Red Hat Bugzilla – Bug 433860
Daemons linked to libdevmapper segfault if they call dm_task_get_deps on task with no deps
Last modified: 2009-01-09 01:02:42 EST
Description of problem: rpc.mountd periodically segfaults, because it is linked to e2fsprogs libraries which call dm_task_get_deps on a task with no info structure. See bz#433857 filed against e2fsprogs. However, even though it is probably the fault of e2fsprogs for not properly checking first, the fact the device-mapper code is linked in to critical system daemons (for which a segfault is unacceptable) means the device-mapper should be fixed as well, to return gracefully instead of segfaulting in this situation. The relevant code is in ioctl/libdm-iface.c line 950: return (struct dm_deps *) (((void *) dmt->dmi.v4) + dmt->dmi.v4->data_start); This will cause a segfault if the dmi.v4 field of dmt is null. Simply changing this to something like (note I have not actually applied and compiled the following change, so please forgive any mistakes) return dmt && dmt->dmi.v4 ? (struct dm_deps *) (((void *) dmt->dmi.v4) + dmt->dmi.v4->data_start) : (struct dm_deps *) 0; should stop the segfaulting, leaving it up to the caller to deal with a null return value. Similar changes to the other nearby routines in the code should also make device-mapper libraries safer and less prone to segfaulting. Version-Release number of selected component (if applicable): device-mapper-libs-1.02.22-1.fc8
I'll think about it. Sometimes a fatal segfault is preferable to a silent failure when the cause is a coding error.
Could you quote the actual segment of e2fsprogs library code that caused this?
Ah - found it in the other bug. Yes, poorly-written code - hard to protect against that. Easy to spot in a code review though. I'll comment on that bug. struct dm_info info; int i; task = dm_task_create(DM_DEVICE_DEPS); if (!task) return 0; dm_task_set_name(task, name); dm_task_run(task); dm_task_get_info(task, &info); if (!info.exists) { dm_task_destroy(task); return 0; } deps = dm_task_get_deps(task);
One thing to notice, though, is that AFTER the fragment I quoted it does check the return value from dm_task_get_deps: deps = dm_task_get_deps(task); if (!deps || deps->count == 0) { dm_task_destroy(task); return 0; } So here is one case where if dm_task_get_deps had returned null instead of segfaulting when passed a task without deps, the caller would have done the right thing.
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