[PATCH v4] erofs: fix the out-of-bounds nameoff handling for trailing dirents

Gao Xiang
2026-04-21T08:00:00Z

nameoff0 should also be verified to be a multiple of
`sizeof(struct erofs_dirent)` as well [1].

[1] https://sashiko.dev/#/patchset/20260416063511.3173774-1-hsiangkao%40linux.alibaba.com

Fixes: 3aa8ec716e52 ("staging: erofs: add directory operations")
Fixes: 33bac912840f ("staging: erofs: keep corrupted fs from crashing kernel in erofs_readdir()")
Reported-by: Yuhao Jiang <danisjiang@gmail.com>
Reported-by: Junrui Luo <moonafterrain@outlook.com>
Closes: https://lore.kernel.org/r/A0FD7E0F-7558-49B0-8BC8-EB1ECDB2479A@outlook.com
Cc: stable@vger.kernel.org
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
---
v4:
- switch to `if (!nameoff || nameoff >= bsz || (nameoff % sizeof(*de)))`
as suggested by Chao.

fs/erofs/dir.c | 28 +++++++++++++++-------------
1 file changed, 15 insertions(+), 13 deletions(-)

diff --git a/fs/erofs/dir.c b/fs/erofs/dir.c
index e5132575b9d3..4aa52a5f204a 100644
--- a/fs/erofs/dir.c
+++ b/fs/erofs/dir.c
@@ -19,20 +19,18 @@ static int erofs_fill_dentries(struct inode *dir, struct dir_context *ctx,
const char *de_name = (char *)dentry_blk + nameoff;
unsigned int de_namelen;

- /* the last dirent in the block? */
- if (de + 1 >= end)
- de_namelen = strnlen(de_name, maxsize - nameoff);
- else
+ /* non-trailing dirent in the directory block? */
+ if (de + 1 < end)
de_namelen = le16_to_cpu(de[1].nameoff) - nameoff;
+ else if (maxsize <= nameoff)
+ goto err_bogus;
+ else
+ de_namelen = strnlen(de_name, maxsize - nameoff);

- /* a corrupted entry is found */
- if (nameoff + de_namelen > maxsize ||
- de_namelen > EROFS_NAME_LEN) {
- erofs_err(dir->i_sb, "bogus dirent @ nid %llu",
- EROFS_I(dir)->nid);
- DBG_BUGON(1);
- return -EFSCORRUPTED;
- }
+ /* a corrupted entry is found (including negative namelen) */
+ if (!in_range32(de_namelen, 1, EROFS_NAME_LEN) ||
+ nameoff + de_namelen > maxsize)
+ goto err_bogus;

if (!dir_emit(ctx, de_name, de_namelen,
erofs_nid_to_ino64(EROFS_SB(dir->i_sb),
@@ -42,6 +40,10 @@ static int erofs_fill_dentries(struct inode *dir, struct dir_context *ctx,
ctx->pos += sizeof(struct erofs_dirent);
}
return 0;
+err_bogus:
+ erofs_err(dir->i_sb, "bogus dirent @ nid %llu", EROFS_I(dir)->nid);
+ DBG_BUGON(1);
+ return -EFSCORRUPTED;
}

static int erofs_readdir(struct file *f, struct dir_context *ctx)
@@ -88,7 +90,7 @@ static int erofs_readdir(struct file *f, struct dir_context *ctx)
}

nameoff = le16_to_cpu(de->nameoff);
- if (nameoff < sizeof(struct erofs_dirent) || nameoff >= bsz) {
+ if (!nameoff || nameoff >= bsz || (nameoff % sizeof(*de))) {
erofs_err(sb, "invalid de[0].nameoff %u @ nid %llu",
nameoff, EROFS_I(dir)->nid);
err = -EFSCORRUPTED;
--
2.43.5