On Sat, 2023-08-05 at 14:43 +0200, Christian Brauner wrote: > On Fri, Aug 04, 2023 at 12:09:34PM -0400, Jeff Layton wrote: > > From: David Howells <dhowells@xxxxxxxxxx> > > > > 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 when alloc_fs_context() is creating the fs_context for it. > > > > Signed-off-by: David Howells <dhowells@xxxxxxxxxx> > > Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx> > > 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@xxxxxxxxxx> > > Reviewed-by: Jeff Layton <jlayton@xxxxxxxxxx> > > Acked-by: Casey Schaufler <casey@xxxxxxxxxxxxxxxx> > > Acked-by: "Christian Brauner (Microsoft)" <brauner@xxxxxxxxxx> > > Link: https://lore.kernel.org/r/165962680944.3334508.6610023900349142034.stgit@xxxxxxxxxxxxxxxxxxxxxx/ # v1 > > Link: https://lore.kernel.org/r/165962729225.3357250.14350728846471527137.stgit@xxxxxxxxxxxxxxxxxxxxxx/ # v2 > > Link: https://lore.kernel.org/r/165970659095.2812394.6868894171102318796.stgit@xxxxxxxxxxxxxxxxxxxxxx/ # v3 > > Link: https://lore.kernel.org/r/166133579016.3678898.6283195019480567275.stgit@xxxxxxxxxxxxxxxxxxxxxx/ # v4 > > Link: https://lore.kernel.org/r/217595.1662033775@xxxxxxxxxxxxxxxxxxxxxx/ # v5 > > --- > > ver #7) > > - Drop lsm_set boolean > > - Link to v6: https://lore.kernel.org/r/20230802-master-v6-1-45d48299168b@xxxxxxxxxx > > > > ver #6) > > - Rebase onto v6.5.0-rc4 > > > > ver #5) > > - Removed unused variable. > > - Only allocate smack_mnt_opts if we're dealing with a submount. > > > > ver #4) > > - When doing a FOR_SUBMOUNT mount, don't set the root label in SELinux or > > Smack. > > > > ver #3) > > - Made LSM parameter extraction dependent on fc->purpose == > > FS_CONTEXT_FOR_SUBMOUNT. Shouldn't happen on FOR_RECONFIGURE. > > > > ver #2) > > - Added Smack support > > - Made LSM parameter extraction dependent on reference != NULL. > > --- > > fs/fs_context.c | 4 ++++ > > include/linux/lsm_hook_defs.h | 1 + > > include/linux/security.h | 6 +++++ > > security/security.c | 14 +++++++++++ > > security/selinux/hooks.c | 25 ++++++++++++++++++++ > > security/smack/smack_lsm.c | 54 +++++++++++++++++++++++++++++++++++++++++++ > > 6 files changed, 104 insertions(+) > > > > diff --git a/fs/fs_context.c b/fs/fs_context.c > > index 851214d1d013..a523aea956c4 100644 > > --- a/fs/fs_context.c > > +++ b/fs/fs_context.c > > @@ -282,6 +282,10 @@ static struct fs_context *alloc_fs_context(struct file_system_type *fs_type, > > break; > > } > > > > + ret = security_fs_context_init(fc, reference); > > + if (ret < 0) > > + goto err_fc; > > + > > /* TODO: Make all filesystems support this unconditionally */ > > init_fs_context = fc->fs_type->init_fs_context; > > if (!init_fs_context) > > diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h > > index 7308a1a7599b..7ce3550154b1 100644 > > --- 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_init, struct fs_context *fc, struct dentry *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 32828502f09e..61fda06fac9d 100644 > > --- 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_init(struct fs_context *fc, struct dentry *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_init(struct fs_context *fc, > > + struct dentry *reference) > > I think that's the wrong way of doing this hook. The security hook > really doesn't belong into alloc_fs_context(). > > I think what we want is a dedicated helper similar to vfs_dup_context(): > > // Only pass the superblock. There's no need for the dentry. I would > // avoid even passing fs_context but if that's preferred then sure. > security_fs_context_submount(struct fs_context *fc, const struct super_block *sb) > > vfs_submount_fs_context(struct file_system_type *fs_type, struct dentry *reference) > { > fc = fs_context_for_submount(fs_type, reference); > > security_fs_context_for_submount(fc, reference->d_sb); > } > > This automatically ensures it's only called for submounts, the LSM > doesn't need to care about fc->purpose and this isn't called > in a pure allocation function for all allocation calls. > > The we should switch all callers over to that new helper and unexport > that fs_context_for_submount() thing completely. Yes, that's more work > but that's the correct thing to do. And we need to audit fuse, cifs, > afs, and nfs anyway that they work fine with the new security hook.* > It's the same prototype. We could just move the hook call to the end of fs_context_for_submount, and that would be less churn for its callers. Or were you wanting to do that to make this a more gradual changeover for some reason? I will rework the security hook to take a sb pointer instead though. > > [1]: If really needed, then any additional fs specific work that needs > to be done during submount allocation should probably probably be > done in a new callback. > > struct fs_context_operations { > void (*free)(struct fs_context *fc); > int (*dup)(struct fs_context *fc, struct fs_context *src_fc); > + int (*submount)(struct fs_context *fc, const struct super_block *sb); -- Jeff Layton <jlayton@xxxxxxxxxx>