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Re: [PATCH 1/3] lib/regexec: Fix possible null-dereference

From: Paul Eggert
Subject: Re: [PATCH 1/3] lib/regexec: Fix possible null-dereference
Date: Mon, 23 Aug 2021 13:09:18 -0700
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0

On 8/23/21 3:05 AM, Darren Kenny wrote:

The explanation given by Coverity boils down to:

- In check_matching(), line 1069, there is a test if mctx->state_log !=

This line number doesn't match either the current Gnulib version (commit d3837928885e91c9ddd465240b90a97aa342fda6) nor the version in the current Grub release (2.06). So I guess you are using some other version of regexec.c. Could you tell us which one?

- In transit_state(), there is a call to transit_state_mb() at line
   2226, which in turn, at line 2497, directly references mctx->state_log
   without first checking if it is NULL.

In the Gnulib version, transit_state calls transit_state_mb only if state->accept_mb is true, and if the state can accept multibyte characters then in re_search_internal dfa->has_mb_node must be true, which means that re_search_internal initializes mctx.state_log to a nonnull pointer before we get to transit_state.

So I'm not seeing a bug here; it still appears to be a false alarm. If I'm missing something please let us know.

The patch we have already satisfies Coverity, once applied

Yes, I can see why the patch would pacify Coverity. However, we shouldn't add unnecessary code merely to pacify a Coverity false alarm.

I have not checked if a DEBUG_ASSERT() call, in a path that Coverity isn't
including anywhere in its analysis would work.

Why do you think an assert in clean_state_log_if_needed() would help?

If you tell Coverity to analyze with -DDEBUG, then adding DEBUG_ASSERT (X != NULL) should tell Coverity that X must be nonnull at that point. We can use this method to tell Coverity things that it can't deduce on its own.

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