Re: [f2fs-dev] [PATCH] f2fs: fix ctx->pos in f2fs_read_inline_dir()

From: Chao Yu
Date: Sat Jul 17 2021 - 04:56:24 EST

On 2021/7/17 11:49, Yangtao Li wrote:
I recently found a case where de->name_len is 0 in f2fs_fill_dentries() easily reproduced,
and finally set the fsck flag.

Thread A Thread B

ctx->pos = d.max
set_sbi_flag(sbi, SBI_NEED_FSCK)

Process A opens the folder, and has been reading without closing it. During this period,
Process B created a file under the folder (occupying multiple f2fs_dir_entry, exceeding
the d.max of the inline dir). After creation, process A uses the d.max of inline dir to
read it again, and it will read that de->name_len is 0.

Nice catch!

And returning early in f2fs_read_inline_dir will cause the process to be unable to see
the changes before reopening the file.

So don't return early and remove the modification of ctx->pos in f2fs_read_inline_dir().

Signed-off-by: Yangtao Li <>
fs/f2fs/inline.c | 5 -----
1 file changed, 5 deletions(-)

diff --git a/fs/f2fs/inline.c b/fs/f2fs/inline.c
index 56a20d5c15da..fc6551139a3d 100644
--- a/fs/f2fs/inline.c
+++ b/fs/f2fs/inline.c
@@ -729,9 +729,6 @@ int f2fs_read_inline_dir(struct file *file, struct dir_context *ctx,
make_dentry_ptr_inline(inode, &d, inline_dentry);
- if (ctx->pos == d.max)
- return 0;
ipage = f2fs_get_node_page(F2FS_I_SB(inode), inode->i_ino);
if (IS_ERR(ipage))
return PTR_ERR(ipage);
@@ -747,8 +744,6 @@ int f2fs_read_inline_dir(struct file *file, struct dir_context *ctx,
make_dentry_ptr_inline(inode, &d, inline_dentry);
err = f2fs_fill_dentries(ctx, &d, 0, fstr);

After this function, ctx->pos will point to start position of first free slot after
last dir_entry, we can't guarantee that the free slot won't be used in above race
condition, right?

Moreover, w/o inline conversion, the race condition still can happen as below, right?

dir_entry1: A
dir_entry2: B
dir_entry3: C
free slot: _

Thread B delete dir_entry2, and create dir_entry3.


- if (!err)
- ctx->pos = d.max;
f2fs_put_page(ipage, 0);
return err < 0 ? err : 0;