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Subject[PATCH v16 03/12] namei: allow set_root() to produce errors
Date
For LOOKUP_BENEATH and LOOKUP_IN_ROOT it is necessary to ensure that
set_root() is never called, and thus (for hardening purposes) it should
return an error rather than permit a breakout from the root. In
addition, move all of the repetitive set_root() calls to nd_jump_root().

Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
---
fs/namei.c | 35 ++++++++++++++++++++++++-----------
1 file changed, 24 insertions(+), 11 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index 965a25b2e3df..259652667881 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -798,7 +798,7 @@ static int complete_walk(struct nameidata *nd)
return status;
}

-static void set_root(struct nameidata *nd)
+static int set_root(struct nameidata *nd)
{
struct fs_struct *fs = current->fs;

@@ -814,6 +814,7 @@ static void set_root(struct nameidata *nd)
get_fs_root(fs, &nd->root);
nd->flags |= LOOKUP_ROOT_GRABBED;
}
+ return 0;
}

static void path_put_conditional(struct path *path, struct nameidata *nd)
@@ -837,6 +838,11 @@ static inline void path_to_nameidata(const struct path *path,

static int nd_jump_root(struct nameidata *nd)
{
+ if (!nd->root.mnt) {
+ int error = set_root(nd);
+ if (error)
+ return error;
+ }
if (nd->flags & LOOKUP_RCU) {
struct dentry *d;
nd->path = nd->root;
@@ -1080,10 +1086,9 @@ const char *get_link(struct nameidata *nd)
return res;
}
if (*res == '/') {
- if (!nd->root.mnt)
- set_root(nd);
- if (unlikely(nd_jump_root(nd)))
- return ERR_PTR(-ECHILD);
+ error = nd_jump_root(nd);
+ if (unlikely(error))
+ return ERR_PTR(error);
while (unlikely(*++res == '/'))
;
}
@@ -1698,8 +1703,13 @@ static inline int may_lookup(struct nameidata *nd)
static inline int handle_dots(struct nameidata *nd, int type)
{
if (type == LAST_DOTDOT) {
- if (!nd->root.mnt)
- set_root(nd);
+ int error = 0;
+
+ if (!nd->root.mnt) {
+ error = set_root(nd);
+ if (error)
+ return error;
+ }
if (nd->flags & LOOKUP_RCU) {
return follow_dotdot_rcu(nd);
} else
@@ -2162,6 +2172,7 @@ static int link_path_walk(const char *name, struct nameidata *nd)
/* must be paired with terminate_walk() */
static const char *path_init(struct nameidata *nd, unsigned flags)
{
+ int error;
const char *s = nd->name->name;

if (!*s)
@@ -2194,11 +2205,13 @@ static const char *path_init(struct nameidata *nd, unsigned flags)
nd->path.dentry = NULL;

nd->m_seq = read_seqbegin(&mount_lock);
+
+ /* Figure out the starting path and root (if needed). */
if (*s == '/') {
- set_root(nd);
- if (likely(!nd_jump_root(nd)))
- return s;
- return ERR_PTR(-ECHILD);
+ error = nd_jump_root(nd);
+ if (unlikely(error))
+ return ERR_PTR(error);
+ return s;
} else if (nd->dfd == AT_FDCWD) {
if (flags & LOOKUP_RCU) {
struct fs_struct *fs = current->fs;
--
2.24.0
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