erofs: reject inodes with negative i_size

Negative i_size is never supported, although crafted images with inodes
having negative i_size will NOT lead to security issues in our current
codebase:

The following image can verify this (gzip+base64 encoded):

H4sICCmk4mYAA3Rlc3QuaW1nAGNgGAWjYBSMVPDo4dcH3jP2aTED2TwMKgxMUHHNJY/SQDQX
LxcDIw3tZwXit44MDNpQ/n8gQJZ/vxjijosPuSyZ0DUDgQqcZoKzVYFsDShbHeh6PT29ktTi
Eqz2g/y2pBFiLxDMh4lhs5+W4TAKRsEoGAWjYBSMglEwCkYBPQAAS2DbowAQAAA=

Mark as bad inodes for such corrupted inodes explicitly.

Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/20240912083538.3011860-1-hsiangkao@linux.alibaba.com

diff --git a/fs/erofs/inode.c b/fs/erofs/inode.c
index 7a98df664814add197fd478c59856570a29e815e..db29190656eb2ba0a4907f6ac8264aa380bcb4dd 100644 (file)
--- a/fs/erofs/inode.c
+++ b/fs/erofs/inode.c
@@ -5,7 +5,6 @@
  * Copyright (C) 2021, Alibaba Cloud
  */
 #include "xattr.h"
-
 #include <trace/events/erofs.h>
 
 static int erofs_fill_symlink(struct inode *inode, void *kaddr,
@@ -16,7 +15,7 @@ static int erofs_fill_symlink(struct inode *inode, void *kaddr,
 
        m_pofs += vi->xattr_isize;
        /* check if it cannot be handled with fast symlink scheme */
-       if (vi->datalayout != EROFS_INODE_FLAT_INLINE || inode->i_size < 0 ||
+       if (vi->datalayout != EROFS_INODE_FLAT_INLINE ||
            check_add_overflow(m_pofs, inode->i_size, &off) ||
            off > i_blocksize(inode))
                return 0;
@@ -131,6 +130,11 @@ static int erofs_read_inode(struct inode *inode)
                goto err_out;
        }
 
+       if (unlikely(inode->i_size < 0)) {
+               erofs_err(sb, "negative i_size @ nid %llu", vi->nid);
+               err = -EFSCORRUPTED;
+               goto err_out;
+       }
        switch (inode->i_mode & S_IFMT) {
        case S_IFREG:
        case S_IFDIR:
@@ -186,7 +190,6 @@ static int erofs_read_inode(struct inode *inode)
                inode->i_blocks = round_up(inode->i_size, sb->s_blocksize) >> 9;
        else
                inode->i_blocks = nblks << (sb->s_blocksize_bits - 9);
-
 err_out:
        DBG_BUGON(err);
        erofs_put_metabuf(&buf);