Re: [PATCH] net: sunrpc: svcauth_gss: use BUG_ON instead of if condition followed by BUG

[J. Bruce Fields]

On Tue, Oct 24, 2017 at 02:18:52PM -0400, Jeff Layton wrote:
> On Tue, 2017-10-24 at 13:53 -0400, J. Bruce Fields wrote:
> > On Tue, Oct 24, 2017 at 01:26:49PM -0400, Weston Andros Adamson wrote:
> > > Is there a reason to BUG() in these places? Couldn't we WARN_ON_ONCE and 
> > > return an error?
> > 
> > I think the BUG() will just kill an nfsd thread that isn't holding any
> > interesting locks.
> > 
> 
> Not necessarily. If panic_on_oops is set (and it usually is in
> "production" setups), it'll crash the box there.

Maybe they're getting what they asked for?

> > The failures look unlikely.  (Except for that read_u32... return, I
> > wonder if we're missing a check there.)
> 
> Agreed, looks like you only hit an error if the read attempts to go out
> of bounds. In principle that shouldn't ever happen (and I haven't seen
> any reports of it).
> 
> Still...I agree with Dros that it's better to handle this without
> oopsing if we can. We can return an error from either of those
> functions. A sane error and a WARN_ONCE would be better here.

OK, OK, OK.

There are also some more BUGs that could use looking into if anyone
wants to.

--b.

commit eb754930662f
Author: J. Bruce Fields <bfie...@redhat.com>
Date:   Tue Oct 24 14:58:11 2017 -0400

    rpc: remove some BUG()s
    
    It would be kinder to WARN() and recover in several spots here instead
    of BUG()ing.
    
    Also, it looks like the read_u32_from_xdr_buf() call could actually
    fail, though it might require a broken (or malicious) client, so convert
    that to just an error return.
    
    Reported-by: Weston Andros Adamson <d...@monkey.org>
    Signed-off-by: J. Bruce Fields <bfie...@redhat.com>

diff --git a/net/sunrpc/auth_gss/svcauth_gss.c 
b/net/sunrpc/auth_gss/svcauth_gss.c
index 7b1ee5a0b03c..73165e9ca5bf 100644
--- a/net/sunrpc/auth_gss/svcauth_gss.c
+++ b/net/sunrpc/auth_gss/svcauth_gss.c
@@ -855,11 +855,13 @@ unwrap_integ_data(struct svc_rqst *rqstp, struct xdr_buf 
*buf, u32 seq, struct g
                return stat;
        if (integ_len > buf->len)
                return stat;
-       if (xdr_buf_subsegment(buf, &integ_buf, 0, integ_len))
-               BUG();
+       if (xdr_buf_subsegment(buf, &integ_buf, 0, integ_len)) {
+               WARN_ON_ONCE(1);
+               return stat;
+       }
        /* copy out mic... */
        if (read_u32_from_xdr_buf(buf, integ_len, &mic.len))
-               BUG();
+               return stat;
        if (mic.len > RPC_MAX_AUTH_SIZE)
                return stat;
        mic.data = kmalloc(mic.len, GFP_KERNEL);
@@ -1611,8 +1613,10 @@ svcauth_gss_wrap_resp_integ(struct svc_rqst *rqstp)
        BUG_ON(integ_len % 4);
        *p++ = htonl(integ_len);
        *p++ = htonl(gc->gc_seq);
-       if (xdr_buf_subsegment(resbuf, &integ_buf, integ_offset, integ_len))
-               BUG();
+       if (xdr_buf_subsegment(resbuf, &integ_buf, integ_offset, integ_len)) {
+               WARN_ON_ONCE(1);
+               goto out_err;
+       }
        if (resbuf->tail[0].iov_base == NULL) {
                if (resbuf->head[0].iov_len + RPC_MAX_AUTH_SIZE > PAGE_SIZE)
                        goto out_err;