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Subject[PATCH v16 02/12] namei: allow nd_jump_link() to produce errors
Date
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 <viro@zeniv.linux.org.uk>
Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
---
fs/namei.c | 3 ++-
fs/proc/base.c | 5 +++--
fs/proc/namespaces.c | 17 ++++++++++++-----
include/linux/namei.h | 2 +-
security/apparmor/apparmorfs.c | 8 ++++++--
5 files changed, 24 insertions(+), 11 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index 671c3c1a3425..965a25b2e3df 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..fecd5b4af607 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -1626,8 +1626,9 @@ 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);
+ if (error)
+ path_put(&path);
out:
return ERR_PTR(error);
}
diff --git a/fs/proc/namespaces.c b/fs/proc/namespaces.c
index 08dd94df1a66..95e199fbad57 100644
--- a/fs/proc/namespaces.c
+++ b/fs/proc/namespaces.c
@@ -51,11 +51,18 @@ 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);
+ if (error)
+ path_put(&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..da045d0477a5 100644
--- a/security/apparmor/apparmorfs.c
+++ b/security/apparmor/apparmorfs.c
@@ -2455,16 +2455,20 @@ 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);
+ if (error)
+ path_put(&path);
aa_put_ns(ns);

- return NULL;
+ return ERR_PTR(error);
}

static int policy_readlink(struct dentry *dentry, char __user *buffer,
--
2.24.0
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