Commit 949055a2 authored Oct 03, 2016 by Marc-André Lureau Committed by Paolo Bonzini Oct 04, 2016

char: use a fixed idx for child muxed chr



mux_chr_update_read_handler() is adding a new mux_cnt each time
mux_chr_update_read_handler() is called, it's not possible to actually
update the "child" chr callbacks that were set previously. This may lead
to crashes if the "child" chr is destroyed:

valgrind x86_64-softmmu/qemu-system-x86_64 -chardev
stdio,mux=on,id=char0 -mon chardev=char0,mode=control,default

when quitting:

==4306== Invalid read of size 8
==4306==    at 0x8061D3: json_lexer_destroy (json-lexer.c:385)
==4306==    by 0x7E39F8: json_message_parser_destroy (json-streamer.c:134)
==4306==    by 0x3447F6: monitor_qmp_event (monitor.c:3908)
==4306==    by 0x480153: mux_chr_send_event (qemu-char.c:630)
==4306==    by 0x480694: mux_chr_event (qemu-char.c:734)
==4306==    by 0x47F1E9: qemu_chr_be_event (qemu-char.c:205)
==4306==    by 0x481207: fd_chr_close (qemu-char.c:1114)
==4306==    by 0x481659: qemu_chr_close_stdio (qemu-char.c:1221)
==4306==    by 0x486F07: qemu_chr_free (qemu-char.c:4146)
==4306==    by 0x486F97: qemu_chr_delete (qemu-char.c:4154)
==4306==    by 0x487E66: qemu_chr_cleanup (qemu-char.c:4678)
==4306==    by 0x495A98: main (vl.c:4675)
==4306==  Address 0x28439e90 is 112 bytes inside a block of size 240 free'd
==4306==    at 0x4C2CD5A: free (vg_replace_malloc.c:530)
==4306==    by 0x1E4CBF2D: g_free (in /usr/lib64/libglib-2.0.so.0.4800.2)
==4306==    by 0x344DE9: monitor_cleanup (monitor.c:4058)
==4306==    by 0x495A93: main (vl.c:4674)
==4306==  Block was alloc'd at
==4306==    at 0x4C2BBAD: malloc (vg_replace_malloc.c:299)
==4306==    by 0x1E4CBE18: g_malloc (in /usr/lib64/libglib-2.0.so.0.4800.2)
==4306==    by 0x344BF8: monitor_init (monitor.c:4021)
==4306==    by 0x49063C: mon_init_func (vl.c:2417)
==4306==    by 0x7FC6DE: qemu_opts_foreach (qemu-option.c:1116)
==4306==    by 0x4954E0: main (vl.c:4473)

Instead, keep the "child" chr associated with a particular idx so its
handlers can be updated and removed to avoid the crash.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20161003094704.18087-3-marcandre.lureau@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

parent 25a85359

include/sysemu/char.h

+1 −0

Original line number	Diff line number	Diff line
		@@ -92,6 +92,7 @@ struct CharDriverState {
		int explicit_be_open;
		int avail_connections;
		int is_mux;
		int mux_idx;
		guint fd_in_tag;
		QemuOpts *opts;
		bool replay;

qemu-char.c

+15 −7

Original line number	Diff line number	Diff line
		@@ -165,6 +165,7 @@ CharDriverState qemu_chr_alloc(ChardevCommon backend, Error **errp)
		CharDriverState *chr = g_malloc0(sizeof(CharDriverState));
		qemu_mutex_init(&chr->chr_write_lock);

		chr->mux_idx = -1;
		if (backend->has_logfile) {
		int flags = O_WRONLY \| O_CREAT;
		if (backend->has_logappend &&
		@@ -738,17 +739,25 @@ static void mux_chr_update_read_handler(CharDriverState *chr,
		GMainContext *context)
		{
		MuxDriver *d = chr->opaque;
		int idx;

		if (d->mux_cnt >= MAX_MUX) {
		fprintf(stderr, "Cannot add I/O handlers, MUX array is full\n");
		return;
		}
		d->ext_opaque[d->mux_cnt] = chr->handler_opaque;
		d->chr_can_read[d->mux_cnt] = chr->chr_can_read;
		d->chr_read[d->mux_cnt] = chr->chr_read;
		d->chr_event[d->mux_cnt] = chr->chr_event;

		if (chr->mux_idx == -1) {
		chr->mux_idx = d->mux_cnt++;
		}

		idx = chr->mux_idx;
		d->ext_opaque[idx] = chr->handler_opaque;
		d->chr_can_read[idx] = chr->chr_can_read;
		d->chr_read[idx] = chr->chr_read;
		d->chr_event[idx] = chr->chr_event;

		/* Fix up the real driver with mux routines */
		if (d->mux_cnt == 0) {
		if (d->mux_cnt == 1) {
		qemu_chr_add_handlers_full(d->drv, mux_chr_can_read,
		mux_chr_read,
		mux_chr_event,
		@@ -757,8 +766,7 @@ static void mux_chr_update_read_handler(CharDriverState *chr,
		if (d->focus != -1) {
		mux_chr_send_event(d, d->focus, CHR_EVENT_MUX_OUT);
		}
		d->focus = d->mux_cnt;
		d->mux_cnt++;
		d->focus = idx;
		mux_chr_send_event(d, d->focus, CHR_EVENT_MUX_IN);
		}