[PATCH 5.14 100/432] f2fs: reduce the scope of setting fsck tag when de->name_len is zero

Greg Kroah-Hartman
2021-09-16T17:23:47Z

From: Yangtao Li <frank.li@vivo.com>

[ Upstream commit d4bf15a7ce172d186d400d606adf4f34a59130d6 ]

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
- f2fs_readdir
- f2fs_read_inline_dir
- ctx->pos = d.max
- f2fs_add_dentry
- f2fs_add_inline_entry
- do_convert_inline_dir
- f2fs_add_regular_entry
- f2fs_readdir
- f2fs_fill_dentries
- 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.

And Chao pointed out that w/o inline conversion, the race condition still
can happen as below:

dir_entry1: A
dir_entry2: B
dir_entry3: C
free slot: _
ctx->pos: ^

Thread A is traversing directory,
ctx-pos moves to below position after readdir() by thread A:
AAAABBBB___
^

Then thread B delete dir_entry2, and create dir_entry3.

Thread A calls readdir() to lookup dirents starting from middle
of new dirent slots as below:
AAAACCCCCC_
^
In these scenarios, the file system is not damaged, and it's hard to
avoid it. But we can bypass tagging FSCK flag if:
a) bit_pos (:= ctx->pos % d->max) is non-zero and
b) before bit_pos moves to first valid dir_entry.

Fixes: ddf06b753a85 ("f2fs: fix to trigger fsck if dirent.name_len is zero")
Signed-off-by: Yangtao Li <frank.li@vivo.com>
[Chao: clean up description]
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/f2fs/dir.c | 14 +++++++++-----
1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/fs/f2fs/dir.c b/fs/f2fs/dir.c
index 456651682daf..c250bf46ef5e 100644
--- a/fs/f2fs/dir.c
+++ b/fs/f2fs/dir.c
@@ -1000,6 +1000,7 @@ int f2fs_fill_dentries(struct dir_context *ctx, struct f2fs_dentry_ptr *d,
struct f2fs_sb_info *sbi = F2FS_I_SB(d->inode);
struct blk_plug plug;
bool readdir_ra = sbi->readdir_ra == 1;
+ bool found_valid_dirent = false;
int err = 0;

bit_pos = ((unsigned long)ctx->pos % d->max);
@@ -1014,13 +1015,15 @@ int f2fs_fill_dentries(struct dir_context *ctx, struct f2fs_dentry_ptr *d,

de = &d->dentry[bit_pos];
if (de->name_len == 0) {
+ if (found_valid_dirent || !bit_pos) {
+ printk_ratelimited(
+ "%sF2FS-fs (%s): invalid namelen(0), ino:%u, run fsck to fix.",
+ KERN_WARNING, sbi->sb->s_id,
+ le32_to_cpu(de->ino));
+ set_sbi_flag(sbi, SBI_NEED_FSCK);
+ }
bit_pos++;
ctx->pos = start_pos + bit_pos;
- printk_ratelimited(
- "%sF2FS-fs (%s): invalid namelen(0), ino:%u, run fsck to fix.",
- KERN_WARNING, sbi->sb->s_id,
- le32_to_cpu(de->ino));
- set_sbi_flag(sbi, SBI_NEED_FSCK);
continue;
}

@@ -1063,6 +1066,7 @@ int f2fs_fill_dentries(struct dir_context *ctx, struct f2fs_dentry_ptr *d,
f2fs_ra_node_page(sbi, le32_to_cpu(de->ino));

ctx->pos = start_pos + bit_pos;
+ found_valid_dirent = true;
}
out:
if (readdir_ra)
--
2.30.2