Re: Fwd: tmpfs inode leakage when opening file with O_TMP_FILE

[Hugh Dickins <hughd@google.com>]

On Tue, 12 Feb 2019, Matej Kupljen wrote:

> Hi all,
> 
> I sent this mail yesterday to kernel mailing list, but I got no reply.
> So, I checked the MAINTAINERS file and I have found these emails.
> I hope this is the right address for this issue.

Yes, thanks: I'll look into it (not this moment),
and reply to you and both lists when I've got something.

Hugh

> 
> Thanks and BR,
> Matej
> 
> ---------- Forwarded message ---------
> From: Matej Kupljen <matej.kupljen@gmail.com>
> Date: Mon, Feb 11, 2019 at 3:18 PM
> Subject: tmpfs inode leakage when opening file with O_TMP_FILE
> To: <linux-kernel@vger.kernel.org>
> 
> 
> Hi,
> 
> it seems that when opening file on file system that is mounted on
> tmpfs with the O_TMPFILE flag and using linkat call after that, it
> uses 2 inodes instead of 1.
> 
> This is simple test case:
> 
> #include <sys/types.h>
> #include <sys/stat.h>
> #include <fcntl.h>
> #include <unistd.h>
> #include <string.h>
> #include <stdio.h>
> #include <stdlib.h>
> #include <linux/limits.h>
> #include <errno.h>
> 
> #define TEST_STRING     "Testing\n"
> 
> #define TMP_PATH        "/tmp/ping/"
> #define TMP_FILE        "file.txt"
> 
> 
> int main(int argc, char* argv[])
> {
>         char path[PATH_MAX];
>         int fd;
>         int rc;
> 
>         fd = open(TMP_PATH, __O_TMPFILE | O_RDWR,
>                         S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP |
> S_IROTH | S_IWOTH);
> 
>         rc = write(fd, TEST_STRING, strlen(TEST_STRING));
> 
>         snprintf(path, PATH_MAX,  "/proc/self/fd/%d", fd);
>         linkat(AT_FDCWD, path, AT_FDCWD, TMP_PATH TMP_FILE, AT_SYMLINK_FOLLOW);
>         close(fd);
> 
>         return 0;
> }
> 
> I have checked indoes with "df -i" tool. The first inode is used when
> the call to open is executed and the second one when the call to
> linkat is executed.
> It is not decreased when close is executed.
> 
> I have also tested this on an ext4 mounted fs and there only one inode is used.
> 
> I tested this on:
> $ cat /etc/lsb-release
> DISTRIB_ID=Ubuntu
> DISTRIB_RELEASE=18.04
> DISTRIB_CODENAME=bionic
> DISTRIB_DESCRIPTION="Ubuntu 18.04.1 LTS"
> 
> $ uname -a
> Linux Orion 4.15.0-43-generic #46-Ubuntu SMP Thu Dec 6 14:45:28 UTC
> 2018 x86_64 x86_64 x86_64 GNU/Linux
> 
> If you need any more information, please let me know.
> 
> And please CC me when replying, I am not subscribed to the list.
> 
> Thanks and BR,
> Matej
>