Commit 2b742094 authored by Will Rosenberg's avatar Will Rosenberg Committed by Greg Kroah-Hartman
Browse files

fs/kernfs: null-ptr deref in simple_xattrs_free() 



There exists a null pointer dereference in simple_xattrs_free() as
part of the __kernfs_new_node() routine. Within __kernfs_new_node(),
err_out4 calls simple_xattr_free(), but kn->iattr may be NULL if
__kernfs_setattr() was never called. As a result, the first argument to
simple_xattrs_free() may be NULL + 0x38, and no NULL check is done
internally, causing an incorrect pointer dereference.

Add a check to ensure kn->iattr is not NULL, meaning __kernfs_setattr()
has been called and kn->iattr is allocated. Note that struct kernfs_node
kn is allocated with kmem_cache_zalloc, so we can assume kn->iattr will
be NULL if not allocated.

An alternative fix could be to not call simple_xattrs_free() at all. As
was previously discussed during the initial patch, simple_xattrs_free()
is not strictly needed and is included to be consistent with
kernfs_free_rcu(), which also helps the function maintain correctness if
changes are made in __kernfs_new_node().

Reported-by: default avatar <syzbot+6aaf7f48ae034ab0ea97@syzkaller.appspotmail.com>
Closes: https://syzkaller.appspot.com/bug?extid=6aaf7f48ae034ab0ea97


Fixes: 382b1e8f ("kernfs: fix memory leak of kernfs_iattrs in __kernfs_new_node")
Signed-off-by: default avatarWill Rosenberg <whrosenb@asu.edu>
Link: https://patch.msgid.link/20251217060107.4171558-1-whrosenb@asu.edu


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 87e7f601

fs/kernfs/dir.c

+4 −2
Original line number Diff line number Diff line
@@ -681,8 +681,10 @@ static struct kernfs_node *__kernfs_new_node(struct kernfs_root *root, 
	return kn;



 err_out4:

	if (kn->iattr) {

		simple_xattrs_free(&kn->iattr->xattrs, NULL);

		kmem_cache_free(kernfs_iattrs_cache, kn->iattr);

	}

 err_out3:

	spin_lock(&root->kernfs_idr_lock);

	idr_remove(&root->ino_idr, (u32)kernfs_ino(kn));