On 12/12/2013 07:38 AM, J. Bruce Fields wrote:
On Wed, Dec 11, 2013 at 03:00:22PM +0400, Stanislav Kholmanskikh wrote:
On 12/11/2013 02:16 PM, Stanislav Kholmanskikh wrote:
[cut off]
This patch makes NFS to behave like local file systems.
[cut off]
This patch allows to run generic/193 without any issues with NFSv3.
With NFSv4 generic/193 fails (but with the other issues, which
existed even before the patch).
generic/193 expects that suid/sgid bits are cleared after the file
truncation:
touch file
chown fsgqa:fsgqa file
chmod u+s file
echo 'xyz' > file
ls -l file
su fsgqa -c 'echo > file'
ls -l file
With ext4 (for example), we have expectable results:
-rwSr--r-- 1 fsgqa fsgqa 4 Dec 11 05:21 file
-rw-r--r-- 1 fsgqa fsgqa 1 Dec 11 05:22 file
With NFSv3 as well:
-rwSr--r-- 1 fsgqa fsgqa 4 Dec 11 05:24 file
-rw-r--r-- 1 fsgqa fsgqa 1 Dec 11 05:25 file
But with NFSv4 the bits are not cleared:
-rwSr--r-- 1 fsgqa fsgqa 1 Dec 11 05:19 file
-rwSr--r-- 1 fsgqa fsgqa 1 Dec 11 05:21 file
'echo > file' issues:
open("file", O_WRONLY|O_CREAT|O_TRUNC, 0666)
Can it be because of design differences between NFSv3 and NFSv4?
In the v3 case I'd expect the open O_TRUNC to result in a SETATTR rpc,
in the v4 case an OPEN rpc. Both result in a call to nfsd_setattr,
though I only see nfsd_setattr turning off the SUID/SGID bits in the
chown case. Are you sure it isn't the subsequent write that clears
those bits?
Actually, in the above test script I occasionally swapped positions of
"echo 'xyz' > file" and "chmod u+s file". Of course, chmod should be
after the writing. Sorry.
But here we are:
rm -f file; touch file
chown fsgqa:fsgqa file
echo 'xyz' > file
chmod u+s file
ls -l file
su fsgqa -c 'echo -n > file' # open(O_TRUNC), close()
ls -l file
su fsgqa -c 'echo > file' # open(O_TRUNC), write("\n"), close()
ls -l file
With NFSv3 suid is cleared after write:
-rwSr--r-- 1 fsgqa fsgqa 4 Dec 12 05:24 file
-rwSr--r-- 1 fsgqa fsgqa 0 Dec 12 05:24 file
-rw-r--r-- 1 fsgqa fsgqa 1 Dec 12 05:25 file
With NFSv4 suid is not cleared after write("\n"):
-rwSr--r-- 1 fsgqa fsgqa 4 Dec 12 05:26 file
-rwSr--r-- 1 fsgqa fsgqa 0 Dec 12 05:26 file
-rwSr--r-- 1 fsgqa fsgqa 1 Dec 12 05:27 file
but if we issue "su fsgqa -c 'echo -n b > file'", we will clear it:
-rw-r--r-- 1 fsgqa fsgqa 1 Dec 12 05:28 file
So if "file" is a file on NFSv4:
-rwSr--r-- 1 fsgqa fsgqa 4 Dec 12 05:26 file
and we do:
fd = open(file, O_WRONLY);
then write(fd, "\n", 1) will not clear suid bit, but write(fd, "b", 1)
will do.
With ext4 suid is cleared after open(O_TRUNC):
-rwSr--r-- 1 fsgqa fsgqa 4 Dec 12 05:29 file
-rw-r--r-- 1 fsgqa fsgqa 0 Dec 12 05:29 file
-rw-r--r-- 1 fsgqa fsgqa 1 Dec 12 05:30 file
Execution of (via 'su fsgqa -c ...'):
fd = open("file", O_WRONLY);
close(fd);
if "file" is on ext4 file system and has suid bit on will not clear suid
bit.
Execution of (via 'su fsgqa -c ...'):
fd = open("file", O_WRONLY);
write(fd, "a", 1);
close(fd);
if "file" is on ext4 file system and has suid bit on will clear suid bit.
To conclude:
1. With NFS suid is not cleared after open(O_TRUNC)
This may be solved by addition of ATTR_SIZE handling in nfsd_setattr
(i.e nfsd_sanitize_attrs). Right?
2. NFSv4 treats "\n" on write() specially.
No ideas by the moment.
But looks to me like nfsd_vfs_write (used in both v3 & v4 cases) clears
suid & guid, so I still don't see it.
--b.
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