* [PATCH for-5.1] block: fix bdrv_aio_cancel() for ENOMEDIUM requests
@ 2020-07-20 10:01 Stefan Hajnoczi
2020-07-21 10:01 ` Max Reitz
0 siblings, 1 reply; 2+ messages in thread
From: Stefan Hajnoczi @ 2020-07-20 10:01 UTC (permalink / raw)
To: qemu-devel
Cc: Kevin Wolf, qemu-block, qemu-stable, Max Reitz,
Alexander Bulekov, Stefan Hajnoczi, Philippe Mathieu-Daudé
bdrv_aio_cancel() calls aio_poll() on the AioContext for the given I/O
request until it has completed. ENOMEDIUM requests are special because
there is no BlockDriverState when the drive has no medium!
Define a .get_aio_context() function for BlkAioEmAIOCB requests so that
bdrv_aio_cancel() can find the AioContext where the completion BH is
pending. Without this function bdrv_aio_cancel() aborts on ENOMEDIUM
requests!
libFuzzer triggered the following assertion:
cat << EOF | qemu-system-i386 -M pc-q35-5.0 \
-nographic -monitor none -serial none \
-qtest stdio -trace ide\*
outl 0xcf8 0x8000fa24
outl 0xcfc 0xe106c000
outl 0xcf8 0x8000fa04
outw 0xcfc 0x7
outl 0xcf8 0x8000fb20
write 0x0 0x3 0x2780e7
write 0xe106c22c 0xd 0x1130c218021130c218021130c2
write 0xe106c218 0x15 0x110010110010110010110010110010110010110010
EOF
ide_exec_cmd IDE exec cmd: bus 0x56170a77a2b8; state 0x56170a77a340; cmd 0xe7
ide_reset IDEstate 0x56170a77a340
Aborted (core dumped)
(gdb) bt
#1 0x00007ffff4f93895 in abort () at /lib64/libc.so.6
#2 0x0000555555dc6c00 in bdrv_aio_cancel (acb=0x555556765550) at block/io.c:2745
#3 0x0000555555dac202 in blk_aio_cancel (acb=0x555556765550) at block/block-backend.c:1546
#4 0x0000555555b1bd74 in ide_reset (s=0x555557213340) at hw/ide/core.c:1318
#5 0x0000555555b1e3a1 in ide_bus_reset (bus=0x5555572132b8) at hw/ide/core.c:2422
#6 0x0000555555b2aa27 in ahci_reset_port (s=0x55555720eb50, port=2) at hw/ide/ahci.c:650
#7 0x0000555555b29fd7 in ahci_port_write (s=0x55555720eb50, port=2, offset=44, val=16) at hw/ide/ahci.c:360
#8 0x0000555555b2a564 in ahci_mem_write (opaque=0x55555720eb50, addr=556, val=16, size=1) at hw/ide/ahci.c:513
#9 0x000055555598415b in memory_region_write_accessor (mr=0x55555720eb80, addr=556, value=0x7fffffffb838, size=1, shift=0, mask=255, attrs=...) at softmmu/memory.c:483
Looking at bdrv_aio_cancel:
2728 /* async I/Os */
2729
2730 void bdrv_aio_cancel(BlockAIOCB *acb)
2731 {
2732 qemu_aio_ref(acb);
2733 bdrv_aio_cancel_async(acb);
2734 while (acb->refcnt > 1) {
2735 if (acb->aiocb_info->get_aio_context) {
2736 aio_poll(acb->aiocb_info->get_aio_context(acb), true);
2737 } else if (acb->bs) {
2738 /* qemu_aio_ref and qemu_aio_unref are not thread-safe, so
2739 * assert that we're not using an I/O thread. Thread-safe
2740 * code should use bdrv_aio_cancel_async exclusively.
2741 */
2742 assert(bdrv_get_aio_context(acb->bs) == qemu_get_aio_context());
2743 aio_poll(bdrv_get_aio_context(acb->bs), true);
2744 } else {
2745 abort(); <===============
2746 }
2747 }
2748 qemu_aio_unref(acb);
2749 }
Fixes: 02c50efe08736116048d5fc355043080f4d5859c ("block: Add bdrv_aio_cancel_async")
Reported-by: Alexander Bulekov <alxndr@bu.edu>
Buglink: https://bugs.launchpad.net/qemu/+bug/1878255
Originally-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
block/block-backend.c | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/block/block-backend.c b/block/block-backend.c
index 0bf0188133..3a13cb5f0b 100644
--- a/block/block-backend.c
+++ b/block/block-backend.c
@@ -1394,8 +1394,16 @@ typedef struct BlkAioEmAIOCB {
bool has_returned;
} BlkAioEmAIOCB;
+static AioContext *blk_aio_em_aiocb_get_aio_context(BlockAIOCB *acb_)
+{
+ BlkAioEmAIOCB *acb = container_of(acb_, BlkAioEmAIOCB, common);
+
+ return blk_get_aio_context(acb->rwco.blk);
+}
+
static const AIOCBInfo blk_aio_em_aiocb_info = {
.aiocb_size = sizeof(BlkAioEmAIOCB),
+ .get_aio_context = blk_aio_em_aiocb_get_aio_context,
};
static void blk_aio_complete(BlkAioEmAIOCB *acb)
--
2.26.2
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH for-5.1] block: fix bdrv_aio_cancel() for ENOMEDIUM requests
2020-07-20 10:01 [PATCH for-5.1] block: fix bdrv_aio_cancel() for ENOMEDIUM requests Stefan Hajnoczi
@ 2020-07-21 10:01 ` Max Reitz
0 siblings, 0 replies; 2+ messages in thread
From: Max Reitz @ 2020-07-21 10:01 UTC (permalink / raw)
To: Stefan Hajnoczi, qemu-devel
Cc: Kevin Wolf, Alexander Bulekov, qemu-stable, qemu-block,
Philippe Mathieu-Daudé
On 20.07.20 12:01, Stefan Hajnoczi wrote:
> bdrv_aio_cancel() calls aio_poll() on the AioContext for the given I/O
> request until it has completed. ENOMEDIUM requests are special because
> there is no BlockDriverState when the drive has no medium!
