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

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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: 382b1e8f30 ("kernfs: fix memory leak of kernfs_iattrs in __kernfs_new_node")
Signed-off-by: Will Rosenberg <whrosenb@asu.edu>
Link: https://patch.msgid.link/20251217060107.4171558-1-whrosenb@asu.edu
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Will Rosenberg
2025-12-16 23:01:07 -07:00
committed by Greg Kroah-Hartman
parent 87e7f60190
commit 2b74209458
1 changed files with 4 additions and 2 deletions
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6
fs/kernfs/dir.c
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@@ -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));