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syscall: check Fchmodat flags parameter on Linux

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As mentioned in #25845, port CL 46474 from golang.org/x/sys/unix to the
syscall package.

Currently Linux' fchmodat(2) syscall implementation doesn't support the
flags parameter (though it might in future versions [1]). Fchmodat in
the syscall package takes the parameter and (wrongly) passes it on to the
syscall which will ignore it.

According to the POSIX.1-2008 manual page [2], AT_SYMLINK_NOFOLLOW is
the only valid value for the flags parameter and EOPNOTSUPP should be
returned in case changing the mode of a symbolic link is not supported
by the underlying system. EINVAL should be returned for any other value
of the flags parameter.

  [1] https://patchwork.kernel.org/patch/9596301/
  [2] http://pubs.opengroup.org/onlinepubs/9699919799/functions/chmod.html

Updates #20130
Updates #25845

Change-Id: I1021dd0e6a4f4cb3557cb1c1b34dd618c378cda6
Reviewed-on: https://go-review.googlesource.com/118658
Reviewed-by: Ian Lance Taylor <iant@golang.org>
This commit is contained in:
Tobias Klauser 2018-06-13 15:54:42 +02:00 • committed by Tobias Klauser
parent 4a778cdf33
commit fb4fb0430b
13 changed files with 242 additions and 166 deletions
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15
src/syscall/syscall_linux.go
View file

@ -35,6 +35,20 @@ func Creat(path string, mode uint32) (fd int, err error) {
return Open(path, O_CREAT|O_WRONLY|O_TRUNC, mode)
}
//sys fchmodat(dirfd int, path string, mode uint32) (err error)
func Fchmodat(dirfd int, path string, mode uint32, flags int) (err error) {
// Linux fchmodat doesn't support the flags parameter. Mimick glibc's behavior
// and check the flags. Otherwise the mode would be applied to the symlink
// destination which is not what the user expects.
if flags&^_AT_SYMLINK_NOFOLLOW != 0 {
return EINVAL
} else if flags&_AT_SYMLINK_NOFOLLOW != 0 {
return EOPNOTSUPP
}
return fchmodat(dirfd, path, mode)
}
//sys linkat(olddirfd int, oldpath string, newdirfd int, newpath string, flags int) (err error)
func Link(oldpath string, newpath string) (err error) {
@ -830,7 +844,6 @@ func Mount(source string, target string, fstype string, flags uintptr, data stri
//sys Fallocate(fd int, mode uint32, off int64, len int64) (err error)
//sys Fchdir(fd int) (err error)
//sys Fchmod(fd int, mode uint32) (err error)
//sys Fchmodat(dirfd int, path string, mode uint32, flags int) (err error)
//sys Fchownat(dirfd int, path string, uid int, gid int, flags int) (err error)
//sys fcntl(fd int, cmd int, arg int) (val int, err error)
//sys Fdatasync(fd int) (err error)