[PATCH 5.0 113/122] selinux: never allow relabeling on context mounts

Greg Kroah-Hartman
2019-05-06T15:05:32Z

From: Ondrej Mosnacek <omosnace@redhat.com>

commit a83d6ddaebe541570291205cb538e35ad4ff94f9 upstream.

In the SECURITY_FS_USE_MNTPOINT case we never want to allow relabeling
files/directories, so we should never set the SBLABEL_MNT flag. The
'special handling' in selinux_is_sblabel_mnt() is only intended for when
the behavior is set to SECURITY_FS_USE_GENFS.

While there, make the logic in selinux_is_sblabel_mnt() more explicit
and add a BUILD_BUG_ON() to make sure that introducing a new
SECURITY_FS_USE_* forces a review of the logic.

Fixes: d5f3a5f6e7e7 ("selinux: add security in-core xattr support for pstore and debugfs")
Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>
Reviewed-by: Stephen Smalley <sds@tycho.nsa.gov>
Signed-off-by: Paul Moore <paul@paul-moore.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
security/selinux/hooks.c | 40 +++++++++++++++++++++++++++++++---------
1 file changed, 31 insertions(+), 9 deletions(-)

--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -534,16 +534,10 @@ static int may_context_mount_inode_relab
return rc;
}

-static int selinux_is_sblabel_mnt(struct super_block *sb)
+static int selinux_is_genfs_special_handling(struct super_block *sb)
{
- struct superblock_security_struct *sbsec = sb->s_security;
-
- return sbsec->behavior == SECURITY_FS_USE_XATTR ||
- sbsec->behavior == SECURITY_FS_USE_TRANS ||
- sbsec->behavior == SECURITY_FS_USE_TASK ||
- sbsec->behavior == SECURITY_FS_USE_NATIVE ||
- /* Special handling. Genfs but also in-core setxattr handler */
- !strcmp(sb->s_type->name, "sysfs") ||
+ /* Special handling. Genfs but also in-core setxattr handler */
+ return !strcmp(sb->s_type->name, "sysfs") ||
!strcmp(sb->s_type->name, "pstore") ||
!strcmp(sb->s_type->name, "debugfs") ||
!strcmp(sb->s_type->name, "tracefs") ||
@@ -553,6 +547,34 @@ static int selinux_is_sblabel_mnt(struct
!strcmp(sb->s_type->name, "cgroup2")));
}

+static int selinux_is_sblabel_mnt(struct super_block *sb)
+{
+ struct superblock_security_struct *sbsec = sb->s_security;
+
+ /*
+ * IMPORTANT: Double-check logic in this function when adding a new
+ * SECURITY_FS_USE_* definition!
+ */
+ BUILD_BUG_ON(SECURITY_FS_USE_MAX != 7);
+
+ switch (sbsec->behavior) {
+ case SECURITY_FS_USE_XATTR:
+ case SECURITY_FS_USE_TRANS:
+ case SECURITY_FS_USE_TASK:
+ case SECURITY_FS_USE_NATIVE:
+ return 1;
+
+ case SECURITY_FS_USE_GENFS:
+ return selinux_is_genfs_special_handling(sb);
+
+ /* Never allow relabeling on context mounts */
+ case SECURITY_FS_USE_MNTPOINT:
+ case SECURITY_FS_USE_NONE:
+ default:
+ return 0;
+ }
+}
+
static int sb_finish_set_opts(struct super_block *sb)
{
struct superblock_security_struct *sbsec = sb->s_security;