From d80ac658f2caacfb14ea386211c4a9bea0cea280 Mon Sep 17 00:00:00 2001 From: Peter Feiner Date: Wed, 8 Jan 2014 19:43:25 +0000 Subject: block: fix backing file segfault When a backing file is opened such that (1) a protocol is directly used as the block driver and (2) the block driver has bdrv_file_open, bdrv_open_backing_file segfaults. The problem arises because bdrv_open_common returns without setting bd->backing_hd->file. To effect (1), you seem to have to use the -F flag in qemu-img. There are several block drivers that satisfy (2), such as "file" and "nbd". Here are some concrete examples: #!/bin/bash echo Test file format ./qemu-img create -f file base.file 1m ./qemu-img create -f qcow2 -F file -o backing_file=base.file\ file-overlay.qcow2 ./qemu-img convert -O raw file-overlay.qcow2 file-convert.raw echo Test nbd format SOCK=$PWD/nbd.sock ./qemu-img create -f raw base.raw 1m ./qemu-nbd -t -k $SOCK base.raw & trap "kill $!" EXIT while ! test -e $SOCK; do sleep 1; done ./qemu-img create -f qcow2 -F nbd -o backing_file=nbd:unix:$SOCK\ nbd-overlay.qcow2 ./qemu-img convert -O raw nbd-overlay.qcow2 nbd-convert.raw Without this patch, the two qemu-img convert commands segfault. This is a regression that was introduced in v1.7 by dbecebddfa4932d1c83915bcb9b5ba5984eb91be. Signed-off-by: Peter Feiner Reviewed-by: Max Reitz Signed-off-by: Kevin Wolf --- block.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) (limited to 'block.c') diff --git a/block.c b/block.c index 6af5f6e39f..53cc9e09c2 100644 --- a/block.c +++ b/block.c @@ -1040,8 +1040,12 @@ int bdrv_open_backing_file(BlockDriverState *bs, QDict *options, Error **errp) error_free(local_err); return ret; } - pstrcpy(bs->backing_file, sizeof(bs->backing_file), - bs->backing_hd->file->filename); + + if (bs->backing_hd->file) { + pstrcpy(bs->backing_file, sizeof(bs->backing_file), + bs->backing_hd->file->filename); + } + return 0; } -- cgit v1.2.3