diff mbox series

[PULL,15/15] qemu-io: Allow larger write zeroes under no fallback

Message ID 20220308014419.3056549-16-eblake@redhat.com (mailing list archive)
State New, archived
Headers show
Series [PULL,01/15] crypto: mandate a hostname when checking x509 creds on a client | expand

Commit Message

Eric Blake March 8, 2022, 1:44 a.m. UTC 
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 <eblake@redhat.com>
Message-Id: <20211203231539.3900865-4-eblake@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
---
 qemu-io-cmds.c | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)
diff mbox series

Patch

diff --git a/qemu-io-cmds.c b/qemu-io-cmds.c
index 954955c12fb9..45a957093369 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;
     }