[PATCH v18 03/13] namei: allow nd_jump_link() to produce errors

[Aleksa Sarai]

In preparation for LOOKUP_NO_MAGICLINKS, it's necessary to add the
ability for nd_jump_link() to return an error which the corresponding
get_link() caller must propogate back up to the VFS.

Suggested-by: Al Viro <v...@zeniv.linux.org.uk>
Signed-off-by: Aleksa Sarai <cyp...@cyphar.com>
---
 fs/namei.c                     |  3 ++-
 fs/proc/base.c                 |  3 +--
 fs/proc/namespaces.c           | 14 +++++++++-----
 include/linux/namei.h          |  2 +-
 security/apparmor/apparmorfs.c |  6 ++++--
 5 files changed, 17 insertions(+), 11 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index 5a47d9c09581..1024a641f075 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -859,7 +859,7 @@ static int nd_jump_root(struct nameidata *nd)
  * Helper to directly jump to a known parsed path from ->get_link,
  * caller must have taken a reference to path beforehand.
  */
-void nd_jump_link(struct path *path)
+int nd_jump_link(struct path *path)
 {
        struct nameidata *nd = current->nameidata;
        path_put(&nd->path);
@@ -867,6 +867,7 @@ void nd_jump_link(struct path *path)
        nd->path = *path;
        nd->inode = nd->path.dentry->d_inode;
        nd->flags |= LOOKUP_JUMPED;
+       return 0;
 }
 
 static inline void put_link(struct nameidata *nd)
diff --git a/fs/proc/base.c b/fs/proc/base.c
index ebea9501afb8..ee97dd322f3e 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -1626,8 +1626,7 @@ static const char *proc_pid_get_link(struct dentry 
*dentry,
        if (error)
                goto out;
 
-       nd_jump_link(&path);
-       return NULL;
+       error = nd_jump_link(&path);
 out:
        return ERR_PTR(error);
 }
diff --git a/fs/proc/namespaces.c b/fs/proc/namespaces.c
index 08dd94df1a66..a8cca516f1a9 100644
--- a/fs/proc/namespaces.c
+++ b/fs/proc/namespaces.c
@@ -51,11 +51,15 @@ static const char *proc_ns_get_link(struct dentry *dentry,
        if (!task)
                return ERR_PTR(-EACCES);
 
-       if (ptrace_may_access(task, PTRACE_MODE_READ_FSCREDS)) {
-               error = ns_get_path(&ns_path, task, ns_ops);
-               if (!error)
-                       nd_jump_link(&ns_path);
-       }
+       if (!ptrace_may_access(task, PTRACE_MODE_READ_FSCREDS))
+               goto out;
+
+       error = ns_get_path(&ns_path, task, ns_ops);
+       if (error)
+               goto out;
+
+       error = nd_jump_link(&ns_path);
+out:
        put_task_struct(task);
        return ERR_PTR(error);
 }
diff --git a/include/linux/namei.h b/include/linux/namei.h
index 397a08ade6a2..758e9b47db6f 100644
--- a/include/linux/namei.h
+++ b/include/linux/namei.h
@@ -68,7 +68,7 @@ extern int follow_up(struct path *);
 extern struct dentry *lock_rename(struct dentry *, struct dentry *);
 extern void unlock_rename(struct dentry *, struct dentry *);
 
-extern void nd_jump_link(struct path *path);
+extern int __must_check nd_jump_link(struct path *path);
 
 static inline void nd_terminate_link(void *name, size_t len, size_t maxlen)
 {
diff --git a/security/apparmor/apparmorfs.c b/security/apparmor/apparmorfs.c
index 45d13b6462aa..0b7d6dce6291 100644
--- a/security/apparmor/apparmorfs.c
+++ b/security/apparmor/apparmorfs.c
@@ -2455,16 +2455,18 @@ static const char *policy_get_link(struct dentry 
*dentry,
 {
        struct aa_ns *ns;
        struct path path;
+       int error;
 
        if (!dentry)
                return ERR_PTR(-ECHILD);
+
        ns = aa_get_current_ns();
        path.mnt = mntget(aafs_mnt);
        path.dentry = dget(ns_dir(ns));
-       nd_jump_link(&path);
+       error = nd_jump_link(&path);
        aa_put_ns(ns);
 
-       return NULL;
+       return ERR_PTR(error);
 }
 
 static int policy_readlink(struct dentry *dentry, char __user *buffer,
-- 
2.24.0