6585 sha512, skein, and edonr have an unenforced dependency on extens…

…ible dataset

Reviewed by: Matthew Ahrens <[email protected]>
Reviewed by: Richard Laager <[email protected]>

In any pool without the extensible dataset feature flag already enabled,
creating a dataset with dedup set to use one of the new checksums would
result in the following panic as soon as any data was added:

panic[cpu0]/thread=ffffff0006761c40: feature_get_refcount(spa, feature,
&refcount) != 48 (0x30 != 0x30), file: ../../common/fs/zfs/zfeature.c
line 390

Inpsection showed that feature->fi_feature was 7, which is the value of
SPA_FEATURE_EXTENSIBLE_DATASET in the spa_feature enum.  This commit
adds extensible dataset as a dependency for the sha512, edonr, and skein
feature flags, which prevents the panic.

man/man5/zpool-features.5

@@ -432,5 +432,114 @@ set larger than 128KB, and will return to being \fBenabled\fR once all
 filesystems that have ever had their recordsize larger than 128KB are destroyed.
 .RE
 
+.sp
+.ne 2
+.na
+\fB\fBsha512\fR\fR
+.ad
+.RS 4n
+.TS
+l l .
+GUID	org.illumos:sha512
+READ\-ONLY COMPATIBLE	no
+DEPENDENCIES	extensible_dataset
+.TE
+
+This feature enables the use of the SHA-512/256 truncated hash algorithm
+(FIPS 180-4) for checksum and dedup. The native 64-bit arithmetic of
+SHA-512 provides an approximate 50% performance boost over SHA-256 on
+64-bit hardware and is thus a good minimum-change replacement candidate
+for systems where hash performance is important, but these systems
+cannot for whatever reason utilize the faster \fBskein\fR and
+\fBedonr\fR algorithms.
+
+When the \fBsha512\fR feature is set to \fBenabled\fR, the administrator
+can turn on the \fBsha512\fR checksum on any dataset using the
+\fBzfs set checksum=sha512\fR(1M) command.  This feature becomes
+\fBactive\fR once a \fBchecksum\fR property has been set to \fBsha512\fR,
+and will return to being \fBenabled\fR once all filesystems that have
+ever had their checksum set to \fBsha512\fR are destroyed.
+
+Booting off of pools utilizing SHA-512/256 is supported (provided that
+the updated GRUB stage2 module is installed).
+
+.RE
+
+.sp
+.ne 2
+.na
+\fB\fBskein\fR\fR
+.ad
+.RS 4n
+.TS
+l l .
+GUID	org.illumos:skein
+READ\-ONLY COMPATIBLE	no
+DEPENDENCIES	extensible_dataset
+.TE
+
+This feature enables the use of the Skein hash algorithm for checksum
+and dedup. Skein is a high-performance secure hash algorithm that was a
+finalist in the NIST SHA-3 competition. It provides a very high security
+margin and high performance on 64-bit hardware (80% faster than
+SHA-256). This implementation also utilizes the new salted checksumming
+functionality in ZFS, which means that the checksum is pre-seeded with a
+secret 256-bit random key (stored on the pool) before being fed the data
+block to be checksummed. Thus the produced checksums are unique to a
+given pool, preventing hash collision attacks on systems with dedup.
+
+When the \fBskein\fR feature is set to \fBenabled\fR, the administrator
+can turn on the \fBskein\fR checksum on any dataset using the
+\fBzfs set checksum=skein\fR(1M) command.  This feature becomes
+\fBactive\fR once a \fBchecksum\fR property has been set to \fBskein\fR,
+and will return to being \fBenabled\fR once all filesystems that have
+ever had their checksum set to \fBskein\fR are destroyed.
+
+Booting off of pools using \fBskein\fR is \fBNOT\fR supported
+-- any attempt to enable \fBskein\fR on a root pool will fail with an
+error.
+
+.RE
+
+.sp
+.ne 2
+.na
+\fB\fBedonr\fR\fR
+.ad
+.RS 4n
+.TS
+l l .
+GUID	org.illumos:edonr
+READ\-ONLY COMPATIBLE	no
+DEPENDENCIES	extensible_dataset
+.TE
+
+This feature enables the use of the Edon-R hash algorithm for checksum,
+including for nopwrite (if compression is also enabled, an overwrite of
+a block whose checksum matches the data being written will be ignored).
+In an abundance of caution, Edon-R can not be used with dedup
+(without verification).
+
+Edon-R is a very high-performance hash algorithm that was part
+of the NIST SHA-3 competition. It provides extremely high hash
+performance (over 350% faster than SHA-256), but was not selected
+because of its unsuitability as a general purpose secure hash algorithm.
+This implementation utilizes the new salted checksumming functionality
+in ZFS, which means that the checksum is pre-seeded with a secret
+256-bit random key (stored on the pool) before being fed the data block
+to be checksummed. Thus the produced checksums are unique to a given
+pool.
+
+When the \fBedonr\fR feature is set to \fBenabled\fR, the administrator
+can turn on the \fBedonr\fR checksum on any dataset using the
+\fBzfs set checksum=edonr\fR(1M) command.  This feature becomes
+\fBactive\fR once a \fBchecksum\fR property has been set to \fBedonr\fR,
+and will return to being \fBenabled\fR once all filesystems that have
+ever had their checksum set to \fBedonr\fR are destroyed.
+
+Booting off of pools using \fBedonr\fR is \fBNOT\fR supported
+-- any attempt to enable \fBedonr\fR on a root pool will fail with an
+error.
+
 .SH "SEE ALSO"
 \fBzpool\fR(8)

module/zfs/zfeature_common.c

@@ -238,16 +238,30 @@ zpool_feature_init(void)
 	    "Support for blocks larger than 128KB.",
 	    ZFEATURE_FLAG_PER_DATASET, large_blocks_deps);
 
+	static const spa_feature_t sha512_deps[] = {
+		SPA_FEATURE_EXTENSIBLE_DATASET,
+		SPA_FEATURE_NONE
+	};
 	zfeature_register(SPA_FEATURE_SHA512,
-		"org.illumos:sha512", "sha512",
-		"SHA-512/256 hash algorithm.",
-        ZFEATURE_FLAG_PER_DATASET, NULL);
+	    "org.illumos:sha512", "sha512",
+	    "SHA-512/256 hash algorithm.",
+	    ZFEATURE_FLAG_PER_DATASET, sha512_deps);
+
+	static const spa_feature_t skein_deps[] = {
+		SPA_FEATURE_EXTENSIBLE_DATASET,
+		SPA_FEATURE_NONE
+	};
 	zfeature_register(SPA_FEATURE_SKEIN,
-		"org.illumos:skein", "skein",
-		"Skein hash algorithm.",
-		ZFEATURE_FLAG_PER_DATASET, NULL);
+	    "org.illumos:skein", "skein",
+	    "Skein hash algorithm.",
+	    ZFEATURE_FLAG_PER_DATASET, skein_deps);
+
+	static const spa_feature_t edonr_deps[] = {
+		SPA_FEATURE_EXTENSIBLE_DATASET,
+		SPA_FEATURE_NONE
+	};
 	zfeature_register(SPA_FEATURE_EDONR,
 		"org.illumos:edonr", "edonr",
 	    "Edon-R hash algorithm.",
-		ZFEATURE_FLAG_PER_DATASET, NULL);
+	    ZFEATURE_FLAG_PER_DATASET, edonr_deps);
 }