selinux: fix handling of empty opts in selinux_fs_context_submount()6.56.1-60

Bug: https://bugs.gentoo.org/914204

Signed-off-by: Mike Pagano <mpagano@gentoo.org>

2 files changed, 55 insertions, 0 deletions

diff --git a/0000_README b/0000_README
index 053298cf..e0a65c77 100644
--- a/0000_README
+++ b/0000_README
@@ -263,6 +263,10 @@ Patch:  1510_fs-enable-link-security-restrictions-by-default.patch
 From:   http://sources.debian.net/src/linux/3.16.7-ckt4-3/debian/patches/debian/fs-enable-link-security-restrictions-by-default.patch/
 Desc:   Enable link security restrictions by default.
 
+Patch:  1515_selinux-fix-handling-of-empty-opts.patch
+From:   https://www.spinics.net/lists/linux-fsdevel/msg249428.html
+Desc:   selinux: fix handling of empty opts in selinux_fs_context_submount()
+
 Patch:  1700_sparc-address-warray-bound-warnings.patch
 From:		https://github.com/KSPP/linux/issues/109
 Desc:		Address -Warray-bounds warnings 
diff --git a/1515_selinux-fix-handling-of-empty-opts.patch b/1515_selinux-fix-handling-of-empty-opts.patch
new file mode 100644
index 00000000..10336ec5
--- /dev/null
+++ b/1515_selinux-fix-handling-of-empty-opts.patch
@@ -0,0 +1,51 @@
+selinux: fix handling of empty opts in selinux_fs_context_submount()
+
+selinux_set_mnt_opts() relies on the fact that the mount options pointer
+is always NULL when all options are unset (specifically in its
+!selinux_initialized() branch. However, the new
+selinux_fs_context_submount() hook breaks this rule by allocating a new
+structure even if no options are set. That causes any submount created
+before a SELinux policy is loaded to be rejected in
+selinux_set_mnt_opts().
+
+Fix this by making selinux_fs_context_submount() leave fc->security
+set to NULL when there are no options to be copied from the reference
+superblock.
+
+Reported-by: Adam Williamson <awilliam@xxxxxxxxxx>
+Link: https://bugzilla.redhat.com/show_bug.cgi?id=2236345
+Fixes: d80a8f1b58c2 ("vfs, security: Fix automount superblock LSM init problem, preventing NFS sb sharing")
+Signed-off-by: Ondrej Mosnacek <omosnace@xxxxxxxxxx>
+---
+ security/selinux/hooks.c | 10 ++++++++--
+ 1 file changed, 8 insertions(+), 2 deletions(-)
+
+diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
+index 10350534de6d6..2aa0e219d7217 100644
+--- a/security/selinux/hooks.c
++++ b/security/selinux/hooks.c
+@@ -2775,14 +2775,20 @@ static int selinux_umount(struct vfsmount *mnt, int flags)
+ static int selinux_fs_context_submount(struct fs_context *fc,
+ 				   struct super_block *reference)
+ {
+-	const struct superblock_security_struct *sbsec;
++	const struct superblock_security_struct *sbsec = selinux_superblock(reference);
+ 	struct selinux_mnt_opts *opts;
+ 
++	/*
++	 * Ensure that fc->security remains NULL when no options are set
++	 * as expected by selinux_set_mnt_opts().
++	 */
++	if (!(sbsec->flags & (FSCONTEXT_MNT|CONTEXT_MNT|DEFCONTEXT_MNT)))
++		return 0;
++
+ 	opts = kzalloc(sizeof(*opts), GFP_KERNEL);
+ 	if (!opts)
+ 		return -ENOMEM;
+ 
+-	sbsec = selinux_superblock(reference);
+ 	if (sbsec->flags & FSCONTEXT_MNT)
+ 		opts->fscontext_sid = sbsec->sid;
+ 	if (sbsec->flags & CONTEXT_MNT)
+-- 
+2.41.0