vfs, security: Fix automount superblock LSM init problem, preventing NFS sb sharing

When NFS superblocks are created by automounting, their LSM parameters
aren't set in the fs_context struct prior to sget_fc() being called,
leading to failure to match existing superblocks.

This bug leads to messages like the following appearing in dmesg when
fscache is enabled:

    NFS: Cache volume key already in use (nfs,4.2,2,108,106a8c0,1,,,,100000,100000,2ee,3a98,1d4c,3a98,1)

Fix this by adding a new LSM hook to load fc->security for submount
creation.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Link: https://lore.kernel.org/r/165962680944.3334508.6610023900349142034.stgit@warthog.procyon.org.uk/
Link: https://lore.kernel.org/r/165962729225.3357250.14350728846471527137.stgit@warthog.procyon.org.uk/
Link: https://lore.kernel.org/r/165970659095.2812394.6868894171102318796.stgit@warthog.procyon.org.uk/
Link: https://lore.kernel.org/r/166133579016.3678898.6283195019480567275.stgit@warthog.procyon.org.uk/
Link: https://lore.kernel.org/r/217595.1662033775@warthog.procyon.org.uk/
Fixes: 9bc61ab18b1d ("vfs: Introduce fs_context, switch vfs_kern_mount() to it.")
Fixes: 779df6a5480f ("NFS: Ensure security label is set for root inode")
Tested-by: Jeff Layton <jlayton@kernel.org>
Acked-by: Casey Schaufler <casey@schaufler-ca.com>
Acked-by: "Christian Brauner (Microsoft)" <brauner@kernel.org>
Acked-by: Paul Moore <paul@paul-moore.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Message-Id: <20230808-master-v9-1-e0ecde888221@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>

diff --git a/fs/fs_context.c b/fs/fs_context.c
index 851214d1d013dce8d385dddb31f331b03e7c9bf6..375023e40161de51d48b6b8fe8345a4b38f57e42 100644 (file)
--- a/fs/fs_context.c
+++ b/fs/fs_context.c
@@ -315,10 +315,31 @@ struct fs_context *fs_context_for_reconfigure(struct dentry *dentry,
 }
 EXPORT_SYMBOL(fs_context_for_reconfigure);
 
+/**
+ * fs_context_for_submount: allocate a new fs_context for a submount
+ * @type: file_system_type of the new context
+ * @reference: reference dentry from which to copy relevant info
+ *
+ * Allocate a new fs_context suitable for a submount. This also ensures that
+ * the fc->security object is inherited from @reference (if needed).
+ */
 struct fs_context *fs_context_for_submount(struct file_system_type *type,
                                           struct dentry *reference)
 {
-       return alloc_fs_context(type, reference, 0, 0, FS_CONTEXT_FOR_SUBMOUNT);
+       struct fs_context *fc;
+       int ret;
+
+       fc = alloc_fs_context(type, reference, 0, 0, FS_CONTEXT_FOR_SUBMOUNT);
+       if (IS_ERR(fc))
+               return fc;
+
+       ret = security_fs_context_submount(fc, reference->d_sb);
+       if (ret) {
+               put_fs_context(fc);
+               return ERR_PTR(ret);
+       }
+
+       return fc;
 }
 EXPORT_SYMBOL(fs_context_for_submount);
 

diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
index 7308a1a7599b4a1335b0a208d32cfb6888224370..af796986baee6040da0424528d63d96f8a0a0837 100644 (file)
--- a/include/linux/lsm_hook_defs.h
+++ b/include/linux/lsm_hook_defs.h
@@ -54,6 +54,7 @@ LSM_HOOK(int, 0, bprm_creds_from_file, struct linux_binprm *bprm, struct file *f
 LSM_HOOK(int, 0, bprm_check_security, struct linux_binprm *bprm)
 LSM_HOOK(void, LSM_RET_VOID, bprm_committing_creds, struct linux_binprm *bprm)
 LSM_HOOK(void, LSM_RET_VOID, bprm_committed_creds, struct linux_binprm *bprm)
+LSM_HOOK(int, 0, fs_context_submount, struct fs_context *fc, struct super_block *reference)
 LSM_HOOK(int, 0, fs_context_dup, struct fs_context *fc,
         struct fs_context *src_sc)
 LSM_HOOK(int, -ENOPARAM, fs_context_parse_param, struct fs_context *fc,

diff --git a/include/linux/security.h b/include/linux/security.h
index 32828502f09eae3383e854e0ed62541dd28c9303..bac98ea18f78b37c5084cd8197baf86c46ac1257 100644 (file)
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -293,6 +293,7 @@ int security_bprm_creds_from_file(struct linux_binprm *bprm, struct file *file);
 int security_bprm_check(struct linux_binprm *bprm);
 void security_bprm_committing_creds(struct linux_binprm *bprm);
 void security_bprm_committed_creds(struct linux_binprm *bprm);
+int security_fs_context_submount(struct fs_context *fc, struct super_block *reference);
 int security_fs_context_dup(struct fs_context *fc, struct fs_context *src_fc);
 int security_fs_context_parse_param(struct fs_context *fc, struct fs_parameter *param);
 int security_sb_alloc(struct super_block *sb);
@@ -629,6 +630,11 @@ static inline void security_bprm_committed_creds(struct linux_binprm *bprm)
 {
 }
 
