erofs: fix the out-of-bounds nameoff handling for trailing dirents

Currently we already have boundary-checks for nameoffs, but the trailing
dirents are special since the namelens are calculated with strnlen()
with unchecked nameoffs.

If a crafted EROFS has a trailing dirent with nameoff >= maxsize,
maxsize - nameoff can underflow, causing strnlen() to read past the
directory block.

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>
Reviewed-by: Chao Yu <chao@kernel.org>

diff --git a/fs/erofs/dir.c b/fs/erofs/dir.c
index e5132575b9d3ef958a8acbe80bd0d2ddbd865135..4aa52a5f204a0f23b93227b2a042acbdafb54390 100644 (file)
--- 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;