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Date: Thu, 20 Jun 2019 16:03:45 +0200 From: Jan Kara <jack@...e.cz> To: "Darrick J. Wong" <darrick.wong@...cle.com> Cc: matthew.garrett@...ula.com, yuchao0@...wei.com, tytso@....edu, ard.biesheuvel@...aro.org, josef@...icpanda.com, clm@...com, adilger.kernel@...ger.ca, viro@...iv.linux.org.uk, jack@...e.com, dsterba@...e.com, jaegeuk@...nel.org, jk@...abs.org, reiserfs-devel@...r.kernel.org, linux-efi@...r.kernel.org, devel@...ts.orangefs.org, linux-kernel@...r.kernel.org, linux-f2fs-devel@...ts.sourceforge.net, linux-xfs@...r.kernel.org, linux-mm@...ck.org, linux-nilfs@...r.kernel.org, linux-mtd@...ts.infradead.org, ocfs2-devel@....oracle.com, linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org, linux-btrfs@...r.kernel.org Subject: Re: [PATCH 4/6] vfs: don't allow most setxattr to immutable files On Mon 10-06-19 21:46:45, Darrick J. Wong wrote: > From: Darrick J. Wong <darrick.wong@...cle.com> > > 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@...cle.com> > --- > fs/inode.c | 31 +++++++++++++++++++++++++++++++ > 1 file changed, 31 insertions(+) > > > diff --git a/fs/inode.c b/fs/inode.c > index a3757051fd55..adfb458bf533 100644 > --- a/fs/inode.c > +++ b/fs/inode.c > @@ -2184,6 +2184,17 @@ int vfs_ioc_setflags_check(struct inode *inode, int oldflags, int flags) > !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)) { > + if ((oldflags & ~FS_IMMUTABLE_FL) != > + (flags & ~FS_IMMUTABLE_FL)) This check looks a bit strange when you've just check FS_IMMUTABLE_FL isn't changing... Why not just oldflags != flags? > + if ((old_fa->fsx_xflags & FS_XFLAG_IMMUTABLE) && > + (fa->fsx_xflags & FS_XFLAG_IMMUTABLE)) { > + if ((old_fa->fsx_xflags & ~FS_XFLAG_IMMUTABLE) != > + (fa->fsx_xflags & ~FS_XFLAG_IMMUTABLE)) Ditto here... > + return -EPERM; > + if (old_fa->fsx_projid != fa->fsx_projid) > + return -EPERM; > + if ((fa->fsx_xflags & (FS_XFLAG_EXTSIZE | > + FS_XFLAG_EXTSZINHERIT)) && > + old_fa->fsx_extsize != fa->fsx_extsize) > + return -EPERM; > + if ((old_fa->fsx_xflags & FS_XFLAG_COWEXTSIZE) && > + old_fa->fsx_cowextsize != fa->fsx_cowextsize) > + 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); Honza -- Jan Kara <jack@...e.com> SUSE Labs, CR
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