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s390/vfio_ccw: Fix out of bounds check on CCW array

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The routine ccwchain_calc_length() counts the number of channel
command words (CCWs) that are chained together in a single channel
program, and rejects anything larger than CCWCHAIN_LEN_MAX (256) CCWs.

The loop itself is "do..while (count < 257)", and while the logic in
is_cpa_within_range() correctly adjusts between the 0-index array of
CCWs and the count of CCWs starting at 1, this means it would look
at a possible 257th CCW before ending the loop and (correctly)
returning an error.

Fix this by restructuring the loop to break as soon as 256 CCWs
(thus indexes 0-255) are examined, without looking at memory
outside the range.

Fixes: 0a19e61e6d ("vfio: ccw: introduce channel program interfaces")
Cc: stable@vger.kernel.org
Reviewed-by: Matthew Rosato <mjrosato@linux.ibm.com>
Signed-off-by: Eric Farman <farman@linux.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@linux.ibm.com>
This commit is contained in:
Eric Farman 2026-07-28 05:30:15 +02:00 committed by Christian Borntraeger
parent 5405c90d6a
commit a005b7f1a4
1 changed files with 5 additions and 12 deletions
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17
drivers/s390/cio/vfio_ccw_cp.c
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@ -377,11 +377,9 @@ static void ccwchain_cda_free(struct ccwchain *chain, int idx)
static int ccwchain_calc_length(u64 iova, struct channel_program *cp)
{
struct ccw1 *ccw = cp->guest_cp;
int cnt = 0;
do {
cnt++;
int cnt;
for (cnt = 1; cnt <= CCWCHAIN_LEN_MAX; cnt++, ccw++) {
/*
* We want to keep counting if the current CCW has the
* command-chaining flag enabled, or if it is a TIC CCW
@ -391,15 +389,10 @@ static int ccwchain_calc_length(u64 iova, struct channel_program *cp)
* after the TIC, depending on the results of its operation.
*/
if (!ccw_is_chain(ccw) && !is_tic_within_range(ccw, iova, cnt))
break;
return cnt;
}
ccw++;
} while (cnt < CCWCHAIN_LEN_MAX + 1);
if (cnt == CCWCHAIN_LEN_MAX + 1)
cnt = -EINVAL;
return cnt;
return -EINVAL;
}
static int tic_target_chain_exists(struct ccw1 *tic, struct channel_program *cp)