libceph: make decode_pool() more resilient against corrupted osdmaps

If the osdmap is (maliciously) corrupted such that the encoded length
of ceph_pg_pool envelope is less than what is expected for a particular
encoding version, out-of-bounds reads may ensue because the only bounds
check that is there is based on that length value.

This patch adds explicit bounds checks for each field that is decoded
or skipped.

Cc: [e-mail]
Reported-by: ziming zhang <[e-mail]>
Signed-off-by: Ilya Dryomov <[e-mail]>
Reviewed-by: Xiubo Li <[e-mail]>
Tested-by: ziming zhang <[e-mail]>

net/ceph/osdmap.c

···
 	ceph_decode_need(p, end, len, bad);
 	pool_end = *p + len;
 
+	ceph_decode_need(p, end, 4 + 4 + 4, bad);
 	pi->type = ceph_decode_8(p);
 	pi->size = ceph_decode_8(p);
 	pi->crush_ruleset = ceph_decode_8(p);
 	pi->object_hash = ceph_decode_8(p);
-
 	pi->pg_num = ceph_decode_32(p);
 	pi->pgp_num = ceph_decode_32(p);
 
-	*p += 4 + 4;  /* skip lpg* */
-	*p += 4;      /* skip last_change */
-	*p += 8 + 4;  /* skip snap_seq, snap_epoch */
+	/* lpg*, last_change, snap_seq, snap_epoch */
+	ceph_decode_skip_n(p, end, 8 + 4 + 8 + 4, bad);
 
 	/* skip snaps */
-	num = ceph_decode_32(p);
+	ceph_decode_32_safe(p, end, num, bad);
 	while (num--) {
-		*p += 8;  /* snapid key */
-		*p += 1 + 1; /* versions */
-		len = ceph_decode_32(p);
-		*p += len;
+		/* snapid key, pool snap (with versions) */
+		ceph_decode_skip_n(p, end, 8 + 2, bad);
+		ceph_decode_skip_string(p, end, bad);
 	}
 
-	/* skip removed_snaps */
-	num = ceph_decode_32(p);
-	*p += num * (8 + 8);
+	/* removed_snaps */
+	ceph_decode_skip_map(p, end, 64, 64, bad);
 
+	ceph_decode_need(p, end, 8 + 8 + 4, bad);
 	*p += 8;  /* skip auid */
 	pi->flags = ceph_decode_64(p);
 	*p += 4;  /* skip crash_replay_interval */
 
 	if (ev >= 7)
-		pi->min_size = ceph_decode_8(p);
+		ceph_decode_8_safe(p, end, pi->min_size, bad);
 	else
 		pi->min_size = pi->size - pi->size / 2;
 
 	if (ev >= 8)
-		*p += 8 + 8;  /* skip quota_max_* */
+		/* quota_max_* */
+		ceph_decode_skip_n(p, end, 8 + 8, bad);
 
 	if (ev >= 9) {
-		/* skip tiers */
-		num = ceph_decode_32(p);
-		*p += num * 8;
+		/* tiers */
+		ceph_decode_skip_set(p, end, 64, bad);
 
+		ceph_decode_need(p, end, 8 + 1 + 8 + 8, bad);
 		*p += 8;  /* skip tier_of */
 		*p += 1;  /* skip cache_mode */
-
 		pi->read_tier = ceph_decode_64(p);
 		pi->write_tier = ceph_decode_64(p);
 	} else {
···
 		pi->write_tier = -1;
 	}
 
-	if (ev >= 10) {
-		/* skip properties */
-		num = ceph_decode_32(p);
-		while (num--) {
-			len = ceph_decode_32(p);
-			*p += len; /* key */
-			len = ceph_decode_32(p);
-			*p += len; /* val */
-		}
-	}
+	if (ev >= 10)
+		/* properties */
+		ceph_decode_skip_map(p, end, string, string, bad);
 
 	if (ev >= 11) {
-		/* skip hit_set_params */
-		*p += 1 + 1; /* versions */
-		len = ceph_decode_32(p);
-		*p += len;
+		/* hit_set_params (with versions) */
+		ceph_decode_skip_n(p, end, 2, bad);
+		ceph_decode_skip_string(p, end, bad);
 
