btrfs_mount_root(struct file_system_type *fs_type,
* superblock with our given fs_devices later on at sget() time.
*/
fs_info = kvzalloc(sizeof(struct btrfs_fs_info), GFP_KERNEL);
- if (!fs_info) {
- error = -ENOMEM;
- goto error_sec_opts;
- }
+ if (!fs_info)
+ return ERR_PTR(-ENOMEM);
+
btrfs_init_fs_info(fs_info);
fs_info->super_copy = kzalloc(BTRFS_SUPER_INFO_SIZE, GFP_KERNEL);
@@ -1748,9 +1740,6 @@ static struct dentry *btrfs_mount_root(struct file_system_type *fs_type,
set_bit(BTRFS_FS_CSUM_IMPL_FAST, &fs_info->flags);
error = btrfs_fill_super(s, fs_devices, data);
}
- if (!error)
- error = security_sb_set_mnt_opts(s, new_sec_opts, 0, NULL);
- security_free_mnt_opts(&new_sec_opts);
if (error) {
deactivate_locked_super(s);
return ERR_PTR(error);
@@ -1762,8 +1751,6 @@ error_close_devices:
btrfs_close_devices(fs_devices);
error_fs_info:
btrfs_free_fs_info(fs_info);
-error_sec_opts:
- security_free_mnt_opts(&new_sec_opts);
return ERR_PTR(error);
}
@@ -1925,17 +1912,6 @@ static int btrfs_remount(struct super_block *sb, int *flags, char *data)
sync_filesystem(sb);
set_bit(BTRFS_FS_STATE_REMOUNTING, &fs_info->fs_state);
- if (data) {
- void *new_sec_opts = NULL;
-
- ret = security_sb_eat_lsm_opts(data, &new_sec_opts);
- if (!ret)
- ret = security_sb_remount(sb, new_sec_opts);
- security_free_mnt_opts(&new_sec_opts);
- if (ret)
- goto restore;
- }
-
ret = btrfs_parse_options(fs_info, data, *flags);
if (ret)
goto restore;
@@ -2385,7 +2361,7 @@ static struct file_system_type btrfs_fs_type = {
.name = "btrfs",
.mount = btrfs_mount,
.kill_sb = btrfs_kill_super,
- .fs_flags = FS_REQUIRES_DEV | FS_BINARY_MOUNTDATA,
+ .fs_flags = FS_REQUIRES_DEV,
};
static struct file_system_type btrfs_root_fs_type = {
@@ -2393,7 +2369,7 @@ static struct file_system_type btrfs_root_fs_type = {
.name = "btrfs",
.mount = btrfs_mount_root,
.kill_sb = btrfs_kill_super,
- .fs_flags = FS_REQUIRES_DEV | FS_BINARY_MOUNTDATA,
+ .fs_flags = FS_REQUIRES_DEV | FS_HANDLES_LSM_OPTS,
};
MODULE_ALIAS_FS("btrfs");
diff --git a/fs/nfs/fs_context.c b/fs/nfs/fs_context.c
index d95c9a39bc70..b5db4160e89b 100644
--- a/fs/nfs/fs_context.c
+++ b/fs/nfs/fs_context.c
@@ -1557,7 +1557,8 @@ struct file_system_type nfs_fs_type = {
.init_fs_context = nfs_init_fs_context,
.parameters = nfs_fs_parameters,
.kill_sb = nfs_kill_super,
- .fs_flags = FS_RENAME_DOES_D_MOVE|FS_BINARY_MOUNTDATA,
+ .fs_flags = FS_RENAME_DOES_D_MOVE|FS_BINARY_MOUNTDATA|
+ FS_HANDLES_LSM_OPTS,
};
MODULE_ALIAS_FS("nfs");
EXPORT_SYMBOL_GPL(nfs_fs_type);
@@ -1569,7 +1570,8 @@ struct file_system_type nfs4_fs_type = {
.init_fs_context = nfs_init_fs_context,
.parameters = nfs_fs_parameters,
.kill_sb = nfs_kill_super,
- .fs_flags = FS_RENAME_DOES_D_MOVE|FS_BINARY_MOUNTDATA,
+ .fs_flags = FS_RENAME_DOES_D_MOVE|FS_BINARY_MOUNTDATA|
+ FS_HANDLES_LSM_OPTS,
};
MODULE_ALIAS_FS("nfs4");
MODULE_ALIAS("nfs4");
diff --git a/fs/super.c b/fs/super.c
index 11b7e7213fd1..918c77b8c161 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -1520,10 +1520,12 @@ int vfs_get_tree(struct fs_context *fc)
smp_wmb();
sb->s_flags |= SB_BORN;
- error = security_sb_set_mnt_opts(sb, fc->security, 0, NULL);
- if (unlikely(error)) {
- fc_drop_locked(fc);
- return error;
+ if (!(fc->fs_type->fs_flags & FS_HANDLES_LSM_OPTS)) {
+ error = security_sb_set_mnt_opts(sb, fc->security, 0, NULL);
+ if (unlikely(error)) {
+ fc_drop_locked(fc);
+ return error;
+ }
}
/*
diff --git a/include/linux/fs.h b/include/linux/fs.h
index c3c88fdb9b2a..36f9cd37bc83 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2469,7 +2469,8 @@ struct file_system_type {
#define FS_HAS_SUBTYPE 4
#define FS_USERNS_MOUNT 8 /* Can be mounted by userns root */
#define FS_DISALLOW_NOTIFY_PERM 16 /* Disable fanotify permission events */
-#define FS_ALLOW_IDMAP 32 /* FS has been updated to handle vfs idmappings. */
+#define FS_ALLOW_IDMAP 32 /* FS has been updated to handle vfs idmappings. */
+#define FS_HANDLES_LSM_OPTS 64 /* FS handles LSM opts on its own - skip it in VFS */
#define FS_THP_SUPPORT 8192 /* Remove once all fs converted */
#define FS_RENAME_DOES_D_MOVE 32768 /* FS will handle d_move() during rename() internally. */
int (*init_fs_context)(struct fs_context *);
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index eaea837d89d1..041529cbf214 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -684,21 +684,6 @@ static int selinux_set_mnt_opts(struct super_block *sb,
goto out;
}
- /*
- * Binary mount data FS will come through this function twice. Once
- * from an explicit call and once from the generic calls from the vfs.
- * Since the generic VFS calls will not contain any security mount data
- * we need to skip the double mount verification.
- *
- * This does open a hole in which we will not notice if the first
- * mount using this sb set explict options and a second mount using
- * this sb does not set any security options. (The first options
- * will be used for both mounts)
- */
- if ((sbsec->flags & SE_SBINITIALIZED) && (sb->s_type->fs_flags & FS_BINARY_MOUNTDATA)
- && !opts)
- goto out;
-
root_isec = backing_inode_security_novalidate(root);
/*
--
2.31.1
More information about the Linux-security-module-archive
mailing list