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: syzbot+6aaf7f48ae034ab0ea97@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=6aaf7f48ae034ab0ea97 Fixes: 382b1e8f30f7 ("kernfs: fix memory leak of kernfs_iattrs in __kernfs_new_node") Cc: stable@vger.kernel.org Signed-off-by: Will Rosenberg whrosenb@asu.edu ---
Notes: v1 -> v2: fix patch formatting issues v2 -> v3: add cc stable branch v3 -> v4: re-add the notes section.
This bug was introduced as part of a patch I made, fixing a memory leak in the error out case.
I apologize for the oversight. Further fuzzing revealed the bug, and after checking, I found that syzbot detected the same issue.
fs/kernfs/dir.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c index 5c0efd6b239f..29baeeb97871 100644 --- a/fs/kernfs/dir.c +++ b/fs/kernfs/dir.c @@ -681,8 +681,10 @@ static struct kernfs_node *__kernfs_new_node(struct kernfs_root *root, return kn;
err_out4: - simple_xattrs_free(&kn->iattr->xattrs, NULL); - kmem_cache_free(kernfs_iattrs_cache, kn->iattr); + 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));
base-commit: d358e5254674b70f34c847715ca509e46eb81e6f