CVE-2024-26689

In the Linux kernel, the following vulnerability has been resolved: ceph:
prevent use-after-free in encode_cap_msg() In fs/ceph/caps.c, in
encode_cap_msg(), “use after free” error was caught by KASAN at this line -
‘ceph_buffer_get(arg->xattr_buf);’. This implies before the refcount could
be increment here, it was freed. In same file, in “handle_cap_grant()”
refcount is decremented by this line -
‘ceph_buffer_put(ci->i_xattrs.blob);’. It appears that a race occurred and
resource was freed by the latter line before the former line could
increment it. encode_cap_msg() is called by __send_cap() and __send_cap()
is called by ceph_check_caps() after calling __prep_cap(). __prep_cap() is
where arg->xattr_buf is assigned to ci->i_xattrs.blob. This is the spot
where the refcount must be increased to prevent “use after free” error.