Commit 0766ec82 authored by Stephen Brennan's avatar Stephen Brennan Committed by Al Viro
Browse files

namei: Fix use after free in kern_path_locked 

In 0ee50b47 ("namei: change filename_parentat() calling
conventions"), filename_parentat() was made to always call putname() on
the  filename before returning, and kern_path_locked() was migrated to
this calling convention.  However, kern_path_locked() uses the "last"
parameter to lookup and potentially create a new dentry. The last
parameter contains the last component of the path and points within the
filename, which was recently freed at the end of filename_parentat().
Thus, when kern_path_locked() calls __lookup_hash(), it is using the
filename after it has already been freed.

In other words, these calling conventions had been wrong for the
only remaining caller of filename_parentat().  Everything else
is using __filename_parentat(), which does not drop the reference;
so should kern_path_locked().

Switch kern_path_locked() to use of __filename_parentat() and move
getting/dropping struct filename into wrapper.  Remove filename_parentat(),
now that we have no remaining callers.

Fixes: 0ee50b47 ("namei: change filename_parentat() calling conventions")
Link: https://lore.kernel.org/linux-fsdevel/YS9D4AlEsaCxLFV0@infradead.org/
Link: https://lore.kernel.org/linux-fsdevel/YS+csMTV2tTXKg3s@zeniv-ca.linux.org.uk/


Cc: Christoph Hellwig <hch@infradead.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Reported-by: default avatar <syzbot+fb0d60a179096e8c2731@syzkaller.appspotmail.com>
Signed-off-by: default avatarStephen Brennan <stephen.s.brennan@oracle.com>
Co-authored-by: default avatarDmitry Kadashev <dkadashev@gmail.com>
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent 4b93c544

fs/namei.c

+14 −15
Original line number Diff line number Diff line
@@ -2514,6 +2514,7 @@ static int path_parentat(struct nameidata *nd, unsigned flags, 
	return err;

}



/* Note: this does not consume "name" */

static int __filename_parentat(int dfd, struct filename *name,

			     unsigned int flags, struct path *parent,

			     struct qstr *last, int *type)
@@ -2538,25 +2539,14 @@ static int __filename_parentat(int dfd, struct filename *name, 
	return retval;

}



static int filename_parentat(int dfd, struct filename *name,

				unsigned int flags, struct path *parent,

				struct qstr *last, int *type)

{

	int retval = __filename_parentat(dfd, name, flags, parent, last, type);



	putname(name);

	return retval;

}



/* does lookup, returns the object with parent locked */

struct dentry *kern_path_locked(const char *name, struct path *path)

static struct dentry *__kern_path_locked(struct filename *name, struct path *path)

{

	struct dentry *d;

	struct qstr last;

	int type, error;



	error = filename_parentat(AT_FDCWD, getname_kernel(name), 0, path,

				    &last, &type);

	error = __filename_parentat(AT_FDCWD, name, 0, path, &last, &type);

	if (error)

		return ERR_PTR(error);

	if (unlikely(type != LAST_NORM)) {
@@ -2572,6 +2562,15 @@ struct dentry *kern_path_locked(const char *name, struct path *path) 
	return d;

}



struct dentry *kern_path_locked(const char *name, struct path *path)

{

	struct filename *filename = getname_kernel(name);

	struct dentry *res = __kern_path_locked(filename, path);



	putname(filename);

	return res;

}



int kern_path(const char *name, unsigned int flags, struct path *path)

{

	return filename_lookup(AT_FDCWD, getname_kernel(name),