[OpenWrt-Devel] [PATCH procd 2/4] system: fix failing image validation due to EINTR

[Hauke Mehrtens]

On 1/3/20 1:46 AM, Petr Štetiar wrote:
> It was quite common to see following error during sysupgrade on serial
> console:
> 
>  Failed to parse JSON: 4
> 
> This is happening due to the fact, that validate_firmware_image_call
> fork()s then waits in blocking read() for the input from the child
> process, but child finishes its tasks and exits, thus emitting SIGCHLD
> signal which then leads to the interruption of the blocking read() in
> the parent process with EINTR error.
> 
> It seems like the recent fixes in the libubox library, particulary in
> the jshn sub-component (which empowers json_dump used in the shell
> script executed by the child process) made the execution somehow faster,
> thus exposing this racy behaviour in the validate_firmware_image_call at
> least on RPi-4 (Cortex-A72) target.
> 
> So this patch fixes this issue by checking the read() return value and
> retrying the read() if interrupted due to the EINTR error.
> 
> Ref: http://lists.infradead.org/pipermail/openwrt-devel/2020-January/020994.html
> Fixes: e990e215e8a3 ("system: add "validate_firmware_image" ubus method")
> Cc: Rafał Miłecki <rafal at milecki.pl>
> Reported-by: Petr Novák <petrn at me.com>
> Signed-off-by: Petr Štetiar <ynezz at true.cz>
> ---

Reviewed-by: Hauke Mehrtens <hauke at hauke-m.de>

>  system.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/system.c b/system.c
> index 65d3f09b7fb6..5cd88e0d8227 100644
> --- a/system.c
> +++ b/system.c
> @@ -466,6 +466,9 @@ static int validate_firmware_image_call(const char *file)
>  
>  	blob_buf_init(&b, 0);
>  	while ((len = read(fds[0], buf, sizeof(buf)))) {
> +		if (len < 0 && errno == EINTR)
> +			continue;
> +
>  		jsobj = json_tokener_parse_ex(tok, buf, len);
>  
>  		if (json_tokener_get_error(tok) == json_tokener_success)
> 
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> 


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