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affs_lookup: switch to d_splice_alias()

RFC PATCH In review Al Viro 3 participants 3 messages May 13, 2018 – Oct 30, 2018

Subsystems (2)
VFS Affs file system
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Al Viro

author maintainer
#0 lore raw

RFC PATCH 1/1 affs_lookup: switch to d_splice_alias()

Making something exportable takes more than providing ->s_export_ops. In particular, ->lookup() *MUST* use d_splice_alias() instead of d_add().

Reading Documentation/filesystems/nfs/Exporting would've been a good idea; as it is, exporting AFFS is badly (and exploitably) broken.

Partially-Fixes: ed4433d72394 "fs/affs: make affs exportable"

Signed-off-by Al Viro <[email protected]>
fs/affs/namei.c +5 -6
index 1ed0fa4c4d48..41c5749f4db7 100644
@@ -201,6 +201,7 @@ affs_lookup(struct inode *dir, struct dentry *dentry, unsigned int flags)
 	struct super_block *sb = dir->i_sb;
 	struct buffer_head *bh;
 	struct inode *inode = NULL;
+	struct dentry *res;
 
 	pr_debug("%s(\"%pd\")\n", __func__, dentry);
 

@@ -223,14 +224,12 @@ affs_lookup(struct inode *dir, struct dentry *dentry, unsigned int flags)
 		}
 		affs_brelse(bh);
 		inode = affs_iget(sb, ino);
-		if (IS_ERR(inode)) {
-			affs_unlock_dir(dir);
-			return ERR_CAST(inode);
-		}
 	}
-	d_add(dentry, inode);
+	res = d_splice_alias(inode, dentry);
+	if (!IS_ERR_OR_NULL(res))
+		res->d_fsdata = dentry->d_fsdata;
 	affs_unlock_dir(dir);
-	return NULL;
+	return res;
 }
 
 int
Acked-by on v1 1/1
#1 lore raw
Quoted 9 lines · Al Viro

Making something exportable takes more than providing ->s_export_ops. In particular, ->lookup() *MUST* use d_splice_alias() instead of d_add().

Reading Documentation/filesystems/nfs/Exporting would've been a good idea; as it is, exporting AFFS is badly (and exploitably) broken.

Partially-Fixes: ed4433d72394 "fs/affs: make affs exportable"

Signed-off-by Al Viro <[email protected]>
Acked-by David Sterba <[email protected]>
#2 lore raw
In reply to Al Viro
Quoted 10 lines · On 13 May 2018 at 18:03 Al Viro <[email protected]> wrote:

Making something exportable takes more than providing ->s_export_ops. In particular, ->lookup() *MUST* use d_splice_alias() instead of d_add().

Reading Documentation/filesystems/nfs/Exporting would've been a good idea; as it is, exporting AFFS is badly (and exploitably) broken.

Hi Al,

Could you tell me where Affs is broken ? affs_get_parent() uses d_obtain_alias() and
your patch fixes the lookup. Do you suggest other updates or to mark nfs support experimental in AFFS or
something else ?

(btw, other export functions are
fh_to_dentry using generic_fh_to_dentry()
fh_to_parent using generic_fh_to_parent()
)

Regards,
Fabian