Ocfs2 devel - Jun 2019 - [PATCH 4/6] vfs: don't allow most setxattr to immutable files

From: Darrick J. Wong <darrick.wong at oracle.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 at oracle.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))
+			return -EPERM;
+	}
+
 	return 0;
 }
 EXPORT_SYMBOL(vfs_ioc_setflags_check);
@@ -2226,6 +2237,26 @@ 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)) {
+		if ((old_fa->fsx_xflags & ~FS_XFLAG_IMMUTABLE) !+		   
(fa->fsx_xflags & ~FS_XFLAG_IMMUTABLE))
+			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);

On Mon 10-06-19 21:46:45, Darrick J. Wong wrote:
> From: Darrick J. Wong <darrick.wong at oracle.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 at oracle.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 at suse.com>
SUSE Labs, CR