ovl_ioctl_set_flags() does a capability check using flags, but then the real ioctl double-fetches flags and uses potentially different value.
The "Check the capability before cred override" comment misleading: user can skip this check by presenting benign flags first and then overwriting them to non-benign flags. Just remove the cred override for now, hoping this doesn't cause a regression. The proper solution is to create a new setxflags i_op (patches are in the works). Xfstests don't show a regression. Reported-by: Dmitry Vyukov <[email protected]> Signed-off-by: Miklos Szeredi <[email protected]> --- fs/overlayfs/file.c | 75 ++------------------------------------------- 1 file changed, 3 insertions(+), 72 deletions(-) diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c index efccb7c1f9bc..3cd1590f2030 100644 --- a/fs/overlayfs/file.c +++ b/fs/overlayfs/file.c @@ -541,46 +541,26 @@ static long ovl_real_ioctl(struct file *file, unsigned int cmd, unsigned long arg) { struct fd real; - const struct cred *old_cred; long ret; ret = ovl_real_fdget(file, &real); if (ret) return ret; - old_cred = ovl_override_creds(file_inode(file)->i_sb); ret = security_file_ioctl(real.file, cmd, arg); if (!ret) ret = vfs_ioctl(real.file, cmd, arg); - revert_creds(old_cred); fdput(real); return ret; } -static unsigned int ovl_iflags_to_fsflags(unsigned int iflags) -{ - unsigned int flags = 0; - - if (iflags & S_SYNC) - flags |= FS_SYNC_FL; - if (iflags & S_APPEND) - flags |= FS_APPEND_FL; - if (iflags & S_IMMUTABLE) - flags |= FS_IMMUTABLE_FL; - if (iflags & S_NOATIME) - flags |= FS_NOATIME_FL; - - return flags; -} - static long ovl_ioctl_set_flags(struct file *file, unsigned int cmd, - unsigned long arg, unsigned int flags) + unsigned long arg) { long ret; struct inode *inode = file_inode(file); - unsigned int oldflags; if (!inode_owner_or_capable(inode)) return -EACCES; @@ -591,12 +571,6 @@ static long ovl_ioctl_set_flags(struct file *file, unsigned int cmd, inode_lock(inode); - /* Check the capability before cred override */ - oldflags = ovl_iflags_to_fsflags(READ_ONCE(inode->i_flags)); - ret = vfs_ioc_setflags_prepare(inode, oldflags, flags); - if (ret) - goto unlock; - ret = ovl_maybe_copy_up(file_dentry(file), O_WRONLY); if (ret) goto unlock; @@ -613,46 +587,6 @@ static long ovl_ioctl_set_flags(struct file *file, unsigned int cmd, } -static long ovl_ioctl_set_fsflags(struct file *file, unsigned int cmd, - unsigned long arg) -{ - unsigned int flags; - - if (get_user(flags, (int __user *) arg)) - return -EFAULT; - - return ovl_ioctl_set_flags(file, cmd, arg, flags); -} - -static unsigned int ovl_fsxflags_to_fsflags(unsigned int xflags) -{ - unsigned int flags = 0; - - if (xflags & FS_XFLAG_SYNC) - flags |= FS_SYNC_FL; - if (xflags & FS_XFLAG_APPEND) - flags |= FS_APPEND_FL; - if (xflags & FS_XFLAG_IMMUTABLE) - flags |= FS_IMMUTABLE_FL; - if (xflags & FS_XFLAG_NOATIME) - flags |= FS_NOATIME_FL; - - return flags; -} - -static long ovl_ioctl_set_fsxflags(struct file *file, unsigned int cmd, - unsigned long arg) -{ - struct fsxattr fa; - - memset(&fa, 0, sizeof(fa)); - if (copy_from_user(&fa, (void __user *) arg, sizeof(fa))) - return -EFAULT; - - return ovl_ioctl_set_flags(file, cmd, arg, - ovl_fsxflags_to_fsflags(fa.fsx_xflags)); -} - long ovl_ioctl(struct file *file, unsigned int cmd, unsigned long arg) { long ret; @@ -663,12 +597,9 @@ long ovl_ioctl(struct file *file, unsigned int cmd, unsigned long arg) ret = ovl_real_ioctl(file, cmd, arg); break; - case FS_IOC_SETFLAGS: - ret = ovl_ioctl_set_fsflags(file, cmd, arg); - break; - case FS_IOC_FSSETXATTR: - ret = ovl_ioctl_set_fsxflags(file, cmd, arg); + case FS_IOC_SETFLAGS: + ret = ovl_ioctl_set_flags(file, cmd, arg); break; default: -- 2.26.2
