On Mon, Dec 21, 2015 at 02:18:20PM +0530, Soumya Koduri wrote: > > > On 12/19/2015 01:38 AM, J. Bruce Fields wrote: > >On Fri, Dec 18, 2015 at 10:47:42PM +0530, Soumya Koduri wrote: > >> > >> > >>On 12/18/2015 08:50 PM, J. Bruce Fields wrote: > >>>On Fri, Dec 18, 2015 at 02:13:40PM +0530, Soumya Koduri wrote: > >>>> > >>>> > >>>>On 12/18/2015 06:07 AM, Malahal Naineni wrote: > >>>>>IIRC, permission checks are done in open(). write/read syscalls should > >>>>>NOT do much access checks (at least based on POSIX). This is why once an > >>>>>open is done, you remove permissions for that process, but it should > >>>>>still be able to read/write based on the open flags it did when it > >>>>>opened the file. > >>>>> > >>>>>I don't know all the details of this defect, but gluster seems to be > >>>>>doing what it is supposed to do. > >>>>> > >>>>Right. Thanks for the correction. I assumed the behavior should be > >>>>same for both OPEN+WRITE vs CREATE+WRITE in the below scenario. But > >>>>looks like (from 'man creat') the open() call that creates a > >>>>read-only file may well return a read/write file descriptor, which > >>>>is the reason the following WRITE can succeed. > >>> > >>>I forgot another complication, which is that knsfd actually does a > >>>temporary open before each read or write--I assume that's getting > >>>translated into fuse and gluster open operations? > >>> > >>yes. It is the OPEN done as part of NFS WRITE which fails with > >>EACCESS error (with both NFSv3 and NFSv4 mounts). > > > >Makes sense for v3, but I wouldn't normally expect the extra temporary > >open on v4 WRITEs. Could you share any details? > > > I re-tried the test on v4 mount using Fedora23 machine, acting as > both NFS server and client (Linux#4.2.3-300.fc23.x86_64). Please > find the pkt trace attached. > > 56 07:23:25.567134 ::1 -> ::1 NFS 288 V4 Call > WRITE StateID: 0xf934 Offset: 0 Len: 7 > 57 07:23:25.567233 192.168.122.17 -> 192.168.122.202 GlusterFS 188 > V330 GETXATTR Call > 58 07:23:25.567732 192.168.122.202 -> 192.168.122.17 GlusterFS 112 > V330 GETXATTR Reply (Call In 57) > 59 07:23:25.567881 192.168.122.17 -> 192.168.122.202 GlusterFS 164 > V330 OPEN Call Remind me what kernel version your server is on? --b. > 60 07:23:25.568354 192.168.122.202 -> 192.168.122.17 GlusterFS 116 > V330 OPEN Reply (Call In 59) > 61 07:23:25.568570 ::1 -> ::1 NFS 144 V4 Reply > (Call In 56) WRITE Status: NFS4ERR_ACCESS > > Thanks, > Soumya > > >--b. > > > >> > >> 63 16:59:09.278651000 ::1 -> ::1 NFS 232 V3 WRITE > >>Call, FH: 0x49a35e54 Offset: 0 Len: 7 FILE_SYNC > >> 64 16:59:09.278926000 192.168.122.1 -> 192.168.122.202 GlusterFS > >>164 V330 OPEN Call > >> 65 16:59:09.278937000 192.168.122.1 -> 192.168.122.202 GlusterFS > >>164 [RPC retransmission of #64][TCP Retransmission] V330 OPEN Call > >> 66 16:59:09.279459000 192.168.122.202 -> 192.168.122.1 GlusterFS > >>116 V330 OPEN Reply (Call In 64) > >> 67 16:59:09.279459000 192.168.122.202 -> 192.168.122.1 GlusterFS > >>116 [RPC duplicate of #66][TCP Retransmission] V330 OPEN Reply (Call > >>In 64) > >> 68 16:59:09.279733000 ::1 -> ::1 NFS 212 V3 WRITE > >>Reply (Call In 63) Error: NFS3ERR_ACCES > >> > >> > >>Thanks, > >>Soumya > >> > >>>In which case it might be worth experimenting with NFSv4 or with Jeff > >>>Layton's filehandle-caching patches. Neither's a real fix, but that > >>>could help confirm whether it's the temporary opens that are a problem. > >>> > >>>--b. > >>> > >>>> > >>>>Thanks, > >>>>Soumya > >>>> > >>>> > >>>>>Regards, Malahal. > >>>>> > >>>>>Soumya Koduri [skoduri@xxxxxxxxxx] wrote: > >>>>>>As mentioned by Bruce, GlusterFS doesn't have owner-override rule > >>>>>>except for setattr. > >>>>>> > >>>>>>I did few experiments to check why this test case passes on plain > >>>>>>glusterfs fuse mount & NFS-Ganesha but fails with kernel-NFS. > >>>>>> > >>>>>>NFS-Ganesha (for most of the FSALs) seem to be passing the actual > >>>>>>request credentials to the back-end filesystem only for > >>>>>>CREATE(-like) and UNLINK fops. For all the remaining fops, it does > >>>>>>the access check at its end and then perform the operation with root > >>>>>>credentials. That's the reason WRITE succeeded in your case as > >>>>>>NFS-Ganesha (like kernel-NFS) skipped the access check if the > >>>>>>request caller_uid proved to be the file's owner. > >>>>>> > >>>>>>In case of native GlusterFS FUSE mount, there is no OPEN fop > >>>>>>involved. WRITE is performed on the fd returned by CREATE. And > >>>>>>strangely GlusterFS seem to be doing certain access checks only > >>>>>>during OPEN but not for WRITE (this seems like a bug and probably > >>>>>>needs to be fixed in Gluster). > >>>>>> > >>>>>>Thanks, > >>>>>>Soumya > >>>>>> > >>>>>>On 12/14/2015 10:27 PM, Omar Walid Llorente wrote: > >>>>>>> > >>>>>>>Thank you Bruce, others, for the responses. I send attached a complete > >>>>>>>capture of the issue, including the glusterfs transactions. > >>>>>>> > >>>>>>>Hope this helps to clear where may it be... > >>>>>>> > >>>>>>>Omar > >>>>>>> > >>>>>>>El 10/12/15 a las 15:44, J. Bruce Fields escribió: > >>>>>>>>On Thu, Dec 10, 2015 at 05:59:33PM +0530, Soumya Koduri wrote: > >>>>>>>>> > >>>>>>>>>On 12/10/2015 04:02 PM, Omar Walid Llorente wrote: > >>>>>>>>>>Hi, Jeff, Bruce, finally I got some time to get the capture of the nfs > >>>>>>>>>>packets (you can find them in attached file nfs-problem-nks.pcap.zip). > >>>>>>>>>>Sorry for being so late. > >>>>>>>>>> > >>>>>>>>>>What I did was the following: > >>>>>>>>>> > >>>>>>>>>>1st) Create the RO file: > >>>>>>>>>>cdc@l056:~/prueba-git$ rm -f kk.txt 444.txt; echo "prueba" > 444.txt; > >>>>>>>>>>chmod 444 444.txt; > >>>>>>>>>> > >>>>>>>>>>2nd) Init the capture: > >>>>>>>>>>root@l056:~# tcpdump -i eth2 -w /tmp/nfs.pcap -s 512 port 2049 > >>>>>>>>>>tcpdump: listening on eth2, link-type EN10MB (Ethernet), capture size > >>>>>>>>>>512 bytes > >>>>>>>>>> > >>>>>>>>>GlusterFS protocol is added to wireshark from version 1.8.0 [1]. It > >>>>>>>>>may be helpful to see what GlusterFS operations are being processed > >>>>>>>>>as part of NFS WRITE call (which has failed in this case). > >>>>>>>>> > >>>>>>>>>Could you please try taking the packet trace on the machine where > >>>>>>>>>NFS server is running (without filtering out based on the port > >>>>>>>>>number). > >>>>>>>>> > >>>>>>>>>Also I tried out the same test on Fedora22 machine, but haven't run > >>>>>>>>>into any issue. What are the fuse mount options you have used to > >>>>>>>>>mount gluster volume? > >>>>>>>>Oh, I think this is a simple problem (but maybe hard to fix). The > >>>>>>>>capture shows NFSv3 traffic like: > >>>>>>>> > >>>>>>>> CREATE -> OK > >>>>>>>> SETATTR (mode set to 0400) -> OK > >>>>>>>> WRITE -> NFS3ERR_ACCES > >>>>>>>> > >>>>>>>>That write would succeed locally (because the mode doesn't matter to a > >>>>>>>>local application that already holds the file open). It would fail over > >>>>>>>>NFSv3, which doesn't know about the open--except that there's a hack for > >>>>>>>>this case: NFSv3 servers allow IO operations to ignore the mode, if the > >>>>>>>>operation comes from the owner of the file. NFSv3 clients are then > >>>>>>>>careful to perform necessary access checks on open to ensure that this > >>>>>>>>owner-override rule doesn't grant too many permissions. > >>>>>>>> > >>>>>>>>That allows NFSv3 applications to see behavior that's mostly like a > >>>>>>>>local filesystem, without opening much of a security hole (since the > >>>>>>>>owner could always chmod anyway). > >>>>>>>> > >>>>>>>>So, knfsd is making this special exception--but gluster (which I believe > >>>>>>>>it's exporting in this case, via fuse?)--probably doesn't.... I'm not > >>>>>>>>sure what you can do about that. > >>>>>>>> > >>>>>>>>--b. > >>>>>>> > >>>>>>-- > >>>>>>To unsubscribe from this list: send the line "unsubscribe linux-nfs" in > >>>>>>the body of a message to majordomo@xxxxxxxxxxxxxxx > >>>>>>More majordomo info at http://vger.kernel.org/majordomo-info.html > >>>>>> > >>>>> > >-- > >To unsubscribe from this list: send the line "unsubscribe linux-nfs" in > >the body of a message to majordomo@xxxxxxxxxxxxxxx > >More majordomo info at http://vger.kernel.org/majordomo-info.html > > -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
