> On Nov 28, 2022, at 12:13 PM, Jeff Layton <jlayton@xxxxxxxxxx> wrote:
>
> 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?
I recently fixed the same problem on the client-side. I managed
to trigger the client-side problem while working on the server
GSS overhaul.
--
Chuck Lever
