ext4: clear buffer verified flag if read meta block from disk

The metadata buffer is no longer trusted after we read it from disk
again because it is not uptodate for some reasons (e.g. failed to write
back). Otherwise we may get below memory corruption problem in
ext4_ext_split()->memset() if we read stale data from the newly
allocated extent block on disk which has been failed to async write
out but miss verify again since the verified bit has already been set
on the buffer.

[   29.774674] BUG: unable to handle kernel paging request at ffff88841949d000
...
[   29.783317] Oops: 0002 [#2] SMP
[   29.784219] R10: 00000000000f4240 R11: 0000000000002e28 R12: ffff88842fa1c800
[   29.784627] CPU: 1 PID: 126 Comm: kworker/u4:3 Tainted: G      D W
[   29.785546] R13: ffffffff9cddcc20 R14: ffffffff9cddd420 R15: ffff88842fa1c2f8
[   29.786679] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),BIOS ?-20190727_0738364
[   29.787588] FS:  0000000000000000(0000) GS:ffff88842fa00000(0000) knlGS:0000000000000000
[   29.789288] Workqueue: writeback wb_workfn
[   29.790319] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   29.790321]  (flush-8:0)
[   29.790844] CR2: 0000000000000008 CR3: 00000004234f2000 CR4: 00000000000006f0
[   29.791924] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[   29.792839] RIP: 0010:__memset+0x24/0x30
[   29.793739] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[   29.794256] Code: 90 90 90 90 90 90 0f 1f 44 00 00 49 89 f9 48 89 d1 83 e2 07 48 c1 e9 033
[   29.795161] Kernel panic - not syncing: Fatal exception in interrupt
...
[   29.808149] Call Trace:
[   29.808475]  ext4_ext_insert_extent+0x102e/0x1be0
[   29.809085]  ext4_ext_map_blocks+0xa89/0x1bb0
[   29.809652]  ext4_map_blocks+0x290/0x8a0
[   29.809085]  ext4_ext_map_blocks+0xa89/0x1bb0
[   29.809652]  ext4_map_blocks+0x290/0x8a0
[   29.810161]  ext4_writepages+0xc85/0x17c0
...

Fix this by clearing buffer's verified bit if we read meta block from
disk again.

Signed-off-by: zhangyi (F) <yi.zhang@huawei.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20200924073337.861472-2-yi.zhang@huawei.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/balloc.c

@@ -494,6 +494,7 @@ ext4_read_block_bitmap_nowait(struct super_block *sb, ext4_group_t block_group,
 	 * submit the buffer_head for reading
 	 */
 	set_buffer_new(bh);
+	clear_buffer_verified(bh);
 	trace_ext4_read_block_bitmap_load(sb, block_group, ignore_locked);
 	bh->b_end_io = ext4_end_bitmap_read;
 	get_bh(bh);

fs/ext4/extents.c

@@ -501,6 +501,7 @@ __read_extent_tree_block(const char *function, unsigned int line,
 
 	if (!bh_uptodate_or_lock(bh)) {
 		trace_ext4_ext_load_extent(inode, pblk, _RET_IP_);
+		clear_buffer_verified(bh);
 		err = bh_submit_read(bh);
 		if (err < 0)
 			goto errout;

fs/ext4/ialloc.c

@@ -188,6 +188,7 @@ ext4_read_inode_bitmap(struct super_block *sb, ext4_group_t block_group)
 	/*
 	 * submit the buffer_head for reading
 	 */
+	clear_buffer_verified(bh);
 	trace_ext4_load_inode_bitmap(sb, block_group);
 	bh->b_end_io = ext4_end_bitmap_read;
 	get_bh(bh);

fs/ext4/inode.c

@@ -884,6 +884,7 @@ struct buffer_head *ext4_bread(handle_t *handle, struct inode *inode,
 		return bh;
 	if (!bh || ext4_buffer_uptodate(bh))
 		return bh;
+	clear_buffer_verified(bh);
 	ll_rw_block(REQ_OP_READ, REQ_META | REQ_PRIO, 1, &bh);
 	wait_on_buffer(bh);
 	if (buffer_uptodate(bh))
@@ -909,9 +910,11 @@ int ext4_bread_batch(struct inode *inode, ext4_lblk_t block, int bh_count,
 
 	for (i = 0; i < bh_count; i++)
 		/* Note that NULL bhs[i] is valid because of holes. */
-		if (bhs[i] && !ext4_buffer_uptodate(bhs[i]))
+		if (bhs[i] && !ext4_buffer_uptodate(bhs[i])) {
+			clear_buffer_verified(bhs[i]);
 			ll_rw_block(REQ_OP_READ, REQ_META | REQ_PRIO, 1,
 				    &bhs[i]);
+		}
 
 	if (!wait)
 		return 0;

fs/ext4/super.c

@@ -156,6 +156,7 @@ ext4_sb_bread(struct super_block *sb, sector_t block, int op_flags)
 		return ERR_PTR(-ENOMEM);
 	if (ext4_buffer_uptodate(bh))
 		return bh;
+	clear_buffer_verified(bh);
 	ll_rw_block(REQ_OP_READ, REQ_META | op_flags, 1, &bh);
 	wait_on_buffer(bh);
 	if (buffer_uptodate(bh))