[RFC PATCH ghak100 V1 1/2] audit: avoid fcaps on MNT_FORCE

[Richard Guy Briggs]

Don't fetch fcaps when umount2 is called with MNT_FORCE to avoid a
process hang while it waits for the missing resource to (possibly never)
re-appear.

Note the comment above user_path_mountpoint_at():
 * A umount is a special case for path walking. We're not actually interested
 * in the inode in this situation, and ESTALE errors can be a problem.  We
 * simply want track down the dentry and vfsmount attached at the mountpoint
 * and avoid revalidating the last component.

This can happen on ceph, cifs, 9p, lustre, fuse (gluster) or NFS.

Please see the github issue tracker
https://github.com/linux-audit/audit-kernel/issues/100

Signed-off-by: Richard Guy Briggs <rgb@xxxxxxxxxx>
---
 fs/namei.c            | 2 +-
 fs/namespace.c        | 3 +++
 include/linux/audit.h | 8 ++++++--
 kernel/audit.c        | 5 +++--
 kernel/audit.h        | 2 +-
 kernel/auditsc.c      | 6 +++---
 6 files changed, 17 insertions(+), 9 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index 0cab6494978c..5ac8410b704c 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2720,7 +2720,7 @@ int user_path_at_empty(int dfd, const char __user *name, unsigned flags,
 	if (unlikely(error == -ESTALE))
 		error = path_mountpoint(&nd, flags | LOOKUP_REVAL, path);
 	if (likely(!error))
-		audit_inode(name, path->dentry, 0);
+		audit_inode(name, path->dentry, flags & LOOKUP_NO_REVAL);
 	restore_nameidata();
 	putname(name);
 	return error;
diff --git a/fs/namespace.c b/fs/namespace.c
index 99186556f8d3..5bae5bbd4e1f 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1636,6 +1636,9 @@ int ksys_umount(char __user *name, int flags)
 	if (!(flags & UMOUNT_NOFOLLOW))
 		lookup_flags |= LOOKUP_FOLLOW;
 
+	if (!(flags & MNT_FORCE))
+		lookup_flags |= LOOKUP_NO_REVAL;
+
 	retval = user_path_mountpoint_at(AT_FDCWD, name, lookup_flags, &path);
 	if (retval)
 		goto out;
diff --git a/include/linux/audit.h b/include/linux/audit.h
index 9334fbef7bae..503f1710c9d0 100644
--- a/include/linux/audit.h
+++ b/include/linux/audit.h
@@ -25,6 +25,7 @@
 
 #include <linux/sched.h>
 #include <linux/ptrace.h>
+#include <linux/namei.h>  /* LOOKUP_* */
 #include <uapi/linux/audit.h>
 
 #define AUDIT_INO_UNSET ((unsigned long)-1)
@@ -229,6 +230,7 @@ extern void __audit_syscall_entry(int major, unsigned long a0, unsigned long a1,
 
 #define AUDIT_INODE_PARENT	1	/* dentry represents the parent */
 #define AUDIT_INODE_HIDDEN	2	/* audit record should be hidden */
+#define AUDIT_INODE_NOREVAL	4	/* audit record incomplete */
 extern void __audit_inode(struct filename *name, const struct dentry *dentry,
 				unsigned int flags);
 extern void __audit_file(const struct file *);
@@ -289,11 +291,13 @@ static inline void audit_getname(struct filename *name)
 }
 static inline void audit_inode(struct filename *name,
 				const struct dentry *dentry,
-				unsigned int parent) {
+				unsigned int lflags) {
 	if (unlikely(!audit_dummy_context())) {
 		unsigned int flags = 0;
-		if (parent)
+		if (lflags & LOOKUP_PARENT)
 			flags |= AUDIT_INODE_PARENT;
+		if (lflags & LOOKUP_NO_REVAL)
+			flags |= AUDIT_INODE_NOREVAL;
 		__audit_inode(name, dentry, flags);
 	}
 }
diff --git a/kernel/audit.c b/kernel/audit.c
index 2a8058764aa6..45ca6d15ce89 100644
--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -2097,7 +2097,7 @@ static inline int audit_copy_fcaps(struct audit_names *name,
 
 /* Copy inode data into an audit_names. */
 void audit_copy_inode(struct audit_names *name, const struct dentry *dentry,
-		      struct inode *inode)
+		      struct inode *inode, unsigned int flags)
 {
 	name->ino   = inode->i_ino;
 	name->dev   = inode->i_sb->s_dev;
@@ -2106,7 +2106,8 @@ void audit_copy_inode(struct audit_names *name, const struct dentry *dentry,
 	name->gid   = inode->i_gid;
 	name->rdev  = inode->i_rdev;
 	security_inode_getsecid(inode, &name->osid);
-	audit_copy_fcaps(name, dentry);
+	if (!(flags & AUDIT_INODE_NOREVAL))
+		audit_copy_fcaps(name, dentry);
 }
 
 /**
diff --git a/kernel/audit.h b/kernel/audit.h
index 214e14948370..7db09151c2d0 100644
--- a/kernel/audit.h
+++ b/kernel/audit.h
@@ -212,7 +212,7 @@ struct audit_context {
 
 extern void audit_copy_inode(struct audit_names *name,
 			     const struct dentry *dentry,
-			     struct inode *inode);
+			     struct inode *inode, unsigned int flags);
 extern void audit_log_cap(struct audit_buffer *ab, char *prefix,
 			  kernel_cap_t *cap);
 extern void audit_log_name(struct audit_context *context,
diff --git a/kernel/auditsc.c b/kernel/auditsc.c
index b2d1f043f17f..d39a7fbaf944 100644
--- a/kernel/auditsc.c
+++ b/kernel/auditsc.c
@@ -1846,7 +1846,7 @@ void __audit_inode(struct filename *name, const struct dentry *dentry,
 		n->type = AUDIT_TYPE_NORMAL;
 	}
 	handle_path(dentry);
-	audit_copy_inode(n, dentry, inode);
+	audit_copy_inode(n, dentry, inode, flags & AUDIT_INODE_NOREVAL);
 }
 
 void __audit_file(const struct file *file)
@@ -1947,7 +1947,7 @@ void __audit_inode_child(struct inode *parent,
 		n = audit_alloc_name(context, AUDIT_TYPE_PARENT);
 		if (!n)
 			return;
-		audit_copy_inode(n, NULL, parent);
+		audit_copy_inode(n, NULL, parent, 0);
 	}
 
 	if (!found_child) {
@@ -1966,7 +1966,7 @@ void __audit_inode_child(struct inode *parent,
 	}
 
 	if (inode)
-		audit_copy_inode(found_child, dentry, inode);
+		audit_copy_inode(found_child, dentry, inode, 0);
 	else
 		found_child->ino = AUDIT_INO_UNSET;
 }
-- 
1.8.3.1