This is a note to let you know that I've just added the patch titled file: fix close_range() for unshare+cloexec to the 5.11-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: file-fix-close_range-for-unshare-cloexec.patch and it can be found in the queue-5.11 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 9b5b872215fe6d1ca6a1ef411f130bd58e269012 Mon Sep 17 00:00:00 2001 From: Christian Brauner <christian.brauner@xxxxxxxxxx> Date: Fri, 2 Apr 2021 10:29:36 +0200 Subject: file: fix close_range() for unshare+cloexec From: Christian Brauner <christian.brauner@xxxxxxxxxx> commit 9b5b872215fe6d1ca6a1ef411f130bd58e269012 upstream. 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@xxxxxxxxxxxxxxxxxxxxxxxxx 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@xxxxxx> Cc: Giuseppe Scrivano <gscrivan@xxxxxxxxxx> Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx> Cc: linux-fsdevel@xxxxxxxxxxxxxxx Cc: stable@xxxxxxxxxxxxxxx Signed-off-by: Christian Brauner <christian.brauner@xxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- fs/file.c | 21 +++++++++++++++++---- 1 file changed, 17 insertions(+), 4 deletions(-) --- 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); } Patches currently in stable-queue which might be from christian.brauner@xxxxxxxxxx are queue-5.11/file-fix-close_range-for-unshare-cloexec.patch