[PATCH] fib6: fix signedness in common root build

[Robert Sanford <rsanford2@gmail.com>]

From: Robert Sanford <rsanford@akamai.com>

In build_common_root(), get_idx() returns a uint32_t, but the result
was stored in an int. When the high bit was set, the value became
negative and was then sign-extended when passed as the uint64_t index
to get_tbl_p_by_idx(), producing a bogus table pointer.

Make idx and prev_idx unsigned, and use a separate signed tbl8_idx for
the tbl8_alloc() result, since it returns a negative value on error.
Widen to 64 bits before shifting or multiplying so the intermediate
results cannot overflow.

Fixes: c3e12e0f03 ("fib: add dataplane algorithm for IPv6")
Cc: stable@dpdk.org

Signed-off-by: Robert Sanford <rsanford@akamai.com>
---
 lib/fib/trie.c | 17 +++++++++--------
 1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/lib/fib/trie.c b/lib/fib/trie.c
index 187360d1c8..dc57127dc9 100644
--- a/lib/fib/trie.c
+++ b/lib/fib/trie.c
@@ -317,7 +317,8 @@ build_common_root(struct rte_trie_tbl *dp, const struct rte_ipv6_addr *ip,
 	void *tbl_ptr = NULL;
 	uint64_t *cur_tbl;
 	uint64_t val;
-	int i, j, idx, prev_idx = 0;
+	uint32_t idx, prev_idx = 0;
+	int i, j, tbl8_idx;
 
 	cur_tbl = dp->tbl24;
 	for (i = 3, j = 0; i <= common_bytes; i++) {
@@ -325,20 +326,20 @@ build_common_root(struct rte_trie_tbl *dp, const struct rte_ipv6_addr *ip,
 		val = get_tbl_val_by_idx(cur_tbl, idx, dp->nh_sz);
 		tbl_ptr = get_tbl_p_by_idx(cur_tbl, idx, dp->nh_sz);
 		if ((val & TRIE_EXT_ENT) != TRIE_EXT_ENT) {
-			idx = tbl8_alloc(dp, val);
-			if (unlikely(idx < 0))
-				return idx;
-			write_to_dp(tbl_ptr, (idx << 1) |
+			tbl8_idx = tbl8_alloc(dp, val);
+			if (unlikely(tbl8_idx < 0))
+				return tbl8_idx;
+			write_to_dp(tbl_ptr, ((uint64_t)tbl8_idx << 1) |
 				TRIE_EXT_ENT, dp->nh_sz, 1);
-			prev_idx = idx;
+			prev_idx = tbl8_idx;
 		} else
 			prev_idx = val >> 1;
 
 		j = i;
 		cur_tbl = dp->tbl8;
 	}
-	*tbl = get_tbl_p_by_idx(cur_tbl, prev_idx * TRIE_TBL8_GRP_NUM_ENT,
-		dp->nh_sz);
+	*tbl = get_tbl_p_by_idx(cur_tbl,
+		(uint64_t)prev_idx * TRIE_TBL8_GRP_NUM_ENT, dp->nh_sz);
 	return 0;
 }
 
-- 
2.34.1