ext4: fix kernel oops caused by spurious casefold flag

If an directory has the a casefold flag set without the casefold
feature set, s_encoding will not be initialized, and this will cause
the kernel to dereference a NULL pointer.  In addition to adding
checks to avoid these kernel oops, attempts to load inodes with the
casefold flag when the casefold feature is not enable will cause the
file system to be declared corrupted.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>

1 files changed, 4 insertions, 3 deletions

diff --git a/fs/ext4/dir.c b/fs/ext4/dir.c
index 86054f31fe4d..9fdd2b269d61 100644
--- a/fs/ext4/dir.c
+++ b/fs/ext4/dir.c
@@ -668,14 +668,15 @@ static int ext4_d_compare(const struct dentry *dentry, unsigned int len,
 			  const char *str, const struct qstr *name)
 {
 	struct qstr qstr = {.name = str, .len = len };
+	struct inode *inode = dentry->d_parent->d_inode;
 
-	if (!IS_CASEFOLDED(dentry->d_parent->d_inode)) {
+	if (!IS_CASEFOLDED(inode) || !EXT4_SB(inode->i_sb)->s_encoding) {
 		if (len != name->len)
 			return -1;
 		return memcmp(str, name->name, len);
 	}
 
-	return ext4_ci_compare(dentry->d_parent->d_inode, name, &qstr, false);
+	return ext4_ci_compare(inode, name, &qstr, false);
 }
 
 static int ext4_d_hash(const struct dentry *dentry, struct qstr *str)
@@ -685,7 +686,7 @@ static int ext4_d_hash(const struct dentry *dentry, struct qstr *str)
 	unsigned char *norm;
 	int len, ret = 0;
 
-	if (!IS_CASEFOLDED(dentry->d_inode))
+	if (!IS_CASEFOLDED(dentry->d_inode) || !um)
 		return 0;
 
 	norm = kmalloc(PATH_MAX, GFP_ATOMIC);