[PATCH] fs/ext4: Prevent encryption/decryption of unaligned blocks in aes_encrypt

[Norbert Kamiński]

syzbot is reporting an uninitialized value in aes_encrypt(). The block
cipher expects the bytes to encrypt or decrypt to be a multiple of the
cipher’s block size. However, when ext4_write_begin() is called and new
folios are allocated, they might not be aligned to the required block
size.

To ensure that padding bytes are automatically initialized in the
ext4_write_begin, this patch adds __GFP_ZERO to the existing GFP masks.
This adjustment is applied only when the CONFIG_FS_ENCRYPTION is
defined.

Syzbot reported:

=====================================================
BUG: KMSAN: uninit-value in subshift lib/crypto/aes.c:149 [inline]
BUG: KMSAN: uninit-value in aes_encrypt+0x15cc/0x1db0 lib/crypto/aes.c:282
 subshift lib/crypto/aes.c:149 [inline]
 aes_encrypt+0x15cc/0x1db0 lib/crypto/aes.c:282
 aesti_encrypt+0x7d/0xf0 crypto/aes_ti.c:31
 crypto_ecb_crypt crypto/ecb.c:23 [inline]
 crypto_ecb_encrypt2+0x18a/0x300 crypto/ecb.c:40
 crypto_lskcipher_crypt_sg+0x36b/0x7f0 crypto/lskcipher.c:228
 crypto_lskcipher_encrypt_sg+0x8a/0xc0 crypto/lskcipher.c:247
 crypto_skcipher_encrypt+0x119/0x1e0 crypto/skcipher.c:669
 xts_encrypt+0x3c4/0x550 crypto/xts.c:269
 crypto_skcipher_encrypt+0x1a0/0x1e0 crypto/skcipher.c:671
 fscrypt_crypt_data_unit+0x4ee/0x8f0 fs/crypto/crypto.c:144
 fscrypt_encrypt_pagecache_blocks+0x422/0x900 fs/crypto/crypto.c:207
 ext4_bio_write_folio+0x13db/0x2e40 fs/ext4/page-io.c:526
 mpage_submit_folio+0x351/0x4a0 fs/ext4/inode.c:1869
 mpage_process_page_bufs+0xb92/0xe30 fs/ext4/inode.c:1982
 mpage_prepare_extent_to_map+0x1702/0x22c0 fs/ext4/inode.c:2490
 ext4_do_writepages+0x1117/0x62e0 fs/ext4/inode.c:2632
 ext4_writepages+0x312/0x830 fs/ext4/inode.c:2768
 do_writepages+0x427/0xc30 mm/page-writeback.c:2612
 filemap_fdatawrite_wbc+0x1d8/0x270 mm/filemap.c:397
 __filemap_fdatawrite_range mm/filemap.c:430 [inline]
 file_write_and_wait_range+0x1bf/0x370 mm/filemap.c:788
 generic_buffers_fsync_noflush+0x84/0x3e0 fs/buffer.c:602
 ext4_fsync_nojournal fs/ext4/fsync.c:88 [inline]
 ext4_sync_file+0x5ba/0x13a0 fs/ext4/fsync.c:151
 vfs_fsync_range+0x20d/0x270 fs/sync.c:188
 generic_write_sync include/linux/fs.h:2795 [inline]
 ext4_buffered_write_iter+0x9ad/0xaa0 fs/ext4/file.c:305
 ext4_file_write_iter+0x208/0x3450
 call_write_iter include/linux/fs.h:2110 [inline]
 new_sync_write fs/read_write.c:497 [inline]
 vfs_write+0xb63/0x1520 fs/read_write.c:590
 ksys_write+0x20f/0x4c0 fs/read_write.c:643
 __do_sys_write fs/read_write.c:655 [inline]
 __se_sys_write fs/read_write.c:652 [inline]
 __x64_sys_write+0x93/0xe0 fs/read_write.c:652
 x64_sys_call+0x3062/0x3b50 arch/x86/include/generated/asm/syscalls_64.h:2
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xcf/0x1e0 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Uninit was created at:
 __alloc_pages+0x9d6/0xe70 mm/page_alloc.c:4598
 alloc_pages_mpol+0x299/0x990 mm/mempolicy.c:2264
 alloc_pages mm/mempolicy.c:2335 [inline]
 folio_alloc+0x1d0/0x230 mm/mempolicy.c:2342
 filemap_alloc_folio+0xa6/0x440 mm/filemap.c:984
 __filemap_get_folio+0xa10/0x14b0 mm/filemap.c:1926
 ext4_write_begin+0x3e5/0x2230 fs/ext4/inode.c:1159
 generic_perform_write+0x400/0xc60 mm/filemap.c:3974
 ext4_buffered_write_iter+0x564/0xaa0 fs/ext4/file.c:299
 ext4_file_write_iter+0x208/0x3450
 call_write_iter include/linux/fs.h:2110 [inline]
 new_sync_write fs/read_write.c:497 [inline]
 vfs_write+0xb63/0x1520 fs/read_write.c:590
 ksys_write+0x20f/0x4c0 fs/read_write.c:643
 __do_sys_write fs/read_write.c:655 [inline]
 __se_sys_write fs/read_write.c:652 [inline]
 __x64_sys_write+0x93/0xe0 fs/read_write.c:652
 x64_sys_call+0x3062/0x3b50 arch/x86/include/generated/asm/syscalls_64.h:2
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xcf/0x1e0 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
=====================================================

Reported-by: syzbot+aeb14e2539ffb6d21130@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=aeb14e2539ffb6d21130
Signed-off-by: Norbert Kamiński <norbert.kaminski@xxxxxxxxxxxx>
---
 fs/ext4/inode.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 4bae9ccf5fe0..965f790a9d36 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -1156,6 +1156,9 @@ static int ext4_write_begin(struct file *file, struct address_space *mapping,
 	 * the folio (if needed) without using GFP_NOFS.
 	 */
 retry_grab:
+	if (IS_ENABLED(CONFIG_FS_ENCRYPTION))
+		mapping_set_gfp_mask(mapping,
+				     mapping_gfp_mask(mapping) | __GFP_ZERO);
 	folio = __filemap_get_folio(mapping, index, FGP_WRITEBEGIN,
 					mapping_gfp_mask(mapping));
 	if (IS_ERR(folio))
@@ -2882,6 +2885,9 @@ static int ext4_da_write_begin(struct file *file, struct address_space *mapping,
 	}
 
 retry:
+	if (IS_ENABLED(CONFIG_FS_ENCRYPTION))
+		mapping_set_gfp_mask(mapping,
+				     mapping_gfp_mask(mapping) | __GFP_ZERO);
 	folio = __filemap_get_folio(mapping, index, FGP_WRITEBEGIN,
 			mapping_gfp_mask(mapping));
 	if (IS_ERR(folio))
-- 
2.34.1