From 616d374efa23cb699074ea02b301254ad64d224a Mon Sep 17 00:00:00 2001 From: Adam Borowski Date: Wed, 18 Jul 2018 00:08:59 +0200 Subject: [PATCH] btrfs: allow defrag on a file opened read-only that has rw permissions Requiring a read-write descriptor conflicts both ways with exec, returning ETXTBSY whenever you try to defrag a program that's currently being run, or causing intermittent exec failures on a live system being defragged. As defrag doesn't change the file's contents in any way, there's no reason to consider it a rw operation. Thus, let's check only whether the file could have been opened rw. Such access control is still needed as currently defrag can use extra disk space, and might trigger bugs. We return EINVAL when the request is invalid; here it's ok but merely the user has insufficient privileges. Thus, the EPERM return value reflects the error better -- as discussed in the identical case for dedupe. According to codesearch.debian.net, no userspace program distinguishes these values beyond strerror(). Signed-off-by: Adam Borowski Reviewed-by: David Sterba [ fold the EPERM patch from Adam ] Signed-off-by: David Sterba --- fs/btrfs/ioctl.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c index 4482cf35522e..80fe3c654612 100644 --- a/fs/btrfs/ioctl.c +++ b/fs/btrfs/ioctl.c @@ -2928,8 +2928,14 @@ static int btrfs_ioctl_defrag(struct file *file, void __user *argp) ret = btrfs_defrag_root(root); break; case S_IFREG: - if (!(file->f_mode & FMODE_WRITE)) { - ret = -EINVAL; + /* + * Note that this does not check the file descriptor for write + * access. This prevents defragmenting executables that are + * running and allows defrag on files open in read-only mode. + */ + if (!capable(CAP_SYS_ADMIN) && + inode_permission(inode, MAY_WRITE)) { + ret = -EPERM; goto out; }