[PATCH 5.15.y] erofs: fix incorrect symlink detection in fast symlink - Linux-stable-mirror

18 Dec 2024

commit 9ed50b8231e37b1ae863f5dec8153b98d9f389b4 upstream.
Fast symlink can be used if the on-disk symlink data is stored
in the same block as the on-disk inode, so we don’t need to trigger
another I/O for symlink data.  However, currently fs correction could be
reported _incorrectly_ if inode xattrs are too large.
In fact, these should be valid images although they cannot be handled as
fast symlinks.
Many thanks to Colin for reporting this!
Reported-by: Colin Walters walters@verbum.org
Reported-by: https://honggfuzz.dev/
Link: https://lore.kernel.org/r/bb2dd430-7de0-47da-ae5b-82ab2dd4d945@app.fastmail....
Fixes: 431339ba9042 ("staging: erofs: add inode operations")
[ Note that it's a runtime misbehavior instead of a security issue. ]
Link: https://lore.kernel.org/r/20240909031911.1174718-1-hsiangkao@linux.alibaba.c...
Signed-off-by: Gao Xiang hsiangkao@linux.alibaba.com
---
 fs/erofs/inode.c | 20 ++++++--------------
 1 file changed, 6 insertions(+), 14 deletions(-)

diff --git a/fs/erofs/inode.c b/fs/erofs/inode.c
index 638bb70d0d65..c68258ae70d3 100644
--- a/fs/erofs/inode.c
+++ b/fs/erofs/inode.c
@@ -219,11 +219,14 @@ static int erofs_fill_symlink(struct inode *inode, void *data,
    		      unsigned int m_pofs)
 {
    struct erofs_inode *vi = EROFS_I(inode);
+	loff_t off;
    char *lnk;
-	/* if it cannot be handled with fast symlink scheme */
-	if (vi->datalayout != EROFS_INODE_FLAT_INLINE ||
-	    inode->i_size >= PAGE_SIZE || inode->i_size < 0) {
+	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 ||
+	    check_add_overflow(m_pofs, inode->i_size, &off) ||
+	    off > i_blocksize(inode)) {
    	inode->i_op = &erofs_symlink_iops;
    	return 0;
    }
@@ -232,17 +235,6 @@ static int erofs_fill_symlink(struct inode *inode, void *data,
    if (!lnk)
    	return -ENOMEM;
-	m_pofs += vi->xattr_isize;
-	/* inline symlink data shouldn't cross page boundary as well */
-	if (m_pofs + inode->i_size > PAGE_SIZE) {
-		kfree(lnk);
-		erofs_err(inode->i_sb,
-			  "inline data cross block boundary @ nid %llu",
-			  vi->nid);
-		DBG_BUGON(1);
-		return -EFSCORRUPTED;
-	}
-
    memcpy(lnk, data + m_pofs, inode->i_size);
    lnk[inode->i_size] = '\0';
-- 
2.43.5



    