Null pointer dereference in rerere.c

Hi,

I just ran into a segmentation fault during a rebase with rerere enabled. Inspecting the core dump with gdb shows:

(gdb) bt #0 0x000055d673375ce0 in do_rerere_one_path (update=0x7fff03c37f30, rr_item=0x55d6746d0b30) at rerere.c:755 #1 do_plain_rerere (fd=3, rr=0x7fff03c37ef0) at rerere.c:853 #2 rerere (flags=flags@entry=0) at rerere.c:918 #3 0x000055d673246b01 in am_resolve (state=0x7fff03c38120) at builtin/am.c:1901 #4 cmd_am (argc=<optimised out>, argv=<optimised out>, prefix=<optimised out>) at builtin/am.c:2394 #5 0x000055d67323f975 in run_builtin (argv=<optimised out>, argc=<optimised out>, p=<optimised out>) at git.c:346 #6 handle_builtin (argc=<optimised out>, argv=<optimised out>) at git.c:554 #7 0x000055d6732405e5 in run_argv (argv=0x7fff03c394a0, argcp=0x7fff03c394ac) at git.c:606 #8 cmd_main (argc=<optimised out>, argv=<optimised out>) at git.c:683 #9 0x000055d67323f64a in main (argc=4, argv=0x7fff03c396f8) at common-main.c:43 (gdb) info locals path = 0x55d6746d08e0 "<file path redacted>" id = 0x55d6746d01e0 rr_dir = 0x55d6746ccb80 variant = <optimised out> path = <optimised out> id = <optimised out> rr_dir = <optimised out> variant = <optimised out> both = <optimised out> vid = <optimised out> path = <optimised out> (gdb) print id $1 = (struct rerere_id *) 0x55d6746d01e0 (gdb) print id->collection $2 = (struct rerere_dir *) 0x55d6746ccb80 (gdb) print id->collection->status $3 = (unsigned char *) 0x0

This is using Git 2.17.1 from the 1:2.17.1-1ubuntu0.1 Ubuntu package. Looking at the diff between v2.17.1 and master for rerere.c it looks like the part of the rerere.c where the null pointer dereference happens has not been touched, so the issue might still be there. Unfortunately I was unable to reproduce the bug; after removing .git/MERGE_RR.lock and restarting the rebase, it completed fine.

Please let me know if there is anything I can do to help diagnose the problem, or whether I should report the bug to Ubuntu instead.

Kind regards,

Ruud van Asseldonk