On Mon, 2022-11-28 at 12:12 -0500, Jeff Layton wrote:
> On Sun, 2022-11-27 at 12:17 -0500, Chuck Lever wrote:
> > If a zero length is passed to kmalloc() it returns 0x10, which is
> > not a valid address. gss_verify_mic() subsequently crashes when it
> > attempts to dereference that pointer.
> >
> > Instead of allocating this memory on every call based on an
> > untrusted size value, use a piece of dynamically-allocated scratch
> > memory that is always available.
> >
> > Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
> > ---
> > net/sunrpc/auth_gss/svcauth_gss.c | 55 ++++++++++++++++++++++---------------
> > 1 file changed, 32 insertions(+), 23 deletions(-)
> >
> > diff --git a/net/sunrpc/auth_gss/svcauth_gss.c b/net/sunrpc/auth_gss/svcauth_gss.c
> > index 9a5db285d4ae..148bb0a7fa5b 100644
> > --- a/net/sunrpc/auth_gss/svcauth_gss.c
> > +++ b/net/sunrpc/auth_gss/svcauth_gss.c
> > @@ -49,11 +49,36 @@
> > #include <linux/sunrpc/svcauth.h>
> > #include <linux/sunrpc/svcauth_gss.h>
> > #include <linux/sunrpc/cache.h>
> > +#include <linux/sunrpc/gss_krb5.h>
> >
> > #include <trace/events/rpcgss.h>
> >
> > #include "gss_rpc_upcall.h"
> >
> > +/*
> > + * Unfortunately there isn't a maximum checksum size exported via the
> > + * GSS API. Manufacture one based on GSS mechanisms supported by this
> > + * implementation.
> > + */
> > +#define GSS_MAX_CKSUMSIZE (GSS_KRB5_TOK_HDR_LEN + GSS_KRB5_MAX_CKSUM_LEN)
> > +
> > +/*
> > + * This value may be increased in the future to accommodate other
> > + * usage of the scratch buffer.
> > + */
> > +#define GSS_SCRATCH_SIZE GSS_MAX_CKSUMSIZE
> > +
> > +struct gss_svc_data {
> > + /* decoded gss client cred: */
> > + struct rpc_gss_wire_cred clcred;
> > + /* save a pointer to the beginning of the encoded verifier,
> > + * for use in encryption/checksumming in svcauth_gss_release: */
> > + __be32 *verf_start;
> > + struct rsc *rsci;
> > +
> > + /* for temporary results */
> > + u8 gsd_scratch[GSS_SCRATCH_SIZE];
> > +};
> >
> > /* The rpcsec_init cache is used for mapping RPCSEC_GSS_{,CONT_}INIT requests
> > * into replies.
> > @@ -887,13 +912,11 @@ read_u32_from_xdr_buf(struct xdr_buf *buf, int base, u32 *obj)
> > static int
> > unwrap_integ_data(struct svc_rqst *rqstp, struct xdr_buf *buf, u32 seq, struct gss_ctx *ctx)
> > {
> > + struct gss_svc_data *gsd = rqstp->rq_auth_data;
> > u32 integ_len, rseqno, maj_stat;
> > - int stat = -EINVAL;
> > struct xdr_netobj mic;
> > struct xdr_buf integ_buf;
> >
> > - mic.data = NULL;
> > -
> > /* NFS READ normally uses splice to send data in-place. However
> > * the data in cache can change after the reply's MIC is computed
> > * but before the RPC reply is sent. To prevent the client from
> > @@ -917,11 +940,9 @@ unwrap_integ_data(struct svc_rqst *rqstp, struct xdr_buf *buf, u32 seq, struct g
> > /* copy out mic... */
> > if (read_u32_from_xdr_buf(buf, integ_len, &mic.len))
> > goto unwrap_failed;
> > - if (mic.len > RPC_MAX_AUTH_SIZE)
> > - goto unwrap_failed;
> > - mic.data = kmalloc(mic.len, GFP_KERNEL);
> > - if (!mic.data)
> > + if (mic.len > sizeof(gsd->gsd_scratch))
> > goto unwrap_failed;
> > + mic.data = gsd->gsd_scratch;
> > if (read_bytes_from_xdr_buf(buf, integ_len + 4, mic.data, mic.len))
> > goto unwrap_failed;
> > maj_stat = gss_verify_mic(ctx, &integ_buf, &mic);
> > @@ -932,20 +953,17 @@ unwrap_integ_data(struct svc_rqst *rqstp, struct xdr_buf *buf, u32 seq, struct g
> > goto bad_seqno;
> > /* trim off the mic and padding at the end before returning */
> > xdr_buf_trim(buf, round_up_to_quad(mic.len) + 4);
> > - stat = 0;
> > -out:
> > - kfree(mic.data);
> > - return stat;
> > + return 0;
> >
> > unwrap_failed:
> > trace_rpcgss_svc_unwrap_failed(rqstp);
> > - goto out;
> > + return -EINVAL;
> > bad_seqno:
> > trace_rpcgss_svc_seqno_bad(rqstp, seq, rseqno);
> > - goto out;
> > + return -EINVAL;
> > bad_mic:
> > trace_rpcgss_svc_mic(rqstp, maj_stat);
> > - goto out;
> > + return -EINVAL;
> > }
> >
> > static inline int
> > @@ -1023,15 +1041,6 @@ unwrap_priv_data(struct svc_rqst *rqstp, struct xdr_buf *buf, u32 seq, struct gs
> > return -EINVAL;
> > }
> >
> > -struct gss_svc_data {
> > - /* decoded gss client cred: */
> > - struct rpc_gss_wire_cred clcred;
> > - /* save a pointer to the beginning of the encoded verifier,
> > - * for use in encryption/checksumming in svcauth_gss_release: */
> > - __be32 *verf_start;
> > - struct rsc *rsci;
> > -};
> > -
> > static int
> > svcauth_gss_set_client(struct svc_rqst *rqstp)
> > {
> >
> >
>
> That makes a lot more sense!
>
> Reviewed-by: Jeff Layton <jlayton@xxxxxxxxxx>
How did you find this, btw? Is there a bug report or something?
--
Jeff Layton <jlayton@xxxxxxxxxx>
