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>
