> 2022年8月25日 21:49，Zdenek Kabelac <zkabelac@xxxxxxxxxx> 写道： > > Dne 25. 08. 22 v 15:32 Mikulas Patocka napsal(a): >> >> On Thu, 25 Aug 2022, Zdenek Kabelac wrote: >> >>> Since reproducing this issue is rather 'trival' - since creation of simple >>> linear DM device and reloading it with 'self-reference' table line is easy I'd >>> advocate for some simplistic check on kernel side - as such 'crash' can't be >>> even rebooted with SysRQ+B (on my laptop). >>> >>> I guess some 'bitmap/tree' of already visited device during some check might >>> avoid endless loop although it's quite 'ugly' this check needs to happen on >>> 'resume' phase - so the failure here is hard to deal with - still better than >>> this kernel busy loop. >>> >>> Zdenek >> Detecting dm table self-reference is easy, but detecting a loop in the >> dependency graph is complicated and I would't do it. >> >> There is another (more serious) problem - the user can crash the kernel by >> creating deep-enough non-recursive mapping. We do not specify any maximum >> tree depth that is guaranteed to work. Perhaps we should specify such >> depth and audit the code so that this maximum device depth doesn't >> overflow the stack. > > > yep - I'd not mind if there is a total chaining limit enforced on creation side as well. > > Since the 'kernel stack size' is limit - the amount of recursive calls is also limited - so having such limitation exposed on 'creation' time seems like fair path - compared with crashing kernel during chaing processing.... Although I don’t have deep understand to device mapper, I agree that it sounds as a simple and working way to fix. Thanks. Coly Li -- dm-devel mailing list dm-devel@xxxxxxxxxx https://listman.redhat.com/mailman/listinfo/dm-devel
