CVE-2026-31444ksmbd: fix use-after-free and NULL deref in smb_grant_oplock()

Official description

In the Linux kernel, the following vulnerability has been resolved: ksmbd: fix use-after-free and NULL deref in smb_grant_oplock() smb_grant_oplock() has two issues in the oplock publication sequence: 1) opinfo is linked into ci->m_op_list (via opinfo_add) before add_lease_global_list() is called. If add_lease_global_list() fails (kmalloc returns NULL), the error path frees the opinfo via __free_opinfo() while it is still linked in ci->m_op_list. Concurrent m_op_list readers (opinfo_get_list, or direct iteration in smb_break_all_levII_oplock) dereference the freed node. 2) opinfo->o_fp is assigned after add_lease_global_list() publishes the opinfo on the global lease list. A concurrent find_same_lease_key() can walk the lease list and dereference opinfo->o_fp->f_ci while o_fp is still NULL. Fix by restructuring the publication sequence to eliminate post-publish failure: - Set opinfo->o_fp before any list publication (fixes NULL deref). - Preallocate lease_table via alloc_lease_table() before opinfo_add() so add_lease_global_list() becomes infallible after publication. - Keep the original m_op_list publication order (opinfo_add before lease list) so concurrent opens via same_client_has_lease() and opinfo_get_list() still see the in-flight grant. - Use opinfo_put() instead of __free_opinfo() on err_out so that the RCU-deferred free path is used. This also requires splitting add_lease_global_list() to take a preallocated lease_table and changing its return type from int to void, since it can no longer fail.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/9e785f004cbc56390479b77375726ea9b0d1a8a6
• https://git.kernel.org/stable/c/7de55bba69cbf0f9280daaea385daf08bc076121
• https://git.kernel.org/stable/c/a5c6f6d6ceefed2d5210ee420fb75f8362461f46
• https://git.kernel.org/stable/c/6d7e5a918c1d0aad06db0e17677b66fc9a471021
• https://git.kernel.org/stable/c/48623ec358c1c600fa1e38368746f933e0f1a617