Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider: - [High] xfs: missing NULL check in xfs_dax_notify_failure() causes NULL pointer dereference - [High] dax: missing synchronize_srcu() in fs_put_dax() leads to Use-After-Free of xfs_mount --
commit b62dcd3b2d7873db8fcf1fc4a0c2b9c52417ad0a Author: Miklos Szeredi <[email protected]> dax: use READ_ONCE() in dax_holder() Make sure that a non-NULL check in callers remains valid even when racing with fs_put_dax(). > diff --git a/drivers/dax/super.c b/drivers/dax/super.c > index 824e1f6df3780..0a440f8b42e4f 100644 > --- a/drivers/dax/super.c > +++ b/drivers/dax/super.c > @@ -677,7 +677,7 @@ EXPORT_SYMBOL_GPL(put_dax); > */ > void *dax_holder(struct dax_device *dax_dev) > { > - return dax_dev->holder_data; > + return READ_ONCE(dax_dev->holder_data); [Severity: High] Does this code still leave a window for a NULL pointer dereference? The commit message mentions protecting a non-NULL check in callers, but the caller in xfs_dax_notify_failure() doesn't appear to have one: fs/xfs/xfs_notify_failure.c:xfs_dax_notify_failure() { struct xfs_mount *mp = dax_holder(dax_dev); if (!(mp->m_super->s_flags & SB_BORN)) { ... } If a concurrent unmount clears dax_dev->holder_data to NULL via fs_put_dax(), won't this result in assigning NULL to mp and immediately dereferencing mp->m_super? [Severity: High] Can a use-after-free occur on the returned xfs_mount pointer even if a NULL check is added? When a memory failure triggers dax_holder_notify_failure(), it acquires dax_read_lock() (which is SRCU) and calls xfs_dax_notify_failure(). Concurrently, if an unmount calls fs_put_dax(), it clears the holder data: drivers/dax/super.c:fs_put_dax() { ... WRITE_ONCE(dax_dev->holder_ops, NULL); prev = cmpxchg(&dax_dev->holder_data, holder, NULL); ... } Since fs_put_dax() returns without calling synchronize_srcu(&dax_srcu) to wait for active readers, the unmount process can proceed and destroy the xfs_mount structure. Won't the still-executing xfs_dax_notify_failure() then access the freed xfs_mount, resulting in a use-after-free? > } > EXPORT_SYMBOL_GPL(dax_holder); -- Sashiko AI review ยท https://sashiko.dev/#/patchset/[email protected]?part=2
