arm64: csum: Fix handling of bad packets

Although iph is expected to point to at least 20 bytes of valid memory, ihl may be bogus, for example on reception of a corrupt packet. If it happens to be less than 5, we really don't want to run away and dereference 16GB worth of memory until it wraps back to exactly zero... Fixes: 0e455d8 ("arm64: Implement optimised IP checksum helpers") Reported-by: guodeqing <[email protected]> Signed-off-by: Robin Murphy <[email protected]> Signed-off-by: Will Deacon <[email protected]>
devinus · Jul 30, 2020 · 05fb3db · 05fb3db
1 parent 835d1c3
commit 05fb3db
Showing 1 changed file with 3 additions and 2 deletions.
diff --git a/arch/arm64/include/asm/checksum.h b/arch/arm64/include/asm/checksum.h
@@ -24,16 +24,17 @@ static inline __sum16 ip_fast_csum(const void *iph, unsigned int ihl)
 {
 	__uint128_t tmp;
 	u64 sum;
+	int n = ihl; /* we want it signed */
 
 	tmp = *(const __uint128_t *)iph;
 	iph += 16;
-	ihl -= 4;
+	n -= 4;
 	tmp += ((tmp >> 64) | (tmp << 64));
 	sum = tmp >> 64;
 	do {
 		sum += *(const u32 *)iph;
 		iph += 4;
-	} while (--ihl);
+	} while (--n > 0);
 
 	sum += ((sum >> 32) | (sum << 32));
 	return csum_fold((__force u32)(sum >> 32));