If userspace passes a start address that is out of bounds, _dat_walk_gfn_range() will fail with -EFAULT, but state.end will not be touched and will stay 0. This will cause *count to underflow and report a very high number, and the function will end up erroneously reporting success. Fix by only setting *count if the end address is not smaller than the starting address. This way invalid starting addresses will correctly return -EFAULT and *count will correctly indicate that no values have been returned. Fixes: 7b368470e1a4 ("KVM: s390: KVM page table management functions: CMMA") Signed-off-by: Claudio Imbrenda --- arch/s390/kvm/dat.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/s390/kvm/dat.c b/arch/s390/kvm/dat.c index 4a41c0247ffa..cffac7782c4b 100644 --- a/arch/s390/kvm/dat.c +++ b/arch/s390/kvm/dat.c @@ -1209,7 +1209,7 @@ int dat_peek_cmma(gfn_t start, union asce asce, unsigned int *count, u8 *values) int rc; rc = _dat_walk_gfn_range(start, start + *count, asce, &ops, DAT_WALK_DEFAULT, &state); - *count = state.end - start; + *count = state.end >= start ? state.end - start : 0; /* Return success if at least one value was saved, otherwise an error. */ return (rc == -EFAULT && *count > 0) ? 0 : rc; } -- 2.54.0