CVE-2026-52944ksmbd: fix FSCTL permission bypass by adding a permission check for FSCTL_SET_SPARSE

Official description

In the Linux kernel, the following vulnerability has been resolved: ksmbd: fix FSCTL permission bypass by adding a permission check for FSCTL_SET_SPARSE FSCTL_SET_SPARSE in fsctl_set_sparse() modifies the file's sparse attribute and saves it through xattr without any permission checks. This exposes two issues: 1) A client on a read-only share can change the sparse attribute on files it opened, even though the share is read-only. Other FSCTL write operations already check test_tree_conn_flag(work->tcon, KSMBD_TREE_CONN_FLAG_WRITABLE), but FSCTL_SET_SPARSE does not. 2) Even on writable shares, clients without FILE_WRITE_DATA or FILE_WRITE_ATTRIBUTES access should not modify the sparse attribute. Similar handle-level checks exist in other functions but are missing here. Add both share-level writable check and per-handle access check. Use goto out on error to avoid leaking file references.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/ef664475c1bf1a27d45dae6848ca9c9c4d86853f
• https://git.kernel.org/stable/c/3a9a0a1c38ef90788f5d7c4b29903c8b220f744a
• https://git.kernel.org/stable/c/3127a884525dc8ca4def73254bfcd3ccef0bf812
• https://git.kernel.org/stable/c/c5ab11263e3c89aa7989afc5374ef7743e092fd0
• https://git.kernel.org/stable/c/de9eb0b44fa9123170e6245b49638e0e453c10f8
• https://git.kernel.org/stable/c/aef151bcfa494bfe983669de2726734b534adb73
• https://git.kernel.org/stable/c/cc57232cae23c0df91b4a59d0f519141ce9b5b02