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byte-order: Fix undefined behavior of BYTES_TO_BE32.

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A left shift that would produce a result that is not representable
by the type of the expression's result has "undefined behavior"
according to the C language standard. Avoid this by casting values
that could set the upper bit to unsigned types.

Also document and convert a macro to a function.

While we're at it, delete the unused macro BE16S_TO_BE32.

Found via gcc's undefined behavior sanitizer.

Reported-by: Lance Richardson <lrichard@redhat.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>
Acked-by: Lance Richardson <lrichard@redhat.com>
This commit is contained in:
Ben Pfaff
2017-06-12 21:51:14 -07:00
parent 6b1d462533
commit a13784ba95
2 changed files with 14 additions and 9 deletions
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21
lib/byte-order.h
View File

@@ -98,17 +98,22 @@ uint32_byteswap(uint32_t crc) {
((((ovs_be64) (VALUE)) & UINT64_C(0xff00000000000000)) >> 56))
#endif
/* Returns the ovs_be32 that you would get from:
*
* union { uint8_t b[4]; ovs_be32 be32; } x = { .b = { b0, b1, b2, b3 } };
* return x.be32;
*
* but without the undefined behavior. */
static inline ovs_be32
bytes_to_be32(uint8_t b0, uint8_t b1, uint8_t b2, uint8_t b3)
{
#if WORDS_BIGENDIAN
#define BYTES_TO_BE32(B1, B2, B3, B4) \
(OVS_FORCE ovs_be32)((uint32_t)(B1) << 24 | (B2) << 16 | (B3) << 8 | (B4))
#define BE16S_TO_BE32(B1, B2) \
(OVS_FORCE ovs_be32)((uint32_t)(B1) << 16 | (B2))
uint32_t x = ((uint32_t) b0 << 24) | (b1 << 16) | (b2 << 8) | b3;
#else
#define BYTES_TO_BE32(B1, B2, B3, B4) \
(OVS_FORCE ovs_be32)((uint32_t)(B1) | (B2) << 8 | (B3) << 16 | (B4) << 24)
#define BE16S_TO_BE32(B1, B2) \
(OVS_FORCE ovs_be32)((uint32_t)(B1) | (B2) << 16)
uint32_t x = ((uint32_t) b3 << 24) | (b2 << 16) | (b1 << 8) | b0;
#endif
return (OVS_FORCE ovs_be32) x;
}
/* These functions zero-extend big-endian values to longer ones,
* or truncate long big-endian value to shorter ones. */

2
lib/flow.c
View File

@@ -823,7 +823,7 @@ miniflow_extract(struct dp_packet *packet, struct miniflow *dst)
packet->l4_ofs = (char *)data - frame;
miniflow_push_be32(mf, nw_frag,
BYTES_TO_BE32(nw_frag, nw_tos, nw_ttl, nw_proto));
bytes_to_be32(nw_frag, nw_tos, nw_ttl, nw_proto));
if (OVS_LIKELY(!(nw_frag & FLOW_NW_FRAG_LATER))) {
if (OVS_LIKELY(nw_proto == IPPROTO_TCP)) {