6.6-stable review patch. If anyone has any objections, please let me know.
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From: Rishabh Dave ridave@redhat.com
commit cda4672da1c26835dcbd7aec2bfed954eda9b5ef upstream.
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.
Cc: stable@vger.kernel.org Link: https://tracker.ceph.com/issues/59259 Signed-off-by: Rishabh Dave ridave@redhat.com Reviewed-by: Jeff Layton jlayton@kernel.org Reviewed-by: Xiubo Li xiubli@redhat.com Signed-off-by: Ilya Dryomov idryomov@gmail.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/ceph/caps.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
--- a/fs/ceph/caps.c +++ b/fs/ceph/caps.c @@ -1415,7 +1415,7 @@ static void __prep_cap(struct cap_msg_ar if (flushing & CEPH_CAP_XATTR_EXCL) { arg->old_xattr_buf = __ceph_build_xattrs_blob(ci); arg->xattr_version = ci->i_xattrs.version; - arg->xattr_buf = ci->i_xattrs.blob; + arg->xattr_buf = ceph_buffer_get(ci->i_xattrs.blob); } else { arg->xattr_buf = NULL; arg->old_xattr_buf = NULL; @@ -1513,6 +1513,7 @@ static void __send_cap(struct cap_msg_ar encode_cap_msg(msg, arg); ceph_con_send(&arg->session->s_con, msg); ceph_buffer_put(arg->old_xattr_buf); + ceph_buffer_put(arg->xattr_buf); if (arg->wake) wake_up_all(&ci->i_cap_wq); }