f2fs: fix to cover read extent cache access with lock

syzbot reports a f2fs bug as below:

BUG: KASAN: slab-use-after-free in sanity_check_extent_cache+0x370/0x410 fs/f2fs/extent_cache.c:46
Read of size 4 at addr ffff8880739ab220 by task syz-executor200/5097

CPU: 0 PID: 5097 Comm: syz-executor200 Not tainted 6.9.0-rc6-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/27/2024
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x241/0x360 lib/dump_stack.c:114
 print_address_description mm/kasan/report.c:377 [inline]
 print_report+0x169/0x550 mm/kasan/report.c:488
 kasan_report+0x143/0x180 mm/kasan/report.c:601
 sanity_check_extent_cache+0x370/0x410 fs/f2fs/extent_cache.c:46
 do_read_inode fs/f2fs/inode.c:509 [inline]
 f2fs_iget+0x33e1/0x46e0 fs/f2fs/inode.c:560
 f2fs_nfs_get_inode+0x74/0x100 fs/f2fs/super.c:3237
 generic_fh_to_dentry+0x9f/0xf0 fs/libfs.c:1413
 exportfs_decode_fh_raw+0x152/0x5f0 fs/exportfs/expfs.c:444
 exportfs_decode_fh+0x3c/0x80 fs/exportfs/expfs.c:584
 do_handle_to_path fs/fhandle.c:155 [inline]
 handle_to_path fs/fhandle.c:210 [inline]
 do_handle_open+0x495/0x650 fs/fhandle.c:226
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xf5/0x240 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

We missed to cover sanity_check_extent_cache() w/ extent cache lock,
so, below race case may happen, result in use after free issue.

- f2fs_iget
 - do_read_inode
  - f2fs_init_read_extent_tree
  : add largest extent entry in to cache
					- shrink
					 - f2fs_shrink_read_extent_tree
					  - __shrink_extent_tree
					   - __detach_extent_node
					   : drop largest extent entry
  - sanity_check_extent_cache
  : access et->largest w/o lock

let's refactor sanity_check_extent_cache() to avoid extent cache access
and call it before f2fs_init_read_extent_tree() to fix this issue.

Reported-by: syzbot+74ebe2104433e9dc610d@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/linux-f2fs-devel/00000000000009beea061740a531@google.comSigned-off-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/extent_cache.c

@@ -19,33 +19,23 @@
 #include "node.h"
 #include <trace/events/f2fs.h>
 
-bool sanity_check_extent_cache(struct inode *inode)
+bool sanity_check_extent_cache(struct inode *inode, struct page *ipage)
 {
 	struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
-	struct f2fs_inode_info *fi = F2FS_I(inode);
-	struct extent_tree *et = fi->extent_tree[EX_READ];
-	struct extent_info *ei;
-
-	if (!et)
-		return true;
+	struct f2fs_extent *i_ext = &F2FS_INODE(ipage)->i_ext;
+	struct extent_info ei;
 
-	ei = &et->largest;
-	if (!ei->len)
-		return true;
+	get_read_extent_info(&ei, i_ext);
 
-	/* Let's drop, if checkpoint got corrupted. */
-	if (is_set_ckpt_flags(sbi, CP_ERROR_FLAG)) {
-		ei->len = 0;
-		et->largest_updated = true;
+	if (!ei.len)
 		return true;
-	}
 
-	if (!f2fs_is_valid_blkaddr(sbi, ei->blk, DATA_GENERIC_ENHANCE) ||
-	    !f2fs_is_valid_blkaddr(sbi, ei->blk + ei->len - 1,
+	if (!f2fs_is_valid_blkaddr(sbi, ei.blk, DATA_GENERIC_ENHANCE) ||
+	    !f2fs_is_valid_blkaddr(sbi, ei.blk + ei.len - 1,
 					DATA_GENERIC_ENHANCE)) {
 		f2fs_warn(sbi, "%s: inode (ino=%lx) extent info [%u, %u, %u] is incorrect, run fsck to fix",
 			  __func__, inode->i_ino,
-			  ei->blk, ei->fofs, ei->len);
+			  ei.blk, ei.fofs, ei.len);
 		return false;
 	}
 	return true;
@@ -394,24 +384,22 @@ void f2fs_init_read_extent_tree(struct inode *inode, struct page *ipage)
 
 	if (!__may_extent_tree(inode, EX_READ)) {
 		/* drop largest read extent */
-		if (i_ext && i_ext->len) {
+		if (i_ext->len) {
 			f2fs_wait_on_page_writeback(ipage, NODE, true, true);
 			i_ext->len = 0;
 			set_page_dirty(ipage);
 		}
-		goto out;
+		set_inode_flag(inode, FI_NO_EXTENT);
+		return;
 	}
 
 	et = __grab_extent_tree(inode, EX_READ);
 
-	if (!i_ext || !i_ext->len)
-		goto out;
-
 	get_read_extent_info(&ei, i_ext);
 
 	write_lock(&et->lock);
-	if (atomic_read(&et->node_cnt))
-		goto unlock_out;
+	if (atomic_read(&et->node_cnt) || !ei.len)
+		goto skip;
 
 	en = __attach_extent_node(sbi, et, &ei, NULL,
 				&et->root.rb_root.rb_node, true);
@@ -423,11 +411,13 @@ void f2fs_init_read_extent_tree(struct inode *inode, struct page *ipage)
 		list_add_tail(&en->list, &eti->extent_list);
 		spin_unlock(&eti->extent_lock);
 	}
-unlock_out:
+skip:
+	/* Let's drop, if checkpoint got corrupted. */
+	if (f2fs_cp_error(sbi)) {
+		et->largest.len = 0;
+		et->largest_updated = true;
+	}
 	write_unlock(&et->lock);
-out:
-	if (!F2FS_I(inode)->extent_tree[EX_READ])
-		set_inode_flag(inode, FI_NO_EXTENT);
 }
 
 void f2fs_init_age_extent_tree(struct inode *inode)

fs/f2fs/f2fs.h

@@ -4190,7 +4190,7 @@ void f2fs_leave_shrinker(struct f2fs_sb_info *sbi);
 /*
  * extent_cache.c
  */
-bool sanity_check_extent_cache(struct inode *inode);
+bool sanity_check_extent_cache(struct inode *inode, struct page *ipage);
 void f2fs_init_extent_tree(struct inode *inode);
 void f2fs_drop_extent_tree(struct inode *inode);
 void f2fs_destroy_extent_node(struct inode *inode);

fs/f2fs/inode.c

@@ -511,16 +511,16 @@ static int do_read_inode(struct inode *inode)
 
 	init_idisk_time(inode);
 
-	/* Need all the flag bits */
-	f2fs_init_read_extent_tree(inode, node_page);
-	f2fs_init_age_extent_tree(inode);
-
-	if (!sanity_check_extent_cache(inode)) {
+	if (!sanity_check_extent_cache(inode, node_page)) {
 		f2fs_put_page(node_page, 1);
 		f2fs_handle_error(sbi, ERROR_CORRUPTED_INODE);
 		return -EFSCORRUPTED;
 	}
 
+	/* Need all the flag bits */
+	f2fs_init_read_extent_tree(inode, node_page);
+	f2fs_init_age_extent_tree(inode);
+
 	f2fs_put_page(node_page, 1);
 
 	stat_inc_inline_xattr(inode);