-		*p += 4; /* skip hit_set_period */
-		*p += 4; /* skip hit_set_count */
+		/* hit_set_period, hit_set_count */
+		ceph_decode_skip_n(p, end, 4 + 4, bad);
 	}
 
 	if (ev >= 12)
-		*p += 4; /* skip stripe_width */
+		/* stripe_width */
+		ceph_decode_skip_32(p, end, bad);
 
-	if (ev >= 13) {
-		*p += 8; /* skip target_max_bytes */
-		*p += 8; /* skip target_max_objects */
-		*p += 4; /* skip cache_target_dirty_ratio_micro */
-		*p += 4; /* skip cache_target_full_ratio_micro */
-		*p += 4; /* skip cache_min_flush_age */
-		*p += 4; /* skip cache_min_evict_age */
-	}
+	if (ev >= 13)
+		/* target_max_*, cache_target_*, cache_min_* */
+		ceph_decode_skip_n(p, end, 16 + 8 + 8, bad);
 
-	if (ev >=  14) {
-		/* skip erasure_code_profile */
-		len = ceph_decode_32(p);
-		*p += len;
-	}
+	if (ev >= 14)
+		/* erasure_code_profile */
+		ceph_decode_skip_string(p, end, bad);
 
 	/*
 	 * last_force_op_resend_preluminous, will be overridden if the
 	 * map was encoded with RESEND_ON_SPLIT
 	 */
 	if (ev >= 15)
-		pi->last_force_request_resend = ceph_decode_32(p);
+		ceph_decode_32_safe(p, end, pi->last_force_request_resend, bad);
 	else
 		pi->last_force_request_resend = 0;
 
 	if (ev >= 16)
-		*p += 4; /* skip min_read_recency_for_promote */
+		/* min_read_recency_for_promote */
+		ceph_decode_skip_32(p, end, bad);
 
 	if (ev >= 17)
-		*p += 8; /* skip expected_num_objects */
+		/* expected_num_objects */
+		ceph_decode_skip_64(p, end, bad);
 
 	if (ev >= 19)
-		*p += 4; /* skip cache_target_dirty_high_ratio_micro */
+		/* cache_target_dirty_high_ratio_micro */
+		ceph_decode_skip_32(p, end, bad);
 
 	if (ev >= 20)
-		*p += 4; /* skip min_write_recency_for_promote */
+		/* min_write_recency_for_promote */
+		ceph_decode_skip_32(p, end, bad);
 
 	if (ev >= 21)
-		*p += 1; /* skip use_gmt_hitset */
+		/* use_gmt_hitset */
+		ceph_decode_skip_8(p, end, bad);
 
 	if (ev >= 22)
-		*p += 1; /* skip fast_read */
+		/* fast_read */
+		ceph_decode_skip_8(p, end, bad);
 
-	if (ev >= 23) {
-		*p += 4; /* skip hit_set_grade_decay_rate */
-		*p += 4; /* skip hit_set_search_last_n */
-	}
+	if (ev >= 23)
+		/* hit_set_grade_decay_rate, hit_set_search_last_n */
+		ceph_decode_skip_n(p, end, 4 + 4, bad);
 
 	if (ev >= 24) {
-		/* skip opts */
-		*p += 1 + 1; /* versions */
-		len = ceph_decode_32(p);
-		*p += len;
+		/* opts (with versions) */
+		ceph_decode_skip_n(p, end, 2, bad);
+		ceph_decode_skip_string(p, end, bad);
 	}
 
 	if (ev >= 25)
-		pi->last_force_request_resend = ceph_decode_32(p);
+		ceph_decode_32_safe(p, end, pi->last_force_request_resend, bad);
 
 	/* ignore the rest */