Currently when passing a closed file descriptor to
fcntl(fd, F_DUPFD_QUERY, fd_dup) the order matters:
fd = open("/dev/null");
fd_dup = dup(fd);
When we now close one of the file descriptors we get:
(1) fcntl(fd, fd_dup) // -EBADF
(2) fcntl(fd_dup, fd) // 0 aka not equal
depending on which file descriptor is passed first. That's not a huge
deal but it gives the api I slightly weird feel. Make it so that the
order doesn't matter by requiring that both file descriptors are valid:
(1') fcntl(fd, fd_dup) // -EBADF
(2') fcntl(fd_dup, fd) // -EBADF
Link: https://lore.kernel.org/r/20241008-duften-formel-251f967602d5@brauner
Fixes: c62b758bae6a ("fcntl: add F_DUPFD_QUERY fcntl()")
Reviewed-by: Jeff Layton <jlayton@xxxxxxxxxx>
Reviewed-By: Lennart Poettering <lennart@xxxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Reported-by: Lennart Poettering <lennart@xxxxxxxxxxxxxx>
Signed-off-by: Christian Brauner <brauner@xxxxxxxxxx>
diff --git a/fs/fcntl.c b/fs/fcntl.c
index 22dd9dcce7ec..3d89de31066a 100644
--- a/fs/fcntl.c
+++ b/fs/fcntl.c
@@ -397,6 +397,9 @@ static long f_dupfd_query(int fd, struct file *filp)
{
CLASS(fd_raw, f)(fd);
+ if (fd_empty(f))
+ return -EBADF;
+
/*
* We can do the 'fdput()' immediately, as the only thing that
* matters is the pointer value which isn't changed by the fdput.
