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From: Andrey Borodin <[email protected]>
To: Tom Lane <[email protected]>
Cc: PostgreSQL mailing lists <[email protected]>
Subject: Re: Potential buffer overrun in spell.c's CheckAffix()
Date: Wed, 22 Apr 2026 16:57:26 +0500
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>



> On 21 Apr 2026, at 22:32, Tom Lane <[email protected]> wrote:
> 
> if (Affix->type == FF_SUFFIX)
> {
> + /* protect against buffer overrun */
> + if (len < Affix->replen || len >= 2 * MAXNORMLEN ||
> + len - Affix->replen + findlen >= 2 * MAXNORMLEN)
> + return NULL;
> +
> strcpy(newword, word);
> strcpy(newword + len - Affix->replen, Affix->find);
> if (baselen) /* store length of non-changed part of word */
> @@ -2112,11 +2139,16 @@ CheckAffix(const char *word, size_t len, AFFIX *Affix, int flagflags, char *neww
> }
> else
> {
> + /* protect against buffer overrun */
> + if (len < Affix->replen ||
> + findlen + len - Affix->replen >= 2 * MAXNORMLEN)
> + return NULL;

Is there a reason for an asymmetric check "len >= 2 * MAXNORMLEN ||”?
Both cases seem symmetrical and we could move it out of “if".


> On 22 Apr 2026, at 03:35, Tom Lane <[email protected]> wrote:
> 
> I chose to do this by silently truncating the input before it can
> overrun the buffer, using logic comparable to the existing logic in
> get_nextfield().  Certainly there's at least as good an argument for
> raising an error, but for now let's follow the existing precedent.

Is there a reason not to emit WARNING? The data is obviously suspicious…
Perhaps, there’s a reason, so maybe just document it then.

Both patches look good to me, AFAICT.


Best regards, Andrey Borodin.

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