STINNER Victor <vstin...@redhat.com> added the comment:
Alexey Izbyshev: "I think that we can even drop dup-based validation from
is_valid_fd() since there is a corner case for Linux too: if a descriptor
opened with O_PATH inherited as a standard one, dup() will succeed but fstat()
will fail in kernels before 3.6. And we do fstat() almost immediately after
is_valid_fd() to get blksize, so the dup-based optimization doesn't seem worth
the trouble. Victor, do you have an opinion on that?"
I don't understand this case. I don't know O_PATH nor how to inherit such
special file descriptor. Would you mind to elaborate?
man open:
O_PATH (since Linux 2.6.39)
Obtain a file descriptor that can be used for two purposes: to
indicate a location in the filesystem tree and to perform opera‐
tions that act purely at the file descriptor level. The file
itself is not opened, and other file operations (e.g., read(2),
write(2), fchmod(2), fchown(2), fgetxattr(2), ioctl(2), mmap(2))
fail with the error EBADF.
In following C program, fd 0 is a file descriptor opened by O_PATH: dup(0) and
fstat(0) both succeed, which is not surprising, it's a valid file descriptor.
---
#include <fcntl.h>
#include <stdio.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>
#define O_PATH 010000000
int main(void)
{
int path_fd;
path_fd = open(".", O_PATH);
if (dup2(path_fd, 0)) {
perror("dup2");
}
int fd = dup(0);
if (fd < 0)
perror("dup");
else {
fprintf(stderr, "dup ok: %d\n", fd);
close(fd);
}
struct stat st;
if (fstat(0, &st) < 0) {
perror("fstat");
}
else {
printf("fstat ok\n");
}
return 0;
}
---
----------
_______________________________________
Python tracker <rep...@bugs.python.org>
<https://bugs.python.org/issue32849>
_______________________________________
_______________________________________________
Python-bugs-list mailing list
Unsubscribe:
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
