Re: [PATCH] qemu-ga: Fix a SIGSEGV on guest-set-time command

[Konstantin Kostiuk <kkostiuk@redhat.com>]

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Reviewed-by: Konstantin Kostiuk <kkostiuk@redhat.com>

On Fri, Oct 18, 2024 at 1:14 PM Sunil Nimmagadda <sunil@nimmagadda.net>
wrote:

> qemu-ga on a NetBSD -current VM terminates with a SIGSEGV upon receiving
> 'guest-set-time' command...
>
> Core was generated by `qemu-ga'.
> Program terminated with signal SIGSEGV, Segmentation fault.
> #0  0x000000000cd37a40 in ga_pipe_read_str (fd=fd@entry=0xffffff922a20,
> str=str@entry=0xffffff922a18)
>     at ../qga/commands-posix.c:88
> 88              *str[len] = '\0';
> [Current thread is 1 (process 1112)]
> (gdb) bt
> #0  0x000000000cd37a40 in ga_pipe_read_str (fd=fd@entry=0xffffff922a20,
> str=str@entry=0xffffff922a18)
>     at ../qga/commands-posix.c:88
> #1  0x000000000cd37b60 in ga_run_command (argv=argv@entry=0xffffff922a90,
>     action=action@entry=0xcda34b8 "set hardware clock to system time",
> errp=errp@entry=0xffffff922a70, in_str=0x0)
>     at ../qga/commands-posix.c:164
> #2  0x000000000cd380c4 in qmp_guest_set_time (has_time=<optimized out>,
> time_ns=<optimized out>,
>     errp=errp@entry=0xffffff922ad0) at ../qga/commands-posix.c:304
> #3  0x000000000cd253d8 in qmp_marshal_guest_set_time (args=<optimized
> out>, ret=<optimized out>, errp=0xffffff922b48)
>     at qga/qga-qapi-commands.c:193
> #4  0x000000000cd4e71c in qmp_dispatch (cmds=cmds@entry=0xcdf5b18
> <ga_commands>, request=request@entry=0xf3c711a4b000,
>     allow_oob=allow_oob@entry=false, cur_mon=cur_mon@entry=0x0) at
> ../qapi/qmp-dispatch.c:220
> #5  0x000000000cd36524 in process_event (opaque=0xf3c711a79000,
> obj=0xf3c711a4b000, err=0x0) at ../qga/main.c:677
> #6  0x000000000cd526f0 in json_message_process_token (lexer=lexer@entry=0xf3c711a79018,
> input=0xf3c712072480,
>     type=type@entry=JSON_RCURLY, x=28, y=1) at
> ../qobject/json-streamer.c:99
> #7  0x000000000cd93860 in json_lexer_feed_char (lexer=lexer@entry=0xf3c711a79018,
> ch=125 '}', flush=flush@entry=false)
>     at ../qobject/json-lexer.c:313
> #8  0x000000000cd93a00 in json_lexer_feed (lexer=lexer@entry=0xf3c711a79018,
>
>     buffer=buffer@entry=0xffffff922d10
> "{\"execute\":\"guest-set-time\"}\n", size=<optimized out>)
>     at ../qobject/json-lexer.c:350
> #9  0x000000000cd5290c in json_message_parser_feed (parser=parser@entry=0xf3c711a79000,
>
>     buffer=buffer@entry=0xffffff922d10
> "{\"execute\":\"guest-set-time\"}\n", size=<optimized out>)
>     at ../qobject/json-streamer.c:121
> #10 0x000000000cd361fc in channel_event_cb (condition=<optimized out>,
> data=0xf3c711a79000) at ../qga/main.c:703
> #11 0x000000000cd3710c in ga_channel_client_event (channel=<optimized
> out>, condition=<optimized out>, data=0xf3c711b2d300)
>     at ../qga/channel-posix.c:94
> #12 0x0000f3c7120d9bec in g_main_dispatch () from
> /usr/pkg/lib/libglib-2.0.so.0
> #13 0x0000f3c7120dd25c in g_main_context_iterate_unlocked.constprop ()
> from /usr/pkg/lib/libglib-2.0.so.0
> #14 0x0000f3c7120ddbf0 in g_main_loop_run () from
> /usr/pkg/lib/libglib-2.0.so.0
> #15 0x000000000cda00d8 in run_agent_once (s=0xf3c711a79000) at
> ../qga/main.c:1522
> #16 run_agent (s=0xf3c711a79000) at ../qga/main.c:1559
> #17 main (argc=<optimized out>, argv=<optimized out>) at ../qga/main.c:1671
> (gdb)
>
> The commandline options used on the host machine...
> qemu-system-aarch64 \
>    -machine type=virt,pflash0=rom \
>    -m 8G \
>    -cpu host \
>    -smp 8 \
>    -accel hvf \
>    -device virtio-net-pci,netdev=unet \
>    -device virtio-blk-pci,drive=hd \
>    -drive file=netbsd.qcow2,if=none,id=hd \
>    -netdev user,id=unet,hostfwd=tcp::2223-:22 \
>    -object rng-random,filename=/dev/urandom,id=viornd0 \
>    -device virtio-rng-pci,rng=viornd0 \
>    -serial mon:stdio \
>    -display none \
>    -blockdev
> node-name=rom,driver=file,filename=/opt/homebrew/Cellar/qemu/9.0.2/share/qemu/edk2-aarch64-code.fd,read-only=true
> \
>    -chardev socket,path=/tmp/qga_netbsd.sock,server=on,wait=off,id=qga0 \
>    -device virtio-serial \
>    -device virtconsole,chardev=qga0,name=org.qemu.guest_agent.0
>
> This patch rectifies the operator precedence while assigning the NUL
> terminator.
>
> Signed-off-by: Sunil Nimmagadda <sunil@nimmagadda.net>
>
> diff --git a/qga/commands-posix.c b/qga/commands-posix.c
> index c2bd0b4..bb41fa9 100644
> --- a/qga/commands-posix.c
> +++ b/qga/commands-posix.c
> @@ -85,7 +85,7 @@ static ssize_t ga_pipe_read_str(int fd[2], char **str)
>          *str = g_realloc(*str, len + n + 1);
>          memcpy(*str + len, buf, n);
>          len += n;
> -        *str[len] = '\0';
> +        (*str)[len] = '\0';
>      }
>      close(fd[0]);
>      fd[0] = -1;
>
>

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