[{"id":3677294,"web_url":"http://patchwork.ozlabs.org/comment/3677294/","msgid":"<87bjflzgcl.fsf@suse.de>","list_archive_url":null,"date":"2026-04-14T15:55:38","subject":"Re: [PATCH v3 3/4] migration/file: fix type mismatch and NULL deref\n in multifd_file_recv_data","submitter":{"id":85343,"url":"http://patchwork.ozlabs.org/api/people/85343/","name":"Fabiano Rosas","email":"farosas@suse.de"},"content":"Junjie Cao writes:\n\n> multifd_file_recv_data() stores the return value of qio_channel_pread()\n> (ssize_t) in a size_t variable. On I/O error the -1 return value wraps\n> to SIZE_MAX, producing a nonsensical read size in the error message.\n>\n> More critically, a short read (0 <= ret < data->size) is possible when\n> the migration file is truncated. In that case qio_channel_pread()\n> returns a non-negative value without setting *errp. The function then\n> calls error_prepend(errp, ...) which dereferences *errp -- a NULL\n> pointer -- crashing QEMU.\n>\n> Fix both issues by switching to qio_channel_pread_all() introduced in\n> a previous patch, which retries on short reads and treats end-of-file\n> as an error, so the caller no longer needs to check the byte count\n> manually. Add ERRP_GUARD() so that error_prepend() works correctly\n> even when errp is &error_fatal or NULL.\n>\n> Fixes: a49d15a38d3d (\"migration/multifd: Support incoming mapped-ram stream format\")\n> Suggested-by: Peter Xu \n> Reviewed-by: Daniel P. Berrangé \n> Signed-off-by: Junjie Cao \n> ---\n> migration/file.c | 13 +++++++------\n> 1 file changed, 7 insertions(+), 6 deletions(-)\n>\n> diff --git a/migration/file.c b/migration/file.c\n> index 5618aced49..0853188601 100644\n> --- a/migration/file.c\n> +++ b/migration/file.c\n> @@ -254,15 +254,16 @@ int file_write_ramblock_iov(QIOChannel *ioc, const struct iovec *iov,\n> \n> int multifd_file_recv_data(MultiFDRecvParams *p, Error **errp)\n> {\n> + ERRP_GUARD();\n> MultiFDRecvData *data = p->data;\n> - size_t ret;\n> + int ret;\n> \n> - ret = qio_channel_pread(p->c, (char *) data->opaque,\n> - data->size, data->file_offset, errp);\n> - if (ret != data->size) {\n> + ret = qio_channel_pread_all(p->c, (char *) data->opaque,\n> + data->size, data->file_offset, errp);\n> + if (ret != 0) {\n> error_prepend(errp,\n> - \"multifd recv (%u): read 0x%zx, expected 0x%zx\",\n> - p->id, ret, data->size);\n> + \"multifd recv (%u): \",\n> + p->id);\n> return -1;\n> }\n\nReviewed-by: Fabiano Rosas ","headers":{"Return-Path":"","X-Original-To":"incoming@patchwork.ozlabs.org","Delivered-To":"patchwork-incoming@legolas.ozlabs.org","Authentication-Results":["legolas.ozlabs.org;\n\tdkim=pass (1024-bit key;\n unprotected) header.d=suse.de header.i=@suse.de header.a=rsa-sha256\n header.s=susede2_rsa header.b=AnC7GNjN;\n\tdkim=pass header.d=suse.de header.i=@suse.de header.a=ed25519-sha256\n header.s=susede2_ed25519 header.b=SKVBCgyz;\n\tdkim=pass (1024-bit key) header.d=suse.de header.i=@suse.de\n header.a=rsa-sha256 header.s=susede2_rsa header.b=geiy6f9D;\n\tdkim=neutral header.d=suse.de header.i=@suse.de header.a=ed25519-sha256\n header.s=susede2_ed25519 header.b=3cDhn4tE;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=nongnu.org\n (client-ip=209.51.188.17; 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a=ed25519-sha256; c=relaxed/relaxed; d=suse.de;\n s=susede2_ed25519; t=1776182140;\n h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc:\n mime-version:mime-version:content-type:content-type:\n content-transfer-encoding:content-transfer-encoding:\n in-reply-to:in-reply-to:references:references;\n bh=q/F7uWvi3bthbbBDE9JWB6OLCf7YS/XHKddRZk2HtiA=;\n b=3cDhn4tEQquMBiGPRXLB2iMLGSwZpQx5tQBrZfQp1HabBzTWoCrdu4xKLnfuUfbTKSyp6/\n 4Zz+BPcmxpj3EdCw=="],"From":"Fabiano Rosas ","To":"Junjie Cao , qemu-devel@nongnu.org","Cc":"berrange@redhat.com, peterx@redhat.com, junjie.cao@intel.com","Subject":"Re: [PATCH v3 3/4] migration/file: fix type mismatch and NULL deref\n in multifd_file_recv_data","In-Reply-To":"<20260413214549.926435-4-junjie.cao@intel.com>","References":"<20260413214549.926435-1-junjie.cao@intel.com>\n <20260413214549.926435-4-junjie.cao@intel.com>","Date":"Tue, 14 Apr 2026 12:55:38 -0300","Message-ID":"<87bjflzgcl.fsf@suse.de>","MIME-Version":"1.0","Content-Type":"text/plain; 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