From: Christian Brauner christian.brauner@ubuntu.com

syzbot reported a bug when putting the last reference to a tasks file descriptor table. Debugging this showed we didn't recalculate the current maximum fd number for CLOSE_RANGE_UNSHARE | CLOSE_RANGE_CLOEXEC after we unshared the file descriptors table. So max_fd could exceed the current fdtable maximum causing us to set excessive bits. As a concrete example, let's say the user requested everything from fd 4 to ~0UL to be closed and their current fdtable size is 256 with their highest open fd being 4. With CLOSE_RANGE_UNSHARE the caller will end up with a new fdtable which has room for 64 file descriptors since that is the lowest fdtable size we accept. But now max_fd will still point to 255 and needs to be adjusted. Fix this by retrieving the correct maximum fd value in __range_cloexec().

Reported-by: syzbot+283ce5a46486d6acdbaf@syzkaller.appspotmail.com Fixes: 582f1fb6b721 ("fs, close_range: add flag CLOSE_RANGE_CLOEXEC") Fixes: fec8a6a69103 ("close_range: unshare all fds for CLOSE_RANGE_UNSHARE | CLOSE_RANGE_CLOEXEC") Cc: Christoph Hellwig hch@lst.de Cc: Giuseppe Scrivano gscrivan@redhat.com Cc: Al Viro viro@zeniv.linux.org.uk Cc: linux-fsdevel@vger.kernel.org Cc: stable@vger.kernel.org Signed-off-by: Christian Brauner christian.brauner@ubuntu.com --- fs/file.c | 21 +++++++++++++++++---- 1 file changed, 17 insertions(+), 4 deletions(-)

diff --git a/fs/file.c b/fs/file.c index f3a4bac2cbe9..f633348029a5 100644 --- a/fs/file.c +++ b/fs/file.c @@ -629,17 +629,30 @@ int close_fd(unsigned fd) } EXPORT_SYMBOL(close_fd); /* for ksys_close() */

+/** + * last_fd - return last valid index into fd table + * @cur_fds: files struct + * + * Context: Either rcu read lock or files_lock must be held. + * + * Returns: Last valid index into fdtable. + */ +static inline unsigned last_fd(struct fdtable *fdt) +{ + return fdt->max_fds - 1; +} + static inline void __range_cloexec(struct files_struct *cur_fds, unsigned int fd, unsigned int max_fd) { struct fdtable *fdt;

- if (fd > max_fd) - return; - + /* make sure we're using the correct maximum value */ spin_lock(&cur_fds->file_lock); fdt = files_fdtable(cur_fds); - bitmap_set(fdt->close_on_exec, fd, max_fd - fd + 1); + max_fd = min(last_fd(fdt), max_fd); + if (fd <= max_fd) + bitmap_set(fdt->close_on_exec, fd, max_fd - fd + 1); spin_unlock(&cur_fds->file_lock); }