nfsclient: Protest loudly when GETATTR responses are invalid

BROKEN NFS SERVER OR MIDDLEWARE: Certain WAN "accelerators" attempt to cache
NFS GETATTR traffic, but actually corrupt it (e.g., responding to requests
with attributes for totally different files).

Warn very verbosely when this is detected. Linux' NFS client has a similar
warning.

Adds a sysctl/tunable (vfs.nfs.fileid_maxwarnings) to configure the quantity
of warnings; default to 10. (Zero disables; -1 is unlimited.)

Adds a failpoint to aid in validating the warning / behavior with a
non-broken server. Use something like:

    sysctl 'debug.fail_point.nfscl_force_fileid_warning=10%return(1)'

Reviewed by:	rmacklem
Approved by:	markj (mentor)
Sponsored by:	EMC / Isilon Storage Division
Differential Revision:	https://reviews.freebsd.org/D3304

sys/fs/nfsclient/nfs_clport.c

@@ -42,7 +42,9 @@ __FBSDID("$FreeBSD$");
  * generally, I don't like #includes inside .h files, but it seems to
  * be the easiest way to handle the port.
  */
+#include <sys/fail.h>
 #include <sys/hash.h>
+#include <sys/sysctl.h>
 #include <fs/nfs/nfsport.h>
 #include <netinet/if_ether.h>
 #include <net/if_types.h>
@@ -83,6 +85,16 @@ NFSDLOCKMUTEX;
 
 extern void (*ncl_call_invalcaches)(struct vnode *);
 
+SYSCTL_DECL(_vfs_nfs);
+static int ncl_fileid_maxwarnings = 10;
+SYSCTL_INT(_vfs_nfs, OID_AUTO, fileid_maxwarnings, CTLFLAG_RWTUN,
+    &ncl_fileid_maxwarnings, 0,
+    "Limit fileid corruption warnings; 0 is off; -1 is unlimited");
+static volatile int ncl_fileid_nwarnings;
+
+static void nfscl_warn_fileid(struct nfsmount *, struct nfsvattr *,
+    struct nfsvattr *);
+
 /*
  * Comparison function for vfs_hash functions.
  */
@@ -343,6 +355,37 @@ nfscl_ngetreopen(struct mount *mntp, u_int8_t *fhp, int fhsize,
 	return (EINVAL);
 }
 
+static void
+nfscl_warn_fileid(struct nfsmount *nmp, struct nfsvattr *oldnap,
+    struct nfsvattr *newnap)
+{
+	int off;
+
+	if (ncl_fileid_maxwarnings >= 0 &&
+	    ncl_fileid_nwarnings >= ncl_fileid_maxwarnings)
+		return;
+	off = 0;
+	if (ncl_fileid_maxwarnings >= 0) {
+		if (++ncl_fileid_nwarnings >= ncl_fileid_maxwarnings)
+			off = 1;
+	}
+
+	printf("newnfs: server '%s' error: fileid changed. "
+	    "fsid %jx:%jx: expected fileid %#jx, got %#jx. "
+	    "(BROKEN NFS SERVER OR MIDDLEWARE)\n",
+	    nmp->nm_com.nmcom_hostname,
+	    (uintmax_t)nmp->nm_fsid[0],
+	    (uintmax_t)nmp->nm_fsid[1],
+	    (uintmax_t)oldnap->na_fileid,
+	    (uintmax_t)newnap->na_fileid);
+
+	if (off)
+		printf("newnfs: Logged %d times about fileid corruption; "
+		    "going quiet to avoid spamming logs excessively. (Limit "
+		    "is: %d).\n", ncl_fileid_nwarnings,
+		    ncl_fileid_maxwarnings);
+}
+
 /*
  * Load the attribute cache (that lives in the nfsnode entry) with
  * the attributes of the second argument and
@@ -361,7 +404,11 @@ nfscl_loadattrcache(struct vnode **vpp, struct nfsvattr *nap, void *nvaper,
 	struct nfsmount *nmp;
 	struct timespec mtime_save;
 	u_quad_t nsize;
-	int setnsize;
+	int setnsize, error, force_fid_err;
+
+	error = 0;
+	setnsize = 0;
+	nsize = 0;
 
 	/*
 	 * If v_type == VNON it is a new node, so fill in the v_type,
@@ -389,6 +436,34 @@ nfscl_loadattrcache(struct vnode **vpp, struct nfsvattr *nap, void *nvaper,
 		np->n_vattr.na_fsid = nap->na_fsid;
 		np->n_vattr.na_mode = nap->na_mode;
 	} else {
+		force_fid_err = 0;
+		KFAIL_POINT_ERROR(DEBUG_FP, nfscl_force_fileid_warning,
+		    force_fid_err);
+		/*
+		 * BROKEN NFS SERVER OR MIDDLEWARE
+		 *
+		 * Certain NFS servers (certain old proprietary filers ca.
+		 * 2006) or broken middleboxes (e.g. WAN accelerator products)
+		 * will respond to GETATTR requests with results for a
+		 * different fileid.
+		 *
+		 * The WAN accelerator we've observed not only serves stale
+		 * cache results for a given file, it also occasionally serves
+		 * results for wholly different files.  This causes surprising
+		 * problems; for example the cached size attribute of a file
+		 * may truncate down and then back up, resulting in zero
+		 * regions in file contents read by applications.  We observed
+		 * this reliably with Clang and .c files during parallel build.
+		 * A pcap revealed packet fragmentation and GETATTR RPC
+		 * responses with wholly wrong fileids.
+		 */
+		if ((np->n_vattr.na_fileid != 0 &&
+		     np->n_vattr.na_fileid != nap->na_fileid) ||
+		    force_fid_err) {
+			nfscl_warn_fileid(nmp, &np->n_vattr, nap);
+			error = EIDRM;
+			goto out;
+		}
 		NFSBCOPY((caddr_t)nap, (caddr_t)&np->n_vattr,
 		    sizeof (struct nfsvattr));
 	}
@@ -419,8 +494,6 @@ nfscl_loadattrcache(struct vnode **vpp, struct nfsvattr *nap, void *nvaper,
 	} else
 		vap->va_fsid = vp->v_mount->mnt_stat.f_fsid.val[0];
 	np->n_attrstamp = time_second;
-	setnsize = 0;
-	nsize = 0;
 	if (vap->va_size != np->n_size) {
 		if (vap->va_type == VREG) {
 			if (dontshrink && vap->va_size < np->n_size) {
@@ -490,14 +563,16 @@ nfscl_loadattrcache(struct vnode **vpp, struct nfsvattr *nap, void *nvaper,
 				vaper->va_mtime = np->n_mtim;
 		}
 	}
+
+out:
 #ifdef KDTRACE_HOOKS
 	if (np->n_attrstamp != 0)
-		KDTRACE_NFS_ATTRCACHE_LOAD_DONE(vp, vap, 0);
+		KDTRACE_NFS_ATTRCACHE_LOAD_DONE(vp, vap, error);
 #endif
 	NFSUNLOCKNODE(np);
 	if (setnsize)
 		vnode_pager_setsize(vp, nsize);
-	return (0);
+	return (error);
 }
 
 /*