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;