>
> Define a .get_aio_context() function for BlkAioEmAIOCB requests so that
> bdrv_aio_cancel() can find the AioContext where the completion BH is
> pending. Without this function bdrv_aio_cancel() aborts on ENOMEDIUM
> requests!
>
> libFuzzer triggered the following assertion:
>
> cat << EOF | qemu-system-i386 -M pc-q35-5.0 \
> -nographic -monitor none -serial none \
> -qtest stdio -trace ide\*
> outl 0xcf8 0x8000fa24
> outl 0xcfc 0xe106c000
> outl 0xcf8 0x8000fa04
> outw 0xcfc 0x7
> outl 0xcf8 0x8000fb20
> write 0x0 0x3 0x2780e7
> write 0xe106c22c 0xd 0x1130c218021130c218021130c2
> write 0xe106c218 0x15 0x110010110010110010110010110010110010110010
> EOF
> ide_exec_cmd IDE exec cmd: bus 0x56170a77a2b8; state 0x56170a77a340; cmd 0xe7
> ide_reset IDEstate 0x56170a77a340
> Aborted (core dumped)
>
> (gdb) bt
> #1 0x00007ffff4f93895 in abort () at /lib64/libc.so.6
> #2 0x0000555555dc6c00 in bdrv_aio_cancel (acb=0x555556765550) at block/io.c:2745
> #3 0x0000555555dac202 in blk_aio_cancel (acb=0x555556765550) at block/block-backend.c:1546
> #4 0x0000555555b1bd74 in ide_reset (s=0x555557213340) at hw/ide/core.c:1318
> #5 0x0000555555b1e3a1 in ide_bus_reset (bus=0x5555572132b8) at hw/ide/core.c:2422
> #6 0x0000555555b2aa27 in ahci_reset_port (s=0x55555720eb50, port=2) at hw/ide/ahci.c:650
> #7 0x0000555555b29fd7 in ahci_port_write (s=0x55555720eb50, port=2, offset=44, val=16) at hw/ide/ahci.c:360
> #8 0x0000555555b2a564 in ahci_mem_write (opaque=0x55555720eb50, addr=556, val=16, size=1) at hw/ide/ahci.c:513
> #9 0x000055555598415b in memory_region_write_accessor (mr=0x55555720eb80, addr=556, value=0x7fffffffb838, size=1, shift=0, mask=255, attrs=...) at softmmu/memory.c:483
>
> Looking at bdrv_aio_cancel:
>
> 2728 /* async I/Os */
> 2729
> 2730 void bdrv_aio_cancel(BlockAIOCB *acb)
> 2731 {
> 2732 qemu_aio_ref(acb);
> 2733 bdrv_aio_cancel_async(acb);
> 2734 while (acb->refcnt > 1) {
> 2735 if (acb->aiocb_info->get_aio_context) {
> 2736 aio_poll(acb->aiocb_info->get_aio_context(acb), true);
> 2737 } else if (acb->bs) {
> 2738 /* qemu_aio_ref and qemu_aio_unref are not thread-safe, so
> 2739 * assert that we're not using an I/O thread. Thread-safe
> 2740 * code should use bdrv_aio_cancel_async exclusively.
> 2741 */
> 2742 assert(bdrv_get_aio_context(acb->bs) == qemu_get_aio_context());
> 2743 aio_poll(bdrv_get_aio_context(acb->bs), true);
> 2744 } else {
> 2745 abort(); <===============
> 2746 }
> 2747 }
> 2748 qemu_aio_unref(acb);
> 2749 }
>
> Fixes: 02c50efe08736116048d5fc355043080f4d5859c ("block: Add bdrv_aio_cancel_async")
> Reported-by: Alexander Bulekov <alxndr@bu.edu>
> Buglink: https://bugs.launchpad.net/qemu/+bug/1878255
> Originally-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
> block/block-backend.c | 8 ++++++++
> 1 file changed, 8 insertions(+)
Thanks, applied to my block branch:
https://git.xanclic.moe/XanClic/qemu/commits/branch/block
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2020-07-20 10:01 [PATCH for-5.1] block: fix bdrv_aio_cancel() for ENOMEDIUM requests Stefan Hajnoczi
2020-07-21 10:01 ` Max Reitz
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