In the Linux kernel, the following vulnerability has been resolved:
smb: client: avoid using uninitialized SIDs in cifs_posix_to_fattr()
cifs_posix_to_fattr() ignores the return value of posix_info_parse().
When a malformed POSIX directory entry is encountered (e.g. invalid
SID lengths from an untrusted server), posix_info_parse() returns -1
without populating the ‘parsed’ struct. The uninitialized stack
memory in parsed.owner and parsed.group is then passed to
sid_to_id(), which processes the garbage bytes and passes them to
request_key() to construct a SID string, potentially leaking kernel
stack contents to the userspace idmap daemon.
Fix this by checking the return value and skipping the SID-to-id
mapping when parsing fails. The remaining fattr fields (timestamps,
mode, etc.) are populated directly from the ‘info’ pointer so they
are unaffected.
