| 29 Dec 2025 |
 emily | I just mean it's a disadvantage of setting it | 00:59:29 |
| emily | with your patch, what happens if glib wants to select over more than 4096 fds? does it do the check itself and bail out, or would it trash the heap? | 01:00:21 |
 Ihar Hrachyshka | probably it will trash the heap. like it will do on *BSD or Windows. | 01:01:59 |
| emily | on Windows it has a custom implementation with the native API and on BSD it'll use poll | 01:02:52 |
 Randy Eckenrode | Windows doesn’t use the same implementation. See the Old New Thing article. | 01:03:00 |
| emily | it's only Darwin using this code path, and indeed it doesn't have checks https://gitlab.gnome.org/GNOME/glib/-/blob/ecef4b16cfe1a67f18c82f7b12f58241922c7b89/glib/gpoll.c#L544 | 01:03:00 |
| Ihar Hrachyshka | docs don't promise / mention fd limits: https://docs.gtk.org/glib/func.poll.html | 01:03:07 |
| emily | well it is only select that has this footgun in the first place | 01:03:32 |
| Ihar Hrachyshka | indeed windows uses a different implementation. It uses same macro but ends up with a different code path.. :( | 01:04:41 |
| emily | https://gitlab.gnome.org/GNOME/glib/-/blob/ecef4b16cfe1a67f18c82f7b12f58241922c7b89/glib/gpoll.c#L544 doesn't bother doing any checks, but Darwin's FD_SET will do overflow checks by default (see sys/_types/_fd_def.h), but _DARWIN_UNLIMITED_SELECT adjusts the behaviour | 01:04:43 |
| emily | so I think this turns something likely caught at runtime into a potential vulnerability, on Darwin | 01:05:06 |
| emily | I think what would be ideal is #define _DARWIN_UNLIMITED_SELECT just in this file and doing it as a heap allocation | 01:05:38 |
| Ihar Hrachyshka | ok. should I add an explicit nfds check against SET_FDSIZE in that g_poll implementation? would it save runtime? | 01:06:07 |
| emily | of a struct { int32_t fds_bits[]; } | 01:06:13 |
| emily | yeah that would also work as a cheaper fix | 01:06:40 |
| emily | but it should only be a few lines to do the heap allocation thing | 01:06:45 |
| emily | something like… | 01:08:49 |
