From: Eric Blake Date: Fri, 3 Dec 2021 23:15:28 +0000 (-0600) Subject: qemu-io: Allow larger write zeroes under no fallback X-Git-Tag: v7.0.0~57^2 X-Git-Url: https://git.proxmox.com/?a=commitdiff_plain;h=395aecd037dc35d110b8e1e8cc7d20c1082894b5;p=mirror_qemu.git qemu-io: Allow larger write zeroes under no fallback When writing zeroes can fall back to a slow write, permitting an overly large request can become an amplification denial of service attack in triggering a large amount of work from a small request. But the whole point of the no fallback flag is to quickly determine if writing an entire device to zero can be done quickly (such as when it is already known that the device started with zero contents); in those cases, artificially capping things at 2G in qemu-io itself doesn't help us. Signed-off-by: Eric Blake Message-Id: <20211203231539.3900865-4-eblake@redhat.com> Reviewed-by: Vladimir Sementsov-Ogievskiy --- diff --git a/qemu-io-cmds.c b/qemu-io-cmds.c index 954955c12f..45a9570933 100644 --- a/qemu-io-cmds.c +++ b/qemu-io-cmds.c @@ -603,10 +603,6 @@ static int do_co_pwrite_zeroes(BlockBackend *blk, int64_t offset, .done = false, }; - if (bytes > INT_MAX) { - return -ERANGE; - } - co = qemu_coroutine_create(co_pwrite_zeroes_entry, &data); bdrv_coroutine_enter(blk_bs(blk), co); while (!data.done) { @@ -1160,8 +1156,9 @@ static int write_f(BlockBackend *blk, int argc, char **argv) if (count < 0) { print_cvtnum_err(count, argv[optind]); return count; - } else if (count > BDRV_REQUEST_MAX_BYTES) { - printf("length cannot exceed %" PRIu64 ", given %s\n", + } else if (count > BDRV_REQUEST_MAX_BYTES && + !(flags & BDRV_REQ_NO_FALLBACK)) { + printf("length cannot exceed %" PRIu64 " without -n, given %s\n", (uint64_t)BDRV_REQUEST_MAX_BYTES, argv[optind]); return -EINVAL; }