[PATCH 7.2.y] ext4: don't enable large folios on encrypted inodes

[Alberto Garcia <berto@igalia.com>]

Commit 709f0f1f1bf5 ("ext4: add checks for large folio
incompatibilities when BS > PS") disables large folios at mount time
if the "encrypt" feature is set. However, enabling that feature on a
mounted filesystem circumvents that check, and writing encrypted data
results in a crash:

  BUG: kernel NULL pointer dereference, address: 0000000000000028
  Workqueue: ext4-rsv-conversion ext4_end_io_rsv_work
  RIP: 0010:ext4_finish_bio+0xf7/0x3e0
  Call Trace:
   ext4_release_io_end+0x51/0x110
   ext4_end_io_end+0x4c/0xe0
   ext4_end_io_rsv_work+0xb3/0x100

Fix this by disabling large folios on encrypted inodes, as is
already done for inodes that use data journaling.

This affects all kernels between v6.19 and v7.2, but it is not needed
in v7.3, where the code was significantly refactored.

Fixes: 709f0f1f1bf5 ("ext4: add checks for large folio incompatibilities when BS > PS")
Signed-off-by: Alberto Garcia <berto@igalia.com>
---
This affects all kernels between v6.19 and v7.2 but only the latter is
still maintained, so I think that it only needs to be applied there.

This patch has no upstream equivalent: in v7.3 the code was
significantly refactored and the problem no longer happens, see commit
b4e409c18c79 ("ext4: Remove fs-layer file contents en/decryption
code").

To reproduce the bug:

# mkfs.ext4 /dev/vdb
# mount /dev/vdb /mnt/
# tune2fs -O encrypt /dev/vdb
# mkdir /mnt/foo
# fscrypt setup /mnt
# fscrypt encrypt /mnt/foo/
# head -c 20M /dev/urandom > /mnt/foo/data
# sync
BUG: kernel NULL pointer dereference, address: 0000000000000028
Workqueue: ext4-rsv-conversion ext4_end_io_rsv_work
[...]

 fs/ext4/inode.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index a33629b397b0..32f79f48a9dd 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -5287,7 +5287,8 @@ void ext4_set_inode_mapping_order(struct inode *inode)
 	if (!min_order && !S_ISREG(inode->i_mode))
 		return;
 
-	if (ext4_test_inode_flag(inode, EXT4_INODE_JOURNAL_DATA))
+	if (ext4_test_inode_flag(inode, EXT4_INODE_JOURNAL_DATA) ||
+	    ext4_test_inode_flag(inode, EXT4_INODE_ENCRYPT))
 		max_order = min_order;
 
 	mapping_set_folio_order_range(inode->i_mapping, min_order, max_order);
-- 
2.47.3