overlayfs relies on the filesystem setting DCACHE_OP_HASH or
DCACHE_OP_COMPARE to reject mounting over case-insensitive directories.
Since commit bb9cd9106b22 ("fscrypt: Have filesystems handle their
d_ops"), we set ->d_op through a hook in ->d_lookup, which
means the root dentry won't have them, causing the mount to accidentally
succeed.
In v6.7-rc7, the following sequence will succeed to mount, but any
dentry other than the root dentry will be a "weird" dentry to ovl and
fail with EREMOTE.
mkfs.ext4 -O casefold lower.img
mount -O loop lower.img lower
mount -t overlay -o lowerdir=lower,upperdir=upper,workdir=work ovl /mnt
Mounting on a subdirectory fails, as expected, because DCACHE_OP_HASH
and DCACHE_OP_COMPARE are properly set by ->lookup.
Fix by explicitly rejecting superblocks that allow case-insensitive
dentries.
While there, re-sort the entries to have more descriptive error messages
first.
Fixes: bb9cd9106b22 ("fscrypt: Have filesystems handle their d_ops")
Signed-off-by: Gabriel Krisman Bertazi <krisman@xxxxxxx>
Acked-by: Amir Goldstein <amir73il@xxxxxxxxx>
---
changes since v2:
- Re-sort checks to trigger more descriptive error messages
first (Amir)
- Add code comment (Amir)
---
fs/overlayfs/params.c | 13 ++++++++++---
include/linux/fs.h | 9 +++++++++
2 files changed, 19 insertions(+), 3 deletions(-)
diff --git a/fs/overlayfs/params.c b/fs/overlayfs/params.c
index 3fe2dde1598f..09a4973f26f9 100644
--- a/fs/overlayfs/params.c
+++ b/fs/overlayfs/params.c
@@ -280,12 +280,19 @@ static int ovl_mount_dir_check(struct fs_context *fc, const struct path *path,
{
struct ovl_fs_context *ctx = fc->fs_private;
- if (ovl_dentry_weird(path->dentry))
- return invalfc(fc, "filesystem on %s not supported", name);
-
if (!d_is_dir(path->dentry))
return invalfc(fc, "%s is not a directory", name);
+ /*
+ * Root dentries of case-insensitive filesystems might not have
+ * the dentry operations set, but still be incompatible with
+ * overlayfs. Check explicitly to prevent post-mount failures.
+ */
+ if (sb_has_encoding(path->mnt->mnt_sb))
+ return invalfc(fc, "case-insensitive filesystem on %s not supported", name);
+
+ if (ovl_dentry_weird(path->dentry))
+ return invalfc(fc, "filesystem on %s not supported", name);
/*
* Check whether upper path is read-only here to report failures
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 98b7a7a8c42e..e6667ece5e64 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -3203,6 +3203,15 @@ extern int generic_check_addressable(unsigned, u64);
extern void generic_set_encrypted_ci_d_ops(struct dentry *dentry);
+static inline bool sb_has_encoding(const struct super_block *sb)
+{
+#if IS_ENABLED(CONFIG_UNICODE)
+ return !!sb->s_encoding;
+#else
+ return false;
+#endif
+}
+
int may_setattr(struct mnt_idmap *idmap, struct inode *inode,
unsigned int ia_valid);
int setattr_prepare(struct mnt_idmap *, struct dentry *, struct iattr *);
--
2.43.0
