Backport of upstream fixes to NFSD's duplicate reply cache. These
have been hand-applied and tested with the same reproducer as was
used to create the upstream fixes.
---
Chuck Lever (2):
NFSD: Fix "start of NFS reply" pointer passed to nfsd_cache_update()
NFSD: Fix checksum mismatches in the duplicate reply cache
fs/nfsd/cache.h | 4 +--
fs/nfsd/nfscache.c | 64 +++++++++++++++++++++++++++++++---------------
fs/nfsd/nfssvc.c | 14 ++++++++--
3 files changed, 57 insertions(+), 25 deletions(-)
--
Chuck Lever
From: Chuck Lever <[email protected]>
[ Upstream commit 1caf5f61dd8430ae5a0b4538afe4953ce7517cbb ]
The "statp + 1" pointer that is passed to nfsd_cache_update() is
supposed to point to the start of the egress NFS Reply header. In
fact, it does point there for AUTH_SYS and RPCSEC_GSS_KRB5 requests.
But both krb5i and krb5p add fields between the RPC header's
accept_stat field and the start of the NFS Reply header. In those
cases, "statp + 1" points at the extra fields instead of the Reply.
The result is that nfsd_cache_update() caches what looks to the
client like garbage.
A connection break can occur for a number of reasons, but the most
common reason when using krb5i/p is a GSS sequence number window
underrun. When an underrun is detected, the server is obliged to
drop the RPC and the connection to force a retransmit with a fresh
GSS sequence number. The client presents the same XID, it hits in
the server's DRC, and the server returns the garbage cache entry.
The "statp + 1" argument has been used since the oldest changeset
in the kernel history repo, so it has been in nfsd_dispatch()
literally since before history began. The problem arose only when
the server-side GSS implementation was added twenty years ago.
Reviewed-by: Jeff Layton <[email protected]>
Tested-by: Jeff Layton <[email protected]>
Signed-off-by: Chuck Lever <[email protected]>
---
fs/nfsd/nfssvc.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/fs/nfsd/nfssvc.c b/fs/nfsd/nfssvc.c
index c7af1095f6b5..378ec82bd390 100644
--- a/fs/nfsd/nfssvc.c
+++ b/fs/nfsd/nfssvc.c
@@ -988,6 +988,7 @@ int nfsd_dispatch(struct svc_rqst *rqstp)
const struct svc_procedure *proc = rqstp->rq_procinfo;
__be32 *statp = rqstp->rq_accept_statp;
struct nfsd_cacherep *rp;
+ __be32 *nfs_reply;
/*
* Give the xdr decoder a chance to change this if it wants
@@ -1008,6 +1009,7 @@ int nfsd_dispatch(struct svc_rqst *rqstp)
goto out_dropit;
}
+ nfs_reply = xdr_inline_decode(&rqstp->rq_res_stream, 0);
*statp = proc->pc_func(rqstp);
if (test_bit(RQ_DROPME, &rqstp->rq_flags))
goto out_update_drop;
@@ -1015,7 +1017,7 @@ int nfsd_dispatch(struct svc_rqst *rqstp)
if (!proc->pc_encode(rqstp, &rqstp->rq_res_stream))
goto out_encode_err;
- nfsd_cache_update(rqstp, rp, rqstp->rq_cachetype, statp + 1);
+ nfsd_cache_update(rqstp, rp, rqstp->rq_cachetype, nfs_reply);
out_cached_reply:
return 1;
From: Chuck Lever <[email protected]>
[ Upstream commit bf51c52a1f3c238d72c64e14d5e7702d3a245b82 ]
nfsd_cache_csum() currently assumes that the server's RPC layer has
been advancing rq_arg.head[0].iov_base as it decodes an incoming
request, because that's the way it used to work. On entry, it
expects that buf->head[0].iov_base points to the start of the NFS
header, and excludes the already-decoded RPC header.
These days however, head[0].iov_base now points to the start of the
RPC header during all processing. It no longer points at the NFS
Call header when execution arrives at nfsd_cache_csum().
In a retransmitted RPC the XID and the NFS header are supposed to
be the same as the original message, but the contents of the
retransmitted RPC header can be different. For example, for krb5,
the GSS sequence number will be different between the two. Thus if
the RPC header is always included in the DRC checksum computation,
the checksum of the retransmitted message might not match the
checksum of the original message, even though the NFS part of these
messages is identical.
The result is that, even if a matching XID is found in the DRC,
the checksum mismatch causes the server to execute the
retransmitted RPC transaction again.
