GNU bug report logs - #8752
cp: fchown called before fchmod, unable to set file mode

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Milan Novak <milan.novak <at> gmail.com>
To: bug-coreutils <at> gnu.org
Subject: cp: fchown called before fchmod, unable to set file mode
Date: Sat, 28 May 2011 15:10:21 +0200

[Message part 1 (text/plain, inline)]

Hello,

I believe that cp uses wrong order of syscalls when applying target file
attributes; fchown(2) is called before fchmod(2).
As a result it looses access to target file and is unable to apply file mode
correctly; error message is as follows
"cp: preserving permissions for `target': Not owner"

The problem arises when -p (preserve attributes) is present and file owner
is different from user doing the copy.

Same operation using cp on hp-ux 11.31 is successfull, since hp-ux cp calls
chmod(2) before chown(2).

Please let me know what do you think about changing order of fchown(2) <=>
fchmod(2).

Kind Regards,
Milan

---

hp <at> mtest:/home/hp/coreutils $ id
uid=1058(hp) gid=20(users) groups=65535(last)
hp <at> mtest:/home/hp/coreutils $ ll source target
target not found
-rwxrwxrwx 1 elzu radia 32 May 20 15:50 source
hp <at> mtest:/home/hp/coreutils $ tusc -o tusc_hpuxcp.out /usr/bin/cp -p source
target; echo $? ; ll source target
0
-rwxrwxrwx 1 elzu radia 32 May 20 15:50 source
-rwxrwxrwx 1 elzu radia 32 May 20 15:50 target
hp <at> mtest:/home/hp/coreutils $ rm -f target

hp <at> mtest:/home/hp/coreutils $ tusc -o tusc_gnucp.out coreutils-8.11/src/cp
-p source target; echo $? ; ll source target
coreutils-8.11/src/cp: preserving permissions for `target': Not owner #>>>>
ERROR
1
-rwxrwxrwx 1 elzu radia 32 May 20 15:50 source
-rwx------ 1 elzu radia 32 May 20 15:50 target #>>> already owned by user
elzu, so chmod executed as user hp fails

hp <at> mtest:/home/hp/coreutils $ coreutils-8.11/src/cp --version | head -1
cp (GNU coreutils) 8.11

hp <at> mtest:/home/hp/coreutils $ uname -a
HP-UX mtest B.11.31 U ia64 2263078376 unlimited-user license

hp <at> mtest:/home/hp/coreutils $ egrep "target|chown|chmod|exit" tusc_*
tusc_hpuxcp.out:stat64("target", 0x7fffeec0)
............................................ ERR#2 ENT
tusc_hpuxcp.out:stat64("target", 0x40021110)
............................................ ERR#2 ENT
tusc_hpuxcp.out:stat64("target", 0x40021110)
............................................ ERR#2 ENT
tusc_hpuxcp.out:access("target", F_OK)
.................................................. ERR#2 ENT
tusc_hpuxcp.out:open("target", O_WRONLY|O_CREAT|O_TRUNC|0x800, 0)
....................... = 6
tusc_hpuxcp.out:utime("target", 0x7fffe5f0)
............................................. = 0
tusc_hpuxcp.out:chmod("target", 0100777)
................................................ = 0
tusc_hpuxcp.out:chown("target", 1021, 1005)
............................................. = 0
tusc_hpuxcp.out:chmod("target", 0100777)
................................................ ERR#1 EPM
tusc_hpuxcp.out:exit(0)
................................................................. WIFE)

tusc_gnucp.out:stat64("target", 0x7fffedf0)
............................................ ERR#2T
tusc_gnucp.out:stat64("target", 0x7fffeac0)
............................................ ERR#2T
tusc_gnucp.out:open("target", O_WRONLY|O_CREAT|O_EXCL|0x800, 0700)
..................... = 5
tusc_gnucp.out:utime("target", 0x7fffe7a8)
............................................. = 0
tusc_gnucp.out:fchown(5, 1021, 1005)
................................................... = 0     #>>> the problem
is HERE, CHOWN goes before CHMOD;
tusc_gnucp.out:fchmod(5, 0100777)
...................................................... ERR#1M     #>>> this
fails, since user hp is not the owner of the file anymore
tusc_gnucp.out:exit(1)
................................................................. WIFEX)

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