[PATCH] f2fs: fix use-after-free issue with sbi->stat_info

[Sahitya Tummala]

iput() on sbi->node_inode can update sbi->stat_info
in the below context, if the f2fs_write_checkpoint()
has failed with error.

f2fs_balance_fs_bg+0x1ac/0x1ec
f2fs_write_node_pages+0x4c/0x260
do_writepages+0x80/0xbc
__writeback_single_inode+0xdc/0x4ac
writeback_single_inode+0x9c/0x144
write_inode_now+0xc4/0xec
iput+0x194/0x22c
f2fs_put_super+0x11c/0x1e8
generic_shutdown_super+0x70/0xf4
kill_block_super+0x2c/0x5c
kill_f2fs_super+0x44/0x50
deactivate_locked_super+0x60/0x8c
deactivate_super+0x68/0x74
cleanup_mnt+0x40/0x78

Fix this by moving f2fs_destroy_stats() further below iput().

Signed-off-by: Sahitya Tummala <stummala@xxxxxxxxxxxxxx>
---
 fs/f2fs/super.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
index e184ad4e..df41a3a 100644
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -1058,9 +1058,6 @@ static void f2fs_put_super(struct super_block *sb)
 		f2fs_write_checkpoint(sbi, &cpc);
 	}
 
-	/* f2fs_write_checkpoint can update stat informaion */
-	f2fs_destroy_stats(sbi);
-
 	/*
 	 * normally superblock is clean, so we need to release this.
 	 * In addition, EIO will skip do checkpoint, we need this as well.
@@ -1080,6 +1077,12 @@ static void f2fs_put_super(struct super_block *sb)
 	iput(sbi->node_inode);
 	iput(sbi->meta_inode);
 
+	/*
+	 * iput() can update stat information, if f2fs_write_checkpoint()
+	 * above failed with error.
+	 */
+	f2fs_destroy_stats(sbi);
+
 	/* destroy f2fs internal modules */
 	f2fs_destroy_node_manager(sbi);
 	f2fs_destroy_segment_manager(sbi);
-- 
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