Re: [Qemu-devel] [PATCH] spapr: fix buffer-overflow

[David Gibson]

On Thu, Mar 23, 2017 at 02:04:55PM +0400, Marc-André Lureau wrote:
> Running postcopy-test with ASAN produces the following error:
> 
> QTEST_QEMU_BINARY=ppc64-softmmu/qemu-system-ppc64  tests/postcopy-test
> ...
> =================================================================
> ==23641==ERROR: AddressSanitizer: heap-buffer-overflow on address 
> 0x7f1556600000 at pc 0x55b8e9d28208 bp 0x7f1555f4d3c0 sp 0x7f1555f4d3b0
> READ of size 8 at 0x7f1556600000 thread T6
>     #0 0x55b8e9d28207 in htab_save_first_pass 
> /home/elmarco/src/qq/hw/ppc/spapr.c:1528
>     #1 0x55b8e9d2939c in htab_save_iterate 
> /home/elmarco/src/qq/hw/ppc/spapr.c:1665
>     #2 0x55b8e9beae3a in qemu_savevm_state_iterate 
> /home/elmarco/src/qq/migration/savevm.c:1044
>     #3 0x55b8ea677733 in migration_thread 
> /home/elmarco/src/qq/migration/migration.c:1976
>     #4 0x7f15845f46c9 in start_thread (/lib64/libpthread.so.0+0x76c9)
>     #5 0x7f157d9d0f7e in clone (/lib64/libc.so.6+0x107f7e)
> 
> 0x7f1556600000 is located 0 bytes to the right of 2097152-byte region 
> [0x7f1556400000,0x7f1556600000)
> allocated by thread T0 here:
>     #0 0x7f159bb76980 in posix_memalign (/lib64/libasan.so.3+0xc7980)
>     #1 0x55b8eab185b2 in qemu_try_memalign 
> /home/elmarco/src/qq/util/oslib-posix.c:106
>     #2 0x55b8eab186c8 in qemu_memalign 
> /home/elmarco/src/qq/util/oslib-posix.c:122
>     #3 0x55b8e9d268a8 in spapr_reallocate_hpt 
> /home/elmarco/src/qq/hw/ppc/spapr.c:1214
>     #4 0x55b8e9d26e04 in ppc_spapr_reset 
> /home/elmarco/src/qq/hw/ppc/spapr.c:1261
>     #5 0x55b8ea12e913 in qemu_system_reset /home/elmarco/src/qq/vl.c:1697
>     #6 0x55b8ea13fa40 in main /home/elmarco/src/qq/vl.c:4679
>     #7 0x7f157d8e9400 in __libc_start_main (/lib64/libc.so.6+0x20400)
> 
> Thread T6 created by T0 here:
>     #0 0x7f159bae0488 in __interceptor_pthread_create 
> (/lib64/libasan.so.3+0x31488)
>     #1 0x55b8eab1d9cb in qemu_thread_create 
> /home/elmarco/src/qq/util/qemu-thread-posix.c:465
>     #2 0x55b8ea67874c in migrate_fd_connect 
> /home/elmarco/src/qq/migration/migration.c:2096
>     #3 0x55b8ea66cbb0 in migration_channel_connect 
> /home/elmarco/src/qq/migration/migration.c:500
>     #4 0x55b8ea678f38 in socket_outgoing_migration 
> /home/elmarco/src/qq/migration/socket.c:87
>     #5 0x55b8eaa5a03a in qio_task_complete /home/elmarco/src/qq/io/task.c:142
>     #6 0x55b8eaa599cc in gio_task_thread_result 
> /home/elmarco/src/qq/io/task.c:88
>     #7 0x7f15823e38e6  (/lib64/libglib-2.0.so.0+0x468e6)
> SUMMARY: AddressSanitizer: heap-buffer-overflow 
> /home/elmarco/src/qq/hw/ppc/spapr.c:1528 in htab_save_first_pass
> 
> index seems to be wrongly incremented, unless I miss something that
> would be worth a comment.
> 
> Signed-off-by: Marc-André Lureau <address@hidden>

Oh my.  That's an impressively embarrassing bug.  As well as the
overrun itself, we're marking the wrong HPTEs clean.  I'm kind of
surprised we haven't seen this bite already.  Anyway, I've applied to
ppc-for-2.9, and I'll send a pull request ASAP.

> ---
>  hw/ppc/spapr.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> index 6ee566d658..63439811d5 100644
> --- a/hw/ppc/spapr.c
> +++ b/hw/ppc/spapr.c
> @@ -1524,16 +1524,16 @@ static void htab_save_first_pass(QEMUFile *f, 
> sPAPRMachineState *spapr,
>          /* Consume invalid HPTEs */
>          while ((index < htabslots)
>                 && !HPTE_VALID(HPTE(spapr->htab, index))) {
> -            index++;
>              CLEAN_HPTE(HPTE(spapr->htab, index));
> +            index++;
>          }
>  
>          /* Consume valid HPTEs */
>          chunkstart = index;
>          while ((index < htabslots) && (index - chunkstart < USHRT_MAX)
>                 && HPTE_VALID(HPTE(spapr->htab, index))) {
> -            index++;
>              CLEAN_HPTE(HPTE(spapr->htab, index));
> +            index++;
>          }
>  
>          if (index > chunkstart) {

-- 
David Gibson                    | 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

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