Re: [PATCH v4 6/8] tcp: Cast operands of sequence comparison macros to uint32_t before using them

On Tue, Sep 09, 2025 at 08:16:53PM +0200, Stefano Brivio wrote:

Otherwise, passing signed types causes automatic promotion of the result of the subtractions as well, which is not what we want, as these macros rely on unsigned 32-bit arithmetic.

The next patch introduces a ssize_t operand for SEQ_LE, illustrating the issue.

Signed-off-by: Stefano Brivio

Reviewed-by: David Gibson C macros and promotion rules strike again :/. Personally I'd probably switch to inline functions, but this is fine too.

--- tcp_internal.h | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/tcp_internal.h b/tcp_internal.h index d0009f8..ce6fee2 100644 --- a/tcp_internal.h +++ b/tcp_internal.h @@ -21,10 +21,14 @@ sizeof(struct ipv6hdr), \ sizeof(uint32_t))

-#define SEQ_LE(a, b) ((b) - (a) < MAX_WINDOW) -#define SEQ_LT(a, b) ((b) - (a) - 1 < MAX_WINDOW) -#define SEQ_GE(a, b) ((a) - (b) < MAX_WINDOW) -#define SEQ_GT(a, b) ((a) - (b) - 1 < MAX_WINDOW) +#define SEQ_LE(a, b) \ + ((uint32_t)(b) - (uint32_t)(a) < MAX_WINDOW) +#define SEQ_LT(a, b) \ + ((uint32_t)(b) - (uint32_t)(a) - 1 < MAX_WINDOW) +#define SEQ_GE(a, b) \ + ((uint32_t)(a) - (uint32_t)(b) < MAX_WINDOW) +#define SEQ_GT(a, b) \ + ((uint32_t)(a) - (uint32_t)(b) - 1 < MAX_WINDOW)

#define FIN (1 << 0) #define SYN (1 << 1) -- 2.43.0

-- David Gibson (he or they) | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you, not the other way | around. http://www.ozlabs.org/~dgibson