CVE-2026-52944

Summary

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 Software

VendorProductVersion RangeStatus
LinuxLinuxe2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 < ef664475c1bf1a27d45dae6848ca9c9c4d86853faffected
LinuxLinuxe2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 < 3a9a0a1c38ef90788f5d7c4b29903c8b220f744aaffected
LinuxLinuxe2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 < 3127a884525dc8ca4def73254bfcd3ccef0bf812affected
LinuxLinuxe2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 < c5ab11263e3c89aa7989afc5374ef7743e092fd0affected
LinuxLinuxe2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 < de9eb0b44fa9123170e6245b49638e0e453c10f8affected
LinuxLinuxe2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 < aef151bcfa494bfe983669de2726734b534adb73affected
LinuxLinuxe2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 < cc57232cae23c0df91b4a59d0f519141ce9b5b02affected
LinuxLinux5.15affected
LinuxLinux0 < 5.15unaffected
LinuxLinux5.15.221 <= 5.15.*unaffected
LinuxLinux6.1.188 <= 6.1.*unaffected
LinuxLinux6.6.143 <= 6.6.*unaffected
LinuxLinux6.12.110 <= 6.12.*unaffected
LinuxLinux6.18.35 <= 6.18.*unaffected
LinuxLinux7.0.12 <= 7.0.*unaffected
LinuxLinux7.1 <= *unaffected

Weaknesses

References