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Thread: Fix infinite loop from setting scram_iterations to INT_MAX

Fix infinite loop from setting scram_iterations to INT_MAX

From
Kevin K Biju
Date:
Hi,

I stumbled upon a problem with the scram_iterations GUC where setting scram_iterations to INT_MAX and then creating a user causes the command to hang indefinitely.

postgres=# SET scram_iterations=2147483647;
SET
postgres=# CREATE ROLE maxscram WITH PASSWORD 'forever';
<hangs>

I looked into the relevant code and found the issue. Each SCRAM iteration after the first is done in a loop with the following condition:

int i;
...
for (i = 2; i <= iterations; i++)
{
    ...
}

For iterations = INT_MAX, the loop will never terminate since the condition is <= and adding 1 to INT_MAX will lead to i wrapping around to INT_MIN.

I've fixed this by modifying the loop condition to be i < iterations. I've attached a patch with the fix. I considered adding a test as well, but since generating a password with a high number of iterations is very time-consuming, I'm not sure if that would be practical.

I also tried adding this to the current CommitFest, but my account hasn't passed the cooldown period yet.

Thanks,
Kevin
Attachment

Re: Fix infinite loop from setting scram_iterations to INT_MAX

From
Richard Guo
Date:
On Sun, Mar 23, 2025 at 10:41 PM Kevin K Biju <kevinkbiju@gmail.com> wrote:
> int i;
> ...
> for (i = 2; i <= iterations; i++)
> {
>     ...
> }
>
> For iterations = INT_MAX, the loop will never terminate since the condition is <= and adding 1 to INT_MAX will lead
toi wrapping around to INT_MIN. 
>
> I've fixed this by modifying the loop condition to be i < iterations. I've attached a patch with the fix. I
consideredadding a test as well, but since generating a password with a high number of iterations is very
time-consuming,I'm not sure if that would be practical. 

Nice catch.  The fix looks good to me.  It seems to me that it's fine
to go without a test case, since the fix is quite straightforward.

Thanks
Richard

Re: Fix infinite loop from setting scram_iterations to INT_MAX

From
Michael Paquier
Date:
On Mon, Mar 24, 2025 at 09:50:36AM +0900, Richard Guo wrote:
> Nice catch.  The fix looks good to me.  It seems to me that it's fine
> to go without a test case, since the fix is quite straightforward.

One could argue about using an injection point to force trick the
iteration loop to be cheaper, but I could not really get excited about
the coverage vs the cycles spent for it..
--
Michael
Attachment

Re: Fix infinite loop from setting scram_iterations to INT_MAX

From
Richard Guo
Date:
On Mon, Mar 24, 2025 at 9:54 AM Michael Paquier <michael@paquier.xyz> wrote:
> On Mon, Mar 24, 2025 at 09:50:36AM +0900, Richard Guo wrote:
> > Nice catch.  The fix looks good to me.  It seems to me that it's fine
> > to go without a test case, since the fix is quite straightforward.
>
> One could argue about using an injection point to force trick the
> iteration loop to be cheaper, but I could not really get excited about
> the coverage vs the cycles spent for it..

Exactly.

Thanks
Richard

Re: Fix infinite loop from setting scram_iterations to INT_MAX

From
Richard Guo
Date:
On Mon, Mar 24, 2025 at 9:59 AM Richard Guo <guofenglinux@gmail.com> wrote:
> On Mon, Mar 24, 2025 at 9:54 AM Michael Paquier <michael@paquier.xyz> wrote:
> > On Mon, Mar 24, 2025 at 09:50:36AM +0900, Richard Guo wrote:
> > > Nice catch.  The fix looks good to me.  It seems to me that it's fine
> > > to go without a test case, since the fix is quite straightforward.

> > One could argue about using an injection point to force trick the
> > iteration loop to be cheaper, but I could not really get excited about
> > the coverage vs the cycles spent for it..

> Exactly.

I plan to go ahead and push Kevin's fix, barring any objections.

Thanks
Richard

Re: Fix infinite loop from setting scram_iterations to INT_MAX

From
Daniel Gustafsson
Date:
> On 26 Mar 2025, at 07:41, Richard Guo <guofenglinux@gmail.com> wrote:

> I plan to go ahead and push Kevin's fix, barring any objections.

Thanks for picking this up, I had missed this thread.

--
Daniel Gustafsson

Re: Fix infinite loop from setting scram_iterations to INT_MAX

From
Michael Paquier
Date:
On Wed, Mar 26, 2025 at 03:41:10PM +0900, Richard Guo wrote:
> I plan to go ahead and push Kevin's fix, barring any objections.

Thanks, Richard.
--
Michael
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