Horton

glibc qsort() vulnerability

Mats Kindahl <mats@timescale.com>

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From: Mats Kindahl <mats@timescale.com>
To: pgsql-hackers@lists.postgresql.org
Date: 2024-02-06T14:06:26Z
Lists: pgsql-hackers

Commits

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  1. Use new overflow-safe integer comparison functions.

  2. Introduce overflow-safe integer comparison functions.

  3. Replace calls to pg_qsort() with the qsort() macro.

  4. Switch over to using our own qsort() all the time, as has been proposed

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Hi hackers,

There is a bug in glibc's qsort() algorithm that runs the risk of creating
an out-of-bounds error if the comparison function is not transitive, for
example, if subtraction is used so that it can create an overflow.

See
https://packetstormsecurity.com/files/176931/glibc-qsort-Out-Of-Bounds-Read-Write.html

I checked the existing functions in the latest version of Postgres source
code and most are safe, but there were a few ones that could lead to
overflow. I do not know if these can actually lead to problems, but better
safe than sorry, so I created a patch to fix those few cases and add a
comment to one case that was not clear that it could not overflow.

Best wishes,
Mats Kindahl, Timescale