On Sat, Jan 20, 2018 at 02:36:08AM +0100, Carl Eugen Hoyos wrote: > 2018-01-19 23:42 GMT+01:00 Michael Niedermayer <mich...@niedermayer.cc>: > > On Fri, Jan 19, 2018 at 07:25:43PM +0100, Carl Eugen Hoyos wrote: > >> 2018-01-19 18:51 GMT+01:00 Michael Niedermayer <mich...@niedermayer.cc>: > >> > On Thu, Jan 18, 2018 at 09:28:40PM +0100, Carl Eugen Hoyos wrote: > >> >> Hi! > >> >> > >> >> The probe score for swf files (with uncompressed headers) is currently > >> >> very high after testing a little more than 24bit, attached patch > >> >> reduces the score. > >> > > >> > hmm > >> > the first 24 bits are tested and all but 2 values are rejected > >> > > >> > thats 23 bits that must match > >> > >> Ok. > >> > >> > then 4 values are tested which can be from 1 to 31 bits each > >> > the tests are each either == 0 or != 0 so they are a bit weak > >> > but its at least adding 4 bits that must match and also len > >> > >> I was sure this is not equivalent to four bits on a specific > >> position (but for the patch I assumed a "best case scenario" > >> where this actually were the case). > >> > >> > itself has to be smallish so we could argue that this gets us to > >> > about 28 bits > >> > >> > and then buf[3] is checked to be < 20 > >> > at this point we need about 32bits to be matching, still not huge but > >> > id think this is stronger than what file extensions prove which are > >> > MAX/2 > >> > >> We return MAX/2 for many "initial 32 bits" tests and I believe > >> we made good experience (and for MAX/2 the extension is > >> ignored or do I misremember?) > >> > > > >> > The test is weakened by using 0 / not 0 / ascii as values though > >> > > >> > Have you seen an actual probe failure ? > >> > >> No, I was looking at another issue. > > > > we have many files with wrong extensions, its not uncommon > > Yes, I misremembered how extensions are rated, I actually > wanted to set the return value to "AVPROBE_SCORE_EXTENSION + 1". > Would that be ok?
yes thx [...] -- Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB Democracy is the form of government in which you can choose your dictator
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