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tracing/filter: Do not allow infix to exceed end of string
While debugging a WARN_ON() for filtering, I found that it is possible for the filter string to be referenced after its end. With the filter: # echo '>' > /sys/kernel/debug/events/ext4/ext4_truncate_exit/filter The filter_parse() function can call infix_get_op() which calls infix_advance() that updates the infix filter pointers for the cnt and tail without checking if the filter is already at the end, which will put the cnt to zero and the tail beyond the end. The loop then calls infix_next() that has ps->infix.cnt--; return ps->infix.string[ps->infix.tail++]; The cnt will now be below zero, and the tail that is returned is already passed the end of the filter string. So far the allocation of the filter string usually has some buffer that is zeroed out, but if the filter string is of the exact size of the allocated buffer there's no guarantee that the charater after the nul terminating character will be zero. Luckily, only root can write to the filter. Cc: stable@vger.kernel.org # 2.6.33+ Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
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@ -1056,6 +1056,9 @@ static void parse_init(struct filter_parse_state *ps,
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static char infix_next(struct filter_parse_state *ps)
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{
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if (!ps->infix.cnt)
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return 0;
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ps->infix.cnt--;
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return ps->infix.string[ps->infix.tail++];
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@ -1071,6 +1074,9 @@ static char infix_peek(struct filter_parse_state *ps)
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static void infix_advance(struct filter_parse_state *ps)
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{
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if (!ps->infix.cnt)
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return;
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ps->infix.cnt--;
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ps->infix.tail++;
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}
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