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unix: check Fchmodat flags parameter on Linux

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Currently Linux' fchmodat(2) syscall implementation doesn't support the
flags parameter (though it might in future versions [1]). Fchmodat in
x/sys/unix 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

Change the Fchmodat implementation accordingly and also add the
corresponding test.

Fixes golang/go#20130

Change-Id: I62e677e6674d3702eaf388af0ac3d7e623a35c24
Reviewed-on: https://go-review.googlesource.com/46474
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
This commit is contained in:
Tobias Klauser
2017-06-23 14:22:15 +00:00
committed by Ian Lance Taylor
parent fb4cac33e3
commit c23410a886
13 changed files with 205 additions and 166 deletions
Download Patch File Download Diff File Expand all files Collapse all files
unix/syscall_linux.go
+14 -1
View File
@@ -36,6 +36,20 @@ 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 ioctl(fd int, req uint, arg uintptr) (err error)
// ioctl itself should not be exposed directly, but additional get/set
@@ -1177,7 +1191,6 @@ 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)