Re: linux-next: Tree for Jan 20 -- Kernel panic - Unable to mount root fs

On Wed, Jan 21, 2015 at 01:03:20PM -0800, Guenter Roeck wrote: > failing case: > > path_lookupat: calling path_init 'usr' flags=40 > path_init: link_path_walk() returned 0 > path_lookupat: path_init 'usr' flags=40[50] returned 0 > walk_component: lookup_fast() returned 1 > walk_component: lookup_slow() returned 0 > walk_component: inode= (null), negative=1 > do_path_lookup(usr, 0x10) > path_lookupat: calling path_init 'usr' flags=50 > path_init: link_path_walk() returned 0 > path_lookupat: path_init 'usr' flags=50[50] returned 0 > mkdir[c74012a0,/kkk] => 0 <==== SIC! Cute. 'k' being 0x6b, aka POISON_FREE... OK, the next question is what's been freed under us - I don't believe that it's dentry itself... Oh, fuck. OK, I see what happens. Look at kern_path_create(); it does LOOKUP_PARENT walk, leaving nd->last pointing to the last component of the *COPY* of the name it's just created, walked and freed. OK... Fortunately, struct nameidata is completely opaque outside of fs/namei.c, so we only need to care about a couple of codepaths. Folks, could you check if the following on top of linux-next fixes the problem?

diff --git a/fs/namei.c b/fs/namei.c index 323957f..cda89c3 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -2056,13 +2056,22 @@ static int do_path_lookup(int dfd, const char *name, /* does lookup, returns the object with parent locked */ struct dentry *kern_path_locked(const char *name, struct path *path) { + struct filename *filename = getname_kernel(name); struct nameidata nd; struct dentry *d; - int err = do_path_lookup(AT_FDCWD, name, LOOKUP_PARENT, &nd); - if (err) + int err; + + if (IS_ERR(filename)) + return ERR_CAST(filename); + + err = filename_lookup(AT_FDCWD, filename, LOOKUP_PARENT, &nd); + if (err) { + putname(filename); return ERR_PTR(err); + } if (nd.last_type != LAST_NORM) { path_put(&nd.path); + putname(filename); return ERR_PTR(-EINVAL); } mutex_lock_nested(&nd.path.dentry->d_inode->i_mutex, I_MUTEX_PARENT); @@ -2070,9 +2079,11 @@ struct dentry *kern_path_locked(const char *name, struct path *path) if (IS_ERR(d)) { mutex_unlock(&nd.path.dentry->d_inode->i_mutex); path_put(&nd.path); + putname(filename); return d; } *path = nd.path; + putname(filename); return d; } @@ -3314,7 +3325,7 @@ struct file *do_file_open_root(struct dentry *dentry, struct vfsmount *mnt, return file; } -struct dentry *kern_path_create(int dfd, const char *pathname, +static struct dentry *filename_create(int dfd, struct filename *name, struct path *path, unsigned int lookup_flags) { struct dentry *dentry = ERR_PTR(-EEXIST); @@ -3329,7 +3340,7 @@ struct dentry *kern_path_create(int dfd, const char *pathname, */ lookup_flags &= LOOKUP_REVAL; - error = do_path_lookup(dfd, pathname, LOOKUP_PARENT|lookup_flags, &nd); + error = filename_lookup(dfd, name, LOOKUP_PARENT|lookup_flags, &nd); if (error) return ERR_PTR(error); @@ -3383,6 +3394,19 @@ out: path_put(&nd.path); return dentry; } + +struct dentry *kern_path_create(int dfd, const char *pathname, + struct path *path, unsigned int lookup_flags) +{ + struct filename *filename = getname_kernel(pathname); + struct dentry *res = ERR_CAST(filename); + + if (!IS_ERR(filename)) { + res = filename_create(dfd, filename, path, lookup_flags); + putname(filename); + } + return res; +} EXPORT_SYMBOL(kern_path_create); void done_path_create(struct path *path, struct dentry *dentry) @@ -3401,7 +3425,7 @@ struct dentry *user_path_create(int dfd, const char __user *pathname, struct dentry *res; if (IS_ERR(tmp)) return ERR_CAST(tmp); - res = kern_path_create(dfd, tmp->name, path, lookup_flags); + res = filename_create(dfd, tmp, path, lookup_flags); putname(tmp); return res; }