On Mon, Jul 1, 2019 at 7:31 PM Darrick J. Wong <darrick.wong@xxxxxxxxxx> wrote: > > From: Darrick J. Wong <darrick.wong@xxxxxxxxxx> > > The chattr manpage has this to say about immutable files: > > "A file with the 'i' attribute cannot be modified: it cannot be deleted > or renamed, no link can be created to this file, most of the file's > metadata can not be modified, and the file can not be opened in write > mode." > > However, we don't actually check the immutable flag in the setattr code, > which means that we can update inode flags and project ids and extent > size hints on supposedly immutable files. Therefore, reject setflags > and fssetxattr calls on an immutable file if the file is immutable and > will remain that way. > > Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx> > --- > v2: use memcmp instead of open coding a bunch of checks Thanks, Reviewed-by: Amir Goldstein <amir73il@xxxxxxxxx> > --- > fs/inode.c | 17 +++++++++++++++++ > 1 file changed, 17 insertions(+) > > diff --git a/fs/inode.c b/fs/inode.c > index cf07378e5731..31f694e405fe 100644 > --- a/fs/inode.c > +++ b/fs/inode.c > @@ -2214,6 +2214,14 @@ int vfs_ioc_setflags_prepare(struct inode *inode, unsigned int oldflags, > !capable(CAP_LINUX_IMMUTABLE)) > return -EPERM; > > + /* > + * We aren't allowed to change any other flags if the immutable flag is > + * already set and is not being unset. > + */ > + if ((oldflags & FS_IMMUTABLE_FL) && (flags & FS_IMMUTABLE_FL) && > + oldflags != flags) > + return -EPERM; > + > /* > * Now that we're done checking the new flags, flush all pending IO and > * dirty mappings before setting S_IMMUTABLE on an inode via > @@ -2284,6 +2292,15 @@ int vfs_ioc_fssetxattr_check(struct inode *inode, const struct fsxattr *old_fa, > !(S_ISREG(inode->i_mode) || S_ISDIR(inode->i_mode))) > return -EINVAL; > > + /* > + * We aren't allowed to change any fields if the immutable flag is > + * already set and is not being unset. > + */ > + if ((old_fa->fsx_xflags & FS_XFLAG_IMMUTABLE) && > + (fa->fsx_xflags & FS_XFLAG_IMMUTABLE) && > + memcmp(fa, old_fa, offsetof(struct fsxattr, fsx_pad))) > + return -EPERM; > + > /* Extent size hints of zero turn off the flags. */ > if (fa->fsx_extsize == 0) > fa->fsx_xflags &= ~(FS_XFLAG_EXTSIZE | FS_XFLAG_EXTSZINHERIT);