Reviewed-by: Jeff Layton <[email protected]>
Tested-by: Jeff Layton <[email protected]>
Signed-off-by: Chuck Lever <[email protected]>
---
fs/nfsd/cache.h | 4 ++-
fs/nfsd/nfscache.c | 64 +++++++++++++++++++++++++++++++++++-----------------
fs/nfsd/nfssvc.c | 10 +++++++-
3 files changed, 54 insertions(+), 24 deletions(-)
diff --git a/fs/nfsd/cache.h b/fs/nfsd/cache.h
index 929248c6ca84..4cbe0434cbb8 100644
--- a/fs/nfsd/cache.h
+++ b/fs/nfsd/cache.h
@@ -84,8 +84,8 @@ int nfsd_net_reply_cache_init(struct nfsd_net *nn);
void nfsd_net_reply_cache_destroy(struct nfsd_net *nn);
int nfsd_reply_cache_init(struct nfsd_net *);
void nfsd_reply_cache_shutdown(struct nfsd_net *);
-int nfsd_cache_lookup(struct svc_rqst *rqstp,
- struct nfsd_cacherep **cacherep);
+int nfsd_cache_lookup(struct svc_rqst *rqstp, unsigned int start,
+ unsigned int len, struct nfsd_cacherep **cacherep);
void nfsd_cache_update(struct svc_rqst *rqstp, struct nfsd_cacherep *rp,
int cachetype, __be32 *statp);
int nfsd_reply_cache_stats_show(struct seq_file *m, void *v);
diff --git a/fs/nfsd/nfscache.c b/fs/nfsd/nfscache.c
index abb453be71ca..6cd36af2f97e 100644
--- a/fs/nfsd/nfscache.c
+++ b/fs/nfsd/nfscache.c
@@ -368,33 +368,52 @@ nfsd_reply_cache_scan(struct shrinker *shrink, struct shrink_control *sc)
return freed;
}
-/*
- * Walk an xdr_buf and get a CRC for at most the first RC_CSUMLEN bytes
+/**
+ * nfsd_cache_csum - Checksum incoming NFS Call arguments
+ * @buf: buffer containing a whole RPC Call message
+ * @start: starting byte of the NFS Call header
+ * @remaining: size of the NFS Call header, in bytes
+ *
+ * Compute a weak checksum of the leading bytes of an NFS procedure
+ * call header to help verify that a retransmitted Call matches an
+ * entry in the duplicate reply cache.
+ *
+ * To avoid assumptions about how the RPC message is laid out in
+ * @buf and what else it might contain (eg, a GSS MIC suffix), the
+ * caller passes us the exact location and length of the NFS Call
+ * header.
+ *
+ * Returns a 32-bit checksum value, as defined in RFC 793.
*/
-static __wsum
-nfsd_cache_csum(struct svc_rqst *rqstp)
+static __wsum nfsd_cache_csum(struct xdr_buf *buf, unsigned int start,
+ unsigned int remaining)
{
+ unsigned int base, len;
+ struct xdr_buf subbuf;
+ __wsum csum = 0;
+ void *p;
int idx;
- unsigned int base;
- __wsum csum;
- struct xdr_buf *buf = &rqstp->rq_arg;
- const unsigned char *p = buf->head[0].iov_base;
- size_t csum_len = min_t(size_t, buf->head[0].iov_len + buf->page_len,
- RC_CSUMLEN);
- size_t len = min(buf->head[0].iov_len, csum_len);
+
+ if (remaining > RC_CSUMLEN)
+ remaining = RC_CSUMLEN;
+ if (xdr_buf_subsegment(buf, &subbuf, start, remaining))
+ return csum;
/* rq_arg.head first */
- csum = csum_partial(p, len, 0);
- csum_len -= len;
+ if (subbuf.head[0].iov_len) {
+ len = min_t(unsigned int, subbuf.head[0].iov_len, remaining);
+ csum = csum_partial(subbuf.head[0].iov_base, len, csum);
+ remaining -= len;
+ }
/* Continue into page array */
- idx = buf->page_base / PAGE_SIZE;
- base = buf->page_base & ~PAGE_MASK;
- while (csum_len) {
- p = page_address(buf->pages[idx]) + base;
- len = min_t(size_t, PAGE_SIZE - base, csum_len);
+ idx = subbuf.page_base / PAGE_SIZE;
+ base = subbuf.page_base & ~PAGE_MASK;
+ while (remaining) {
+ p = page_address(subbuf.pages[idx]) + base;
