On Thu, May 28, 2015 at 5:40 PM, Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx> wrote: > On Thu, May 28, 2015 at 5:05 PM, Andreas Grünbacher > <andreas.gruenbacher@xxxxxxxxx> wrote: >> 2015-05-28 22:50 GMT+02:00 Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>: >>> On Thu, May 28, 2015 at 4:33 PM, J. Bruce Fields <bfields@xxxxxxxxxxxx> wrote: >>>> On Fri, Apr 24, 2015 at 01:04:33PM +0200, Andreas Gruenbacher wrote: >>>>> The NFSv4 client sends the server GETATTR requests with different sets of >>>>> requested attributes depending on the situation. The requested set of >>>>> attributes is encoded in a bitmap; the server replies with the set of >>>>> attributes it could return. These bitmaps can be several words wide. The >>>>> bitmap returned by the server is a subset of the bitmap sent by the client. >>>>> >>>>> While decoding the reply, the client tries to verify the reply bitmap: it >>>>> checks if any previous, unexpected attributes are left in the same word of the >>>>> bitmap for each attribute it tries to decode, then it clears the current >>>>> attribute's bit in the bitmap for the next decode function. >>>>> >>>>> The client fails to detect when unexpected attributes are sent after the last >>>>> expected attribute in each word in the bitmap. >>>> >>>> Is it important that the client catch that? >>> >>> Right. What is the actual problem or bug that this patch is trying to >>> fix? Why do we care if a buggy server sends us extra info that we >>> didn't ask for? >> >> I think we do care to correctly decode (and reject) well-formed but illegal >> server replies. In this case, when switching to the next word of a bitmap, the >> client doesn't check if the previous word has been completely "consumed" yet. >> If any attributes are "missed", decoding the attribute values gets out of sync, >> garbage is decoded, and the error may be missed. >> > > We already do this kind of check with the existing code. What's wrong with it? > Actually, you're right, we don't check for the previous word, however fixing that is a question of adding 2 extra checks in decode_getfattr_attrs(), one in decode_getfattr_statfs(), and one in decode_fsinfo(). It shouldn't require a rewrite of the entire nfs4xdr.c. Trond -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
