Would be great if we had some simple reproducer like this in xfstests.
On Tue, Feb 23, 2021 at 12:27 PM Aurélien Aptel <aaptel@xxxxxxxx> wrote:
>
> From: Aurelien Aptel <aaptel@xxxxxxxx>
>
> flock(2)-type locks are advisory, they are not supposed to prevent IO
> if mode would otherwise allow it. From man page:
>
> flock() places advisory locks only; given suitable permissions on a
> file, a process is free to ignore the use of flock() and perform I/O on
> the file.
>
> Simple reproducer:
>
> #include <stdlib.h>
> #include <stdio.h>
> #include <errno.h>
> #include <sys/file.h>
> #include <sys/types.h>
> #include <sys/wait.h>
> #include <unistd.h>
>
> int main(int argc, char** argv)
> {
> const char* fn = argv[1] ? argv[1] : "aaa";
> int fd, status, rc;
> pid_t pid;
>
> fd = open(fn, O_RDWR|O_CREAT, S_IRWXU);
> pid = fork();
>
> if (pid == 0) {
> flock(fd, LOCK_SH);
> exit(0);
> }
>
> waitpid(pid, &status, 0);
> rc = write(fd, "xxx\n", 4);
> if (rc < 0) {
> perror("write");
> return 1;
> }
>
> puts("ok");
> return 0;
> }
>
> If the locks are advisory the write() call is supposed to work
> otherwise we are trying to write with only a read lock (aka shared
> lock) so it fails.
>
> Signed-off-by: Aurelien Aptel <aaptel@xxxxxxxx>
> ---
> fs/cifs/file.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/fs/cifs/file.c b/fs/cifs/file.c
> index 6d001905c8e5..3e351a534720 100644
> --- a/fs/cifs/file.c
> +++ b/fs/cifs/file.c
> @@ -3242,6 +3242,7 @@ cifs_writev(struct kiocb *iocb, struct iov_iter *from)
> struct inode *inode = file->f_mapping->host;
> struct cifsInodeInfo *cinode = CIFS_I(inode);
> struct TCP_Server_Info *server = tlink_tcon(cfile->tlink)->ses->server;
> + struct cifsLockInfo *lock;
> ssize_t rc;
>
> inode_lock(inode);
> @@ -3257,7 +3258,7 @@ cifs_writev(struct kiocb *iocb, struct iov_iter *from)
>
> if (!cifs_find_lock_conflict(cfile, iocb->ki_pos, iov_iter_count(from),
> server->vals->exclusive_lock_type, 0,
> - NULL, CIFS_WRITE_OP))
> + &lock, CIFS_WRITE_OP) || (lock->flags & FL_FLOCK))
> rc = __generic_file_write_iter(iocb, from);
> else
> rc = -EACCES;
> @@ -3975,6 +3976,7 @@ cifs_strict_readv(struct kiocb *iocb, struct iov_iter *to)
> struct cifsFileInfo *cfile = (struct cifsFileInfo *)
> iocb->ki_filp->private_data;
> struct cifs_tcon *tcon = tlink_tcon(cfile->tlink);
> + struct cifsLockInfo *lock;
> int rc = -EACCES;
>
> /*
> @@ -4000,7 +4002,7 @@ cifs_strict_readv(struct kiocb *iocb, struct iov_iter *to)
> down_read(&cinode->lock_sem);
> if (!cifs_find_lock_conflict(cfile, iocb->ki_pos, iov_iter_count(to),
> tcon->ses->server->vals->shared_lock_type,
> - 0, NULL, CIFS_READ_OP))
> + 0, &lock, CIFS_READ_OP) || (lock->flags & FL_FLOCK))
> rc = generic_file_read_iter(iocb, to);
> up_read(&cinode->lock_sem);
> return rc;
> --
> 2.30.0
>
--
Thanks,
Steve