+ len = min_t(unsigned int, PAGE_SIZE - base, remaining);
csum = csum_partial(p, len, csum);
- csum_len -= len;
+ remaining -= len;
base = 0;
++idx;
}
@@ -465,6 +484,8 @@ nfsd_cache_insert(struct nfsd_drc_bucket *b, struct nfsd_cacherep *key,
/**
* nfsd_cache_lookup - Find an entry in the duplicate reply cache
* @rqstp: Incoming Call to find
+ * @start: starting byte in @rqstp->rq_arg of the NFS Call header
+ * @len: size of the NFS Call header, in bytes
* @cacherep: OUT: DRC entry for this request
*
* Try to find an entry matching the current call in the cache. When none
@@ -478,7 +499,8 @@ nfsd_cache_insert(struct nfsd_drc_bucket *b, struct nfsd_cacherep *key,
* %RC_REPLY: Reply from cache
* %RC_DROPIT: Do not process the request further
*/
-int nfsd_cache_lookup(struct svc_rqst *rqstp, struct nfsd_cacherep **cacherep)
+int nfsd_cache_lookup(struct svc_rqst *rqstp, unsigned int start,
+ unsigned int len, struct nfsd_cacherep **cacherep)
{
struct nfsd_net *nn;
struct nfsd_cacherep *rp, *found;
@@ -494,7 +516,7 @@ int nfsd_cache_lookup(struct svc_rqst *rqstp, struct nfsd_cacherep **cacherep)
goto out;
}
- csum = nfsd_cache_csum(rqstp);
+ csum = nfsd_cache_csum(&rqstp->rq_arg, start, len);
/*
* Since the common case is a cache miss followed by an insert,
diff --git a/fs/nfsd/nfssvc.c b/fs/nfsd/nfssvc.c
index 378ec82bd390..a87e9ef61386 100644
--- a/fs/nfsd/nfssvc.c
+++ b/fs/nfsd/nfssvc.c
@@ -988,6 +988,7 @@ int nfsd_dispatch(struct svc_rqst *rqstp)
const struct svc_procedure *proc = rqstp->rq_procinfo;
__be32 *statp = rqstp->rq_accept_statp;
struct nfsd_cacherep *rp;
+ unsigned int start, len;
__be32 *nfs_reply;
/*
@@ -996,11 +997,18 @@ int nfsd_dispatch(struct svc_rqst *rqstp)
*/
rqstp->rq_cachetype = proc->pc_cachetype;
+ /*
+ * ->pc_decode advances the argument stream past the NFS
+ * Call header, so grab the header's starting location and
+ * size now for the call to nfsd_cache_lookup().
+ */
+ start = xdr_stream_pos(&rqstp->rq_arg_stream);
+ len = xdr_stream_remaining(&rqstp->rq_arg_stream);
if (!proc->pc_decode(rqstp, &rqstp->rq_arg_stream))
goto out_decode_err;
rp = NULL;
- switch (nfsd_cache_lookup(rqstp, &rp)) {
+ switch (nfsd_cache_lookup(rqstp, start, len, &rp)) {
case RC_DOIT:
break;
case RC_REPLY:
> On Nov 28, 2023, at 4:58 PM, Chuck Lever <[email protected]> wrote:
>
> Backport of upstream fixes to NFSD's duplicate reply cache. These
> have been hand-applied and tested with the same reproducer as was
> used to create the upstream fixes.
These applied with fuzz and offset but no rejection.
> ---
>
> Chuck Lever (2):
> NFSD: Fix "start of NFS reply" pointer passed to nfsd_cache_update()
> NFSD: Fix checksum mismatches in the duplicate reply cache
>
>
> fs/nfsd/cache.h | 4 +--
> fs/nfsd/nfscache.c | 64 +++++++++++++++++++++++++++++++---------------
> fs/nfsd/nfssvc.c | 14 ++++++++--
> 3 files changed, 57 insertions(+), 25 deletions(-)
>
> --
> Chuck Lever
>
>
--
Chuck Lever
On Tue, Nov 28, 2023 at 10:05:45PM +0000, Chuck Lever III wrote:
>
>
> > On Nov 28, 2023, at 4:58 PM, Chuck Lever <[email protected]> wrote:
> >
> > Backport of upstream fixes to NFSD's duplicate reply cache. These
> > have been hand-applied and tested with the same reproducer as was
> > used to create the upstream fixes.
>
> These applied with fuzz and offset but no rejection.
All now queued up, thanks.
greg k-h