linux-kernel - Re: [PATCH v2 tracing 3/6] tracing: support IPv6 filter predicates

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Date:   Fri, 9 Jun 2023 17:15:46 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Alan Maguire <alan.maguire@...cle.com>
Cc:     mhiramat@...nel.org, corbet@....net, shuah@...nel.org,
        linux-trace-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 tracing 3/6] tracing: support IPv6 filter predicates

On Fri, 9 Jun 2023 17:12:27 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

> > +		while (isalnum(str[i]) || str[i] == ':') {
> > +			switch (str[i]) {
> > +			case ':':
> > +				i++;
> > +				/* mark "::" index by setting gap */
> > +				if (str[i] == ':') {
> > +					gap = index;
> > +					gap_count++;
> > +					i++;
> > +				}
> > +				if (gap_count > 1) {
> > +					parse_error(pe, FILT_ERR_ILLEGAL_FIELD_OP,
> > +						    pos + s);
> > +					goto err_free;
> > +				}
> > +				break;
> > +			default:
> > +				if (sscanf(&str[i], "%hx", &tmp_v6addr[index]) != 1) {
> > +					parse_error(pe, FILT_ERR_ILLEGAL_FIELD_OP,
> > +						    pos + s);
> > +					goto err_free;
> > +				}
> > +				index++;
> > +				while (isalnum(str[i]))
> > +					i++;
> > +				break;

There should also be a lot more checks here where the input coming in is
correct. It also accepted:

 "123456789abcdef0" as "def0", where I expected it to fail.

-- Steve


> > +			}
> > +		}  
> 
> There appears to be no limit to the above loop. I panic'd my machine with:
> 
>  # echo 'saddr_v6 == 0123:4567:89ab:cdef:0123:4567:89ab:cdef:0123:4567:89ab:cdef:0123:4567:89ab:cdef:0123:4567:89ab:cdef:0123:4567:89ab:cdef:0123:4567:89ab:cdef:0123:4567:89ab:cdef' > /sys/kernel/tracing/events/sock/inet_sk_error_report/filter
> 
> -- Steve
> 
> > +		/* The gap_size here represents the number of u16s the "::"
> > +		 * represents; for ::1 the gap size is 7, for feed::face
> > +		 * it is 6, etc.
> > +		 */
> > +		gap_size = 8 - index;
> > +		index = 0;
> > +		for (j = 0; j < 8; ) {
> > +			if (gap_size > 0 && j == gap) {
> > +				j += gap_size;
> > +			} else {
> > +#ifdef __BIG_ENDIAN
> > +				v6addr[j++] = tmp_v6addr[index];
> > +#else
> > +				v6addr[j++] = ((tmp_v6addr[index] & 0xff) << 8) +
> > +					      ((tmp_v6addr[index] & 0xff00) >> 8);
> > +#endif
> > +				index++;
> > +			}
> > +		}
> > +		pred_val = kzalloc(field->size, GFP_KERNEL);
> > +		memcpy(pred_val, v6addr, field->size);
> > +		pred->val = (u64)pred_val;
> > +		pred->fn_num = FILTER_PRED_FN_MEMCMP;
> > +		if (pred->op == OP_NE)
> > +			pred->not = 1;
> > +
> >  	} else if (str[i] == '0' && tolower(str[i + 1]) == 'x' &&
> >  		   field->size > 8) {
> >  		/* For sizes > 8 bytes, we store hex bytes for comparison;