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udp: Fix 16-bit overflow in udp_invert_portmap()

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The code in udp_invert_portmap() is written based on an incorrect
understanding of C's (arcane) integer promotion rules.  We calculate
'(in_port_t)i + delta' expecting the result to be of type in_port_t (16
bits).  However "small integer types" (those narrower than 'int') are
always promoted to int for expressions, meaning this calculation can
overrun the rdelta[] array.

Fix this, and use a new intermediate for the index, to make it very clear
what it's type is.  We also change i to unsigned, to avoid any possible
confusion from mixing signed and unsigned types.

Link: https://bugs.passt.top/show_bug.cgi?id=80
Reported-by: Laurent Jacquot <jk@lutty.net>
Suggested-by: Laurent Jacquot <jk@lutty.net>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
This commit is contained in:
David Gibson 2024-02-20 13:48:24 +11:00 committed by Stefano Brivio
parent 8954c4a91b
commit 1e6f92b995
1 changed files with 3 additions and 2 deletions
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udp.c
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@ -258,15 +258,16 @@ void udp_portmap_clear(void)
*/
static void udp_invert_portmap(struct udp_port_fwd *fwd)
{
int i;
unsigned int i;
static_assert(ARRAY_SIZE(fwd->f.delta) == ARRAY_SIZE(fwd->rdelta),
"Forward and reverse delta arrays must have same size");
for (i = 0; i < ARRAY_SIZE(fwd->f.delta); i++) {
in_port_t delta = fwd->f.delta[i];
in_port_t rport = i + delta;
if (delta)
fwd->rdelta[(in_port_t)i + delta] = NUM_PORTS - delta;
fwd->rdelta[rport] = NUM_PORTS - delta;
}
}