On 03/13/2018 02:17 PM, Eric W. Biederman wrote: > Waiman Long <longman@xxxxxxxxxx> writes: > >> A user can write arbitrary integer values to msgmni and shmmni sysctl >> parameters without getting error, but the actual limit is really >> IPCMNI (32k). This can mislead users as they think they can get a >> value that is not real. >> >> Enforcing the limit by failing the sysctl parameter write, however, >> can break existing user applications. > Which applications examples please. > > I am seeing this patchset late but it looks like a whole lot of changes > to avoid a theoretical possibility. > > Changes that have an impact on more than just the ipc code you are > patching. > > That makes me feel very uncomfortable with these changes. > > Eric This patchset is constructed to address a customer request that there is no easy way to find out the actual usable range of a sysctl parameter. In this particular case, the customer wants to use more than 32k shared memory segments. They can put in a large value into shmmni, but the application didn't work properly because shmmni was internally clamped to 32k without any visible sign that a smaller limit has been imposed. Out of a concern that there might be customers out there setting those sysctl parameters outside of the allowable range without knowing it, just enforcing the right limits may have the undesirable consequence of breaking their existing setup scripts. I don't have concrete example of what customers are doing that, but it won't look good if we wait until the complaints come in. The new code won't affect existing code unless the necessary flag is set. So would you mind elaborating what other impact do you see that will affect other non-IPC code in an undesirable way? Cheers, Longman
