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

Al Viro
2015-01-21T03:36:00Z

On Tue, Jan 20, 2015 at 06:44:34PM -0800, Guenter Roeck wrote:
> >The shit hits the fan earlier - when we end up missing /dev. There are
> >two places where it could've been created (depending on CONFIG_BLK_DEV_INITRD);
> > sys_mkdir(collected, mode);
> >in init/initramfs.c (line 353 in linux-next) and
> > err = sys_mkdir((const char __user __force *) "/dev", 0755);
> >in init/noinitramfs.c (line 32). The latter would've screamed on failure;
> >could you printk of collected (%s), mode (%o) and return value (%d) in the
> >former and see what happens?
> >
>
> sys_mkdir .:40775 returned -17
> sys_mkdir usr:40775 returned 0
> sys_mkdir usr/lib:40775 returned -2
> sys_mkdir usr/share:40755 returned -2
> sys_mkdir usr/share/udhcpc:40755 returned -2
> sys_mkdir usr/bin:40775 returned -2
> sys_mkdir usr/sbin:40775 returned -2
> sys_mkdir mnt:40775 returned 0
> sys_mkdir proc:40775 returned 0
> sys_mkdir root:40775 returned 0
> sys_mkdir lib:40775 returned 0
> sys_mkdir lib/modules:40775 returned -2
> sys_mkdir lib/modules/3.9.2:40775 returned -2
> sys_mkdir lib/modules/3.9.2/kernel:40775 returned -2
>
> with
> int err = sys_mkdir(collected, mode);
> pr_info("sys_mkdir %s:%o returned %d\n", collected, mode, err);
> added in init/initramfs.c.

Just what is lib/modules/3.9.2 doing there? In any case, I think I have at
least a plausible direction for digging. Look:

struct dentry *user_path_create(int dfd, const char __user *pathname,
struct path *path, unsigned int lookup_flags)
{
struct filename *tmp = getname(pathname);
struct dentry *res;
if (IS_ERR(tmp))
return ERR_CAST(tmp);
res = kern_path_create(dfd, tmp->name, path, lookup_flags);

struct dentry *kern_path_create(int dfd, const char *pathname,
struct path *path, unsigned int lookup_flags)
{
struct dentry *dentry = ERR_PTR(-EEXIST);
struct nameidata nd;
int err2;
int error;
bool is_dir = (lookup_flags & LOOKUP_DIRECTORY);

/*
* Note that only LOOKUP_REVAL and LOOKUP_DIRECTORY matter here. Any
* other flags passed in are ignored!
*/
lookup_flags &= LOOKUP_REVAL;

error = do_path_lookup(dfd, pathname, LOOKUP_PARENT|lookup_flags, &nd);

static int do_path_lookup(int dfd, const char *name,
unsigned int flags, struct nameidata *nd)
{
int retval;
struct filename *filename;

filename = getname_kernel(name);
if (unlikely(IS_ERR(filename)))
return PTR_ERR(filename);
retval = filename_lookup(dfd, filename, flags, nd);

and we have done getname_kernel() on the name->name of result of getname().
At the very least, it's pointless - we already *have* struct filename for
that sucker. Now, it shouldn't have screwed the things up - it would better
not, anyway, since we might legitimately have two identical pathname
among the syscall arguments. However, let's see if this (on top of
linux-next, in addition to the same printks) changes behaviour:

diff --git a/fs/namei.c b/fs/namei.c
index 323957f..c7d107c 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -3314,7 +3314,7 @@ 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 *__kern_path_create(int dfd, struct filename *name,
struct path *path, unsigned int lookup_flags)
{
struct dentry *dentry = ERR_PTR(-EEXIST);
@@ -3329,7 +3329,7 @@ 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 +3383,19 @@ 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 = __kern_path_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 +3414,7 @@ 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 = __kern_path_create(dfd, tmp, path, lookup_flags);
putname(tmp);
return res;
}