ksmbd: zero the FS_OBJECT_ID_INFORMATION buffer before filling it in

Overview

In the Linux kernel, the following vulnerability has been resolved:

ksmbd: zero the FS_OBJECT_ID_INFORMATION buffer before filling it in

smb2_get_info_filesystem() reports 64 bytes for FS_OBJECT_ID_INFORMATION, that is the whole of struct object_id_info, but writes only 46 of them:

• objid[] is 16 bytes, and when the volume UUID is not available only sizeof(stfs.f_fsid) (8) bytes are copied into it;
• extended_info.version_string[] is STRING_LENGTH (28) bytes, and only strlen("1.1.0") (5) bytes are copied into it.

The response buffer is zeroed on allocation (kvzalloc() in smb2_allocate_rsp_buf()), so for a standalone request the remaining 31 bytes are zero. In a compound request they need not be. The offset of the next response is advanced by the length pinned for the previous one, so if a preceding command wrote its reply into the buffer and then failed, smb2_set_err_rsp() pins only the short error response and the next reply lands inside the area that has already been written. Only the header is cleared there:

memset((char *)rsp_hdr, 0, sizeof(struct smb2_hdr) + 2);

The client then receives up to 31 bytes of a response it was not meant to see, including one that failed with an access denied error.

Clear the structure before filling it in. As a side effect version_string is now NUL terminated.

Affected

• Linux >= e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 < dbd0f13de153d7094b85034daffa7533d7c2b17a
• Linux >= e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 < 90898571fb2c6813c007a62833dd65c00481d44e
• Linux >= e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 < 1a35a81c302b36fe4acd35b47b51d5d73e89ba0a
• Linux >= e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 < 3fc33ac2125b60f103592b83821f69f3f9aa23ba
• Linux >= e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 < 898cb4f2e12a5ddea1b2d821cc642c3100f46da7
• Linux >= e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 < 015fffa48e96ca8d73a627445341ccff86b02251
• Linux >= e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 < 399aa12450a61a5c73dc77e73f069ece9687c95d
• Linux 5.15

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.