> In packfile.c:1680, there's an infinite loop that tries to get > to the base of a packfile. With offset deltas, the offset needs > to be greater than 0, so it's always walking backwards, and the > search is guaranteed to terminate. > > With reference deltas, there's no check for a cycle in the > references, so a cyclic reference will cause git to loop > infinitely, growing the delta_stack infinitely, which will > cause it to consume all available memory as as a full CPU > core. > > This change puts an arbitrary limit of 10,000 on the number > of iterations we make when chasing down a base commit, to > prevent looping forever, using all available memory growing > the delta stack. For context, I discovered this accidentally when I introduced a bug in pack deltification in git9 (my implementation of git for plan 9). An example of a packfile and index that will reproduce this issue is available here: https://eigenstate.org/tmp/95a0f4f3f3f21d723d501552eaf22ff4055e13a4.pack https://eigenstate.org/tmp/95a0f4f3f3f21d723d501552eaf22ff4055e13a4.idx The suggestion to just cap the depth instead of doing full cycle detection came from Jeff King (peff@xxxxxxxx)
