CVE-2026-89788 is a vulnerability in Linux Kernel
Published on September 16, 2026
ksmbd: fix tree connection use-after-free in smb2_tree_connect()
In the Linux kernel, the following vulnerability has been resolved:
ksmbd: fix tree connection use-after-free in smb2_tree_connect()
ksmbd_tree_conn_connect() publishes a new tree connection in
sess->tree_conns with a single reference and returns its pointer to
smb2_tree_connect(). The handler continues to initialize the object and
build the response after publication. A concurrent session logoff can
erase the connection and drop that reference, freeing the object while
the handler still uses it.
BUG: KASAN: slab-use-after-free in smb2_tree_connect+0xe3d/0xf90
smb2_tree_connect (fs/smb/server/smb2pdu.c:2872)
handle_ksmbd_work
process_one_work
worker_thread
kthread
After xa_store() succeeds, take a second reference before releasing
tree_conns_lock. The original reference belongs to the xarray entry and
the second belongs to the creating smb2_tree_connect() handler.
Keep the references balanced in every path:
- On normal exit or an error after publication, smb2_tree_connect()
drops its creator reference. Error cleanup also calls
ksmbd_tree_conn_disconnect(), which drops the xarray reference only if
it removes the exact entry.
- SMB2 TREE_DISCONNECT uses the same helper to remove the entry and drop
its xarray reference. The request's existing lookup reference remains
owned by the request and is released by the existing cleanup.
- Session LOGOFF removes each entry and drops its xarray reference. If
it wins the race, later cleanup sees that the entry is gone and does
not drop that reference again.
To enforce this ownership, claim the disconnected state and erase the
exact entry atomically under tree_conns_lock. This guarantees one drop
for the xarray reference and one drop by each in-flight user, regardless
of which teardown path wins. If logoff removes the entry before
initialization completes, fail the connect instead of marking the
detached object TREE_CONNECTED.
Products Associated with CVE-2026-89788
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Affected Versions
Linux:- Version 33b235a6e6ebe0f05f3586a71e8d281d00f71e2e and below 4e30fbd26e84efa2e5cbec4eb11e126ac0c79313 is affected.
- Version 33b235a6e6ebe0f05f3586a71e8d281d00f71e2e and below b5ec6c462aab1062cf5d1e667ba7c6442f737055 is affected.
- Version dd45db4d9bbc8f122a9b4db5ce94ae29fcf03d3c is affected.
- Version 7b58ee8d0b91359554cf219cd4f33872ea2afd66 is affected.
- Version 5.15.145 and below 5.16 is affected.
- Version 6.1.71 and below 6.2 is affected.
- Version 6.6 is affected.
- Before 6.6 is unaffected.
- Version 7.2.6, <= 7.2.* is unaffected.
- Version 7.3-rc2, <= * is unaffected.