On 12/21/18 3:18 PM, Ondrej Mosnacek wrote:
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@xxxxxxxxxx>
Reviewed-by: Stephen Smalley <sds@xxxxxxxxxxxxx>
---
security/selinux/hooks.c | 40 +++++++++++++++++++++++++++++++---------
1 file changed, 31 insertions(+), 9 deletions(-)
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 7ce012d9ec51..b4759bebeddc 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -497,16 +497,10 @@ static int may_context_mount_inode_relabel(u32 sid,
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") ||
@@ -516,6 +510,34 @@ static int selinux_is_sblabel_mnt(struct super_block *sb)
!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;
