(switched to email. Please respond via emailed reply-to-all, not via the
bugzilla web interface).
On Fri, 18 Dec 2009 16:08:29 GMT
[email protected] wrote:
> http://bugzilla.kernel.org/show_bug.cgi?id=14832
>
> Summary: futimens (AT_FDCWD, arg) should fail
> Product: File System
> Version: 2.5
> Platform: All
> OS/Version: Linux
> Tree: Mainline
> Status: NEW
> Severity: normal
> Priority: P1
> Component: Other
> AssignedTo: [email protected]
> ReportedBy: [email protected]
> Regression: No
>
>
> According to POSIX 2008, futimens() shall fail with EBADF if fd is not a valid
> file descriptor. AT_FDCWD, being negative, falls into this category. Yet this
> program mistakenly changes the timestamps of the current directory, then
> aborts:
>
> #include <sys/stat.h>
> #include <fcntl.h>
> #include <errno.h>
> #include <stdlib.h>
> int
> main ()
> {
> if (futimens (AT_FDCWD, NULL) != -1 || errno != EBADF)
> abort ();
> }
>
> Since futimens is a library call on top of utimensat, the fix is to add a
> special case to the utimensat syscall that fails with EBADF if fd is negative
> when path is NULL.
>
Confused.
: long do_utimes(int dfd, char __user *filename, struct timespec *times, int flags)
: {
: int error = -EINVAL;
:
: if (times && (!nsec_valid(times[0].tv_nsec) ||
: !nsec_valid(times[1].tv_nsec))) {
: goto out;
: }
:
: if (flags & ~AT_SYMLINK_NOFOLLOW)
: goto out;
:
: if (filename == NULL && dfd != AT_FDCWD) {
: struct file *file;
:
: if (flags & AT_SYMLINK_NOFOLLOW)
: goto out;
:
: file = fget(dfd);
: error = -EBADF;
: if (!file)
: goto out;
:
afacit, if filename==NULL and dfd==-1 then fget() will return NULL and
the syscall returns -EBAFD.
Your report doesn't tell us what kernel version you're testing. We did
fix a few things ni this area, but it was a long time ago.
According to Andrew Morton on 12/22/2009 3:31 PM:
> Confused.
>
> : long do_utimes(int dfd, char __user *filename, struct timespec *times, int flags)
> : {
> : int error = -EINVAL;
> :
> : if (times && (!nsec_valid(times[0].tv_nsec) ||
> : !nsec_valid(times[1].tv_nsec))) {
> : goto out;
> : }
> :
> : if (flags & ~AT_SYMLINK_NOFOLLOW)
> : goto out;
> :
> : if (filename == NULL && dfd != AT_FDCWD) {
> : struct file *file;
> :
> : if (flags & AT_SYMLINK_NOFOLLOW)
> : goto out;
> :
> : file = fget(dfd);
> : error = -EBADF;
> : if (!file)
> : goto out;
> :
>
> afacit, if filename==NULL and dfd==-1 then fget() will return NULL and
> the syscall returns -EBAFD.
Yes, that's true if dfd==-1. But My complaint was not about dfd==-1, but
about dfd==AT_FDCWD, in which case, this block of code is skipped, and you
end up operating on the current directory ".". My point is that the line:
if (filename == NULL && dfd != AT_FDCWD) {
should probably be:
if (filename == NULL) {
assuming that fget(AT_FDCWD) likewise fails.
>
> Your report doesn't tell us what kernel version you're testing. We did
> fix a few things ni this area, but it was a long time ago.
Yesterday, Ulrich patched glibc to avoid the issue from the library side
of things (I first raised the report against glibc 2 months ago, along
with a proposed patch:
http://sources.redhat.com/bugzilla/show_bug.cgi?id=10992). But there is
still the case of newer kernels and unpatched glibc, where it would also
be nice to patch the kernel. I reproduced the bug on
2.6.31.6-166.fc12.i686, where this test (part of coreutils' configure
script) failed with status 2:
| #include <fcntl.h>
| #include <sys/stat.h>
| #include <unistd.h>
|
| int
| main ()
| {
| struct timespec ts[2] = { { 1, UTIME_OMIT }, { 1, UTIME_NOW } };
| int fd = creat ("conftest.file", 0600);
| struct stat st;
| if (fd < 0) return 1;
| if (futimens (AT_FDCWD, NULL)) return 2;
| if (futimens (fd, ts)) return 3;
| sleep (1);
| ts[0].tv_nsec = UTIME_NOW;
| ts[1].tv_nsec = UTIME_OMIT;
| if (futimens (fd, ts)) return 4;
| if (fstat (fd, &st)) return 5;
| if (st.st_ctime < st.st_atime) return 6;
|
| ;
| return 0;
| }
--
Don't work too hard, make some time for fun as well!
Eric Blake [email protected]
Eric Blake <[email protected]> writes:
>> afacit, if filename==NULL and dfd==-1 then fget() will return NULL and
>> the syscall returns -EBAFD.
>
> Yes, that's true if dfd==-1. But My complaint was not about dfd==-1, but
> about dfd==AT_FDCWD, in which case, this block of code is skipped, and you
> end up operating on the current directory ".". My point is that the line:
> if (filename == NULL && dfd != AT_FDCWD) {
> should probably be:
> if (filename == NULL) {
> assuming that fget(AT_FDCWD) likewise fails.
No, it changes utimensat() behavior. If error was EBADF, it seems fd
shouldn't be AT_FDCWD. So, this behavior would be right thing as
utimensat().
[EBADF] The path argument does not specify an absolute path and the fd
argument is neither AT_FDCWD nor a valid file descriptor open for
reading or searching.
>> Your report doesn't tell us what kernel version you're testing. We did
>> fix a few things ni this area, but it was a long time ago.
>
> Yesterday, Ulrich patched glibc to avoid the issue from the library side
> of things (I first raised the report against glibc 2 months ago, along
> with a proposed patch:
> http://sources.redhat.com/bugzilla/show_bug.cgi?id=10992). But there is
> still the case of newer kernels and unpatched glibc, where it would also
> be nice to patch the kernel. I reproduced the bug on
> 2.6.31.6-166.fc12.i686, where this test (part of coreutils' configure
> script) failed with status 2:
--
OGAWA Hirofumi <[email protected]>