[PATCH 1/2] ext4: refuse encryption when block size > page size

[Alberto Garcia <berto@igalia.com>]

Encryption is not supported when a filesystem's block size is larger
than the page size, and commit 709f0f1f1bf5 ("ext4: add checks for
large folio incompatibilities when BS > PS") added a check to refuse
mounting such a filesystem.

However, it is also possible to enable the "encrypt" feature on a
filesystem that is already mounted (with tune2fs -O encrypt). Once
that happens it won't be possible to mount the filesystem again in
the future, but there is nothing preventing the user from setting an
encryption policy while the filesystem is still mounted.

Fix this by refusing to set an fscrypt context in ext4_set_context()
when the block size is larger than the page size.

Fixes: 709f0f1f1bf5 ("ext4: add checks for large folio incompatibilities when BS > PS")
Cc: stable@vger.kernel.org # v6.19+
Signed-off-by: Alberto Garcia <berto@igalia.com>
---
 fs/ext4/crypto.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/fs/ext4/crypto.c b/fs/ext4/crypto.c
index 1a0fccb084ef..318b2eaea741 100644
--- a/fs/ext4/crypto.c
+++ b/fs/ext4/crypto.c
@@ -156,6 +156,15 @@ static int ext4_set_context(struct inode *inode, const void *ctx, size_t len,
 	if (ext4_test_inode_flag(inode, EXT4_INODE_DAX))
 		return -EOPNOTSUPP;
 
+	/*
+	 * Encryption is not supported when the block size is larger
+	 * than the page size.  This is rejected at mount time by
+	 * ext4_check_large_folio(), and this check here is for the case
+	 * when the 'encrypt' feature is enabled on a mounted filesystem.
+	 */
+	if (inode->i_sb->s_blocksize > PAGE_SIZE)
+		return -EOPNOTSUPP;
+
 	res = ext4_convert_inline_data(inode);
 	if (res)
 		return res;
-- 
2.47.3