+static inline int security_fs_context_submount(struct fs_context *fc,
+                                          struct super_block *reference)
+{
+       return 0;
+}
 static inline int security_fs_context_dup(struct fs_context *fc,
                                          struct fs_context *src_fc)
 {

diff --git a/security/security.c b/security/security.c
index b720424ca37d9c683c757abf3433217061b3d1e2..549104a447e36fed32d322a89774434f1dd04e65 100644 (file)
--- a/security/security.c
+++ b/security/security.c
@@ -1138,6 +1138,20 @@ void security_bprm_committed_creds(struct linux_binprm *bprm)
        call_void_hook(bprm_committed_creds, bprm);
 }
 
+/**
+ * security_fs_context_submount() - Initialise fc->security
+ * @fc: new filesystem context
+ * @reference: dentry reference for submount/remount
+ *
+ * Fill out the ->security field for a new fs_context.
+ *
+ * Return: Returns 0 on success or negative error code on failure.
+ */
+int security_fs_context_submount(struct fs_context *fc, struct super_block *reference)
+{
+       return call_int_hook(fs_context_submount, 0, fc, reference);
+}
+
 /**
  * security_fs_context_dup() - Duplicate a fs_context LSM blob
  * @fc: destination filesystem context

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index d06e350fedee5f7936ce0e9bd33c8befd771f886..afd6637440418bd58d80a4777794922ea4899524 100644 (file)
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -2745,6 +2745,27 @@ static int selinux_umount(struct vfsmount *mnt, int flags)
                                   FILESYSTEM__UNMOUNT, NULL);
 }
 
+static int selinux_fs_context_submount(struct fs_context *fc,
+                                  struct super_block *reference)
+{
+       const struct superblock_security_struct *sbsec;
+       struct selinux_mnt_opts *opts;
+
+       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)
+               opts->context_sid = sbsec->mntpoint_sid;
+       if (sbsec->flags & DEFCONTEXT_MNT)
+               opts->defcontext_sid = sbsec->def_sid;
+       fc->security = opts;
+       return 0;
+}
+
 static int selinux_fs_context_dup(struct fs_context *fc,
                                  struct fs_context *src_fc)
 {
@@ -7182,6 +7203,7 @@ static struct security_hook_list selinux_hooks[] __ro_after_init = {
        /*
         * PUT "CLONING" (ACCESSING + ALLOCATING) HOOKS HERE
         */
+       LSM_HOOK_INIT(fs_context_submount, selinux_fs_context_submount),
        LSM_HOOK_INIT(fs_context_dup, selinux_fs_context_dup),
        LSM_HOOK_INIT(fs_context_parse_param, selinux_fs_context_parse_param),
        LSM_HOOK_INIT(sb_eat_lsm_opts, selinux_sb_eat_lsm_opts),

diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
index 6e270cf3fd30c7bccc23b388decf36bc77c6169f..a8201cf22f20b3de75f1071269e6456060b581b4 100644 (file)
--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -614,6 +614,56 @@ out_opt_err:
        return -EINVAL;
 }
 
+/**
+ * smack_fs_context_submount - Initialise security data for a filesystem context
+ * @fc: The filesystem context.
+ * @reference: reference superblock
+ *
+ * Returns 0 on success or -ENOMEM on error.
+ */
+static int smack_fs_context_submount(struct fs_context *fc,
+                                struct super_block *reference)
+{
+       struct superblock_smack *sbsp;
+       struct smack_mnt_opts *ctx;
+       struct inode_smack *isp;
+
+       ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
+       if (!ctx)
+               return -ENOMEM;
+       fc->security = ctx;
+
+       sbsp = smack_superblock(reference);
+       isp = smack_inode(reference->s_root->d_inode);
+
+       if (sbsp->smk_default) {
+               ctx->fsdefault = kstrdup(sbsp->smk_default->smk_known, GFP_KERNEL);
+               if (!ctx->fsdefault)
+                       return -ENOMEM;
+       }
+
+       if (sbsp->smk_floor) {
+               ctx->fsfloor = kstrdup(sbsp->smk_floor->smk_known, GFP_KERNEL);
+               if (!ctx->fsfloor)
+                       return -ENOMEM;
+       }
+
+       if (sbsp->smk_hat) {
+               ctx->fshat = kstrdup(sbsp->smk_hat->smk_known, GFP_KERNEL);
+               if (!ctx->fshat)
+                       return -ENOMEM;
+       }
+
+       if (isp->smk_flags & SMK_INODE_TRANSMUTE) {
+               if (sbsp->smk_root) {
+                       ctx->fstransmute = kstrdup(sbsp->smk_root->smk_known, GFP_KERNEL);
+                       if (!ctx->fstransmute)
+                               return -ENOMEM;
+               }
+       }
+       return 0;
+}
+
 /**
  * smack_fs_context_dup - Duplicate the security data on fs_context duplication
  * @fc: The new filesystem context.
@@ -4876,6 +4926,7 @@ static struct security_hook_list smack_hooks[] __ro_after_init = {
        LSM_HOOK_INIT(ptrace_traceme, smack_ptrace_traceme),
        LSM_HOOK_INIT(syslog, smack_syslog),
 
+       LSM_HOOK_INIT(fs_context_submount, smack_fs_context_submount),
        LSM_HOOK_INIT(fs_context_dup, smack_fs_context_dup),
        LSM_HOOK_INIT(fs_context_parse_param, smack_fs_context_parse_param),