[PATCH] f2fs: atomic: fix UAF issue on f2fs_inode_info.atomic_inode

[Chao Yu <chao@kernel.org>]

- ioctl(F2FS_IOC_GARBAGE_COLLECT_RANGE)		- shrink
 - f2fs_gc
  - gc_data_segment
   - ra_data_block(cow_inode)
    - mapping = F2FS_I(inode)->atomic_inode->i_mapping
    : f2fs_is_cow_file(cow_inode) is true
						 - f2fs_evict_inode(atomic_inode)
						  - clear_inode_flag(fi->cow_inode, FI_COW_FILE)
						  - F2FS_I(fi->cow_inode)->atomic_inode = NULL
						  ...
						  - truncate_inode_pages_final(atomic_inode)
    - f2fs_grab_cache_folio(mapping)
    : create folio in atomic_inode->mapping
						  - clear_inode(atomic_inode)
						   - BUG_ON(atomic_inode->i_data.nrpages)

We need to add a reference on fi->atomic_inode before using its mapping
field during garbage collection, otherwise, it will cause UAF issue.

Cc: stable@kernel.org
Cc: Daeho Jeong <daehojeong@google.com>
Cc: Sunmin Jeong <s_min.jeong@samsung.com>
Fixes: 3db1de0e582c ("f2fs: change the current atomic write way")
Fixes: f18d00769336 ("f2fs: use meta inode for GC of COW file")
Signed-off-by: Chao Yu <chao@kernel.org>
---
 fs/f2fs/gc.c    | 50 +++++++++++++++++++++++++++++++++++++++++--------
 fs/f2fs/inode.c | 11 ++++++++---
 2 files changed, 50 insertions(+), 11 deletions(-)

diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
index 3048cc47b5e0..0e537508df20 100644
--- a/fs/f2fs/gc.c
+++ b/fs/f2fs/gc.c
@@ -1220,8 +1220,8 @@ static bool is_alive(struct f2fs_sb_info *sbi, struct f2fs_summary *sum,
 static int ra_data_block(struct inode *inode, pgoff_t index)
 {
 	struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
-	struct address_space *mapping = f2fs_is_cow_file(inode) ?
-				F2FS_I(inode)->atomic_inode->i_mapping : inode->i_mapping;
+	struct address_space *mapping = inode->i_mapping;
+	struct inode *atomic_inode = NULL;
 	struct dnode_of_data dn;
 	struct folio *folio, *efolio;
 	struct f2fs_io_info fio = {
@@ -1236,9 +1236,22 @@ static int ra_data_block(struct inode *inode, pgoff_t index)
 	};
 	int err = 0;
 
+	f2fs_down_read(&F2FS_I(inode)->i_sem);
+	if (f2fs_is_cow_file(inode)) {
+		atomic_inode = igrab(F2FS_I(inode)->atomic_inode);
+		if (!atomic_inode) {
+			f2fs_up_read(&F2FS_I(inode)->i_sem);
+			return -EBUSY;
+		}
+		mapping = atomic_inode->i_mapping;
+	}
+	f2fs_up_read(&F2FS_I(inode)->i_sem);
+
 	folio = f2fs_grab_cache_folio(mapping, index, true);
-	if (IS_ERR(folio))
-		return PTR_ERR(folio);
+	if (IS_ERR(folio)) {
+		err = PTR_ERR(folio);
+		goto out_iput;
+	}
 
 	if (f2fs_lookup_read_extent_cache_block(inode, index,
 						&dn.data_blkaddr)) {
@@ -1299,11 +1312,16 @@ static int ra_data_block(struct inode *inode, pgoff_t index)
 	f2fs_update_iostat(sbi, inode, FS_DATA_READ_IO, F2FS_BLKSIZE);
 	f2fs_update_iostat(sbi, NULL, FS_GDATA_READ_IO, F2FS_BLKSIZE);
 
+	if (atomic_inode)
+		iput(atomic_inode);
 	return 0;
 put_encrypted_page:
 	f2fs_put_page(fio.encrypted_page, true);
 put_folio:
 	f2fs_folio_put(folio, true);
+out_iput:
+	if (atomic_inode)
+		iput(atomic_inode);
 	return err;
 }
 
@@ -1314,8 +1332,8 @@ static int ra_data_block(struct inode *inode, pgoff_t index)
 static int move_data_block(struct inode *inode, block_t bidx,
 				int gc_type, unsigned int segno, int off)
 {
-	struct address_space *mapping = f2fs_is_cow_file(inode) ?
-				F2FS_I(inode)->atomic_inode->i_mapping : inode->i_mapping;
+	struct address_space *mapping = inode->i_mapping;
+	struct inode *atomic_inode = NULL;
 	struct f2fs_io_info fio = {
 		.sbi = F2FS_I_SB(inode),
 		.ino = inode->i_ino,
@@ -1337,10 +1355,23 @@ static int move_data_block(struct inode *inode, block_t bidx,
 				(fio.sbi->gc_mode != GC_URGENT_HIGH) ?
 				CURSEG_ALL_DATA_ATGC : CURSEG_COLD_DATA;
 
+	f2fs_down_read(&F2FS_I(inode)->i_sem);
+	if (f2fs_is_cow_file(inode)) {
+		atomic_inode = igrab(F2FS_I(inode)->atomic_inode);
+		if (!atomic_inode) {
+			f2fs_up_read(&F2FS_I(inode)->i_sem);
+			return -EBUSY;
+		}
+		mapping = atomic_inode->i_mapping;
+	}
+	f2fs_up_read(&F2FS_I(inode)->i_sem);
+
 	/* do not read out */
 	folio = f2fs_grab_cache_folio(mapping, bidx, false);
-	if (IS_ERR(folio))
-		return PTR_ERR(folio);
+	if (IS_ERR(folio)) {
+		err = PTR_ERR(folio);
+		goto out_iput;
+	}
 
 	if (!check_valid_map(F2FS_I_SB(inode), segno, off)) {
 		err = -ENOENT;
@@ -1473,6 +1504,9 @@ static int move_data_block(struct inode *inode, block_t bidx,
 	folio_unlock(folio);
 	folio_end_dropbehind(folio);
 	folio_put(folio);
+out_iput:
+	if (atomic_inode)
+		iput(atomic_inode);
 	return err;
 }
 
diff --git a/fs/f2fs/inode.c b/fs/f2fs/inode.c
index 12f982f87f15..315682e5da53 100644
--- a/fs/f2fs/inode.c
+++ b/fs/f2fs/inode.c
@@ -875,10 +875,15 @@ void f2fs_evict_inode(struct inode *inode)
 	f2fs_abort_atomic_write(inode, true);
 
 	if (fi->cow_inode && f2fs_is_cow_file(fi->cow_inode)) {
-		clear_inode_flag(fi->cow_inode, FI_COW_FILE);
-		F2FS_I(fi->cow_inode)->atomic_inode = NULL;
-		iput(fi->cow_inode);
+		struct inode *cow_inode = fi->cow_inode;
+
+		f2fs_down_write(&F2FS_I(cow_inode)->i_sem);
+		clear_inode_flag(cow_inode, FI_COW_FILE);
+		F2FS_I(cow_inode)->atomic_inode = NULL;
 		fi->cow_inode = NULL;
+		f2fs_up_write(&F2FS_I(cow_inode)->i_sem);
+
+		iput(cow_inode);
 	}
 
 	trace_f2fs_evict_inode(inode);
-- 
2.49.0