[PATCH 4.9 035/212] arm64: csum: Fix handling of bad packets

[Greg Kroah-Hartman]

From: Robin Murphy <robin.murphy@xxxxxxx>

[ Upstream commit 05fb3dbda187bbd9cc1cd0e97e5d6595af570ac6 ]

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: 0e455d8e80aa ("arm64: Implement optimised IP checksum helpers")
Reported-by: guodeqing <geffrey.guo@xxxxxxxxxx>
Signed-off-by: Robin Murphy <robin.murphy@xxxxxxx>
Signed-off-by: Will Deacon <will@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 arch/arm64/include/asm/checksum.h | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/include/asm/checksum.h b/arch/arm64/include/asm/checksum.h
index 09f65339d66df..e6d66c508d81b 100644
--- a/arch/arm64/include/asm/checksum.h
+++ b/arch/arm64/include/asm/checksum.h
@@ -30,16 +30,17 @@ 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(sum >> 32);
-- 
2.25.1