CVE-2026-99115

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

ksmbd: fill in FileSysIdentifier in FS POSIX INFORMATION

smb2 get info filesystem() reports 56 bytes for FS POSIX INFORMATION, that is the whole of FILE SYSTEM POSIX INFO, but never assigns FileSysIdentifier. Those eight bytes go to the client as they are found in the response buffer.

The buffer is zeroed on allocation, so a standalone request leaks nothing. A compound request can leak: the offset of the next response is advanced by the length pinned for the previous one, so a reply that was written into the buffer and then dropped in favour of the short error response of smb2 set err rsp() stays there, and the next reply is laid over it with only the header cleared.

Report the file system id statfs() returned, which is what the field is for. FileSysIdentifier is le64 and f fsid is a pair of ints, so assemble the value first, val[0] as the low half, and convert it on the way out.