Re: [syzbot] [v9fs?] WARNING in v9fs_begin_writeback

[Edward Adam Davis <eadavis@qq.com>]

debug

#syz test: upstream c0ecd6388360

diff --git a/fs/9p/fid.c b/fs/9p/fid.c
index de009a33e0e2..b5ccab74bb6f 100644
--- a/fs/9p/fid.c
+++ b/fs/9p/fid.c
@@ -13,6 +13,7 @@
 #include <linux/sched.h>
 #include <net/9p/9p.h>
 #include <net/9p/client.h>
+#include <linux/file.h>
 
 #include "v9fs.h"
 #include "v9fs_vfs.h"
diff --git a/fs/9p/vfs_addr.c b/fs/9p/vfs_addr.c
index a97ceb105cd8..7768cc70439d 100644
--- a/fs/9p/vfs_addr.c
+++ b/fs/9p/vfs_addr.c
@@ -34,6 +34,7 @@ static void v9fs_begin_writeback(struct netfs_io_request *wreq)
 {
 	struct p9_fid *fid;
 
+	printk("ino: %lx, %s\n", wreq->inode->i_ino, __func__);
 	fid = v9fs_fid_find_inode(wreq->inode, true, INVALID_UID, true);
 	if (!fid) {
 		WARN_ONCE(1, "folio expected an open fid inode->i_ino=%lx\n",
diff --git a/fs/9p/vfs_file.c b/fs/9p/vfs_file.c
index 348cc90bf9c5..002c3f7f0ba3 100644
--- a/fs/9p/vfs_file.c
+++ b/fs/9p/vfs_file.c
@@ -22,6 +22,7 @@
 #include <linux/slab.h>
 #include <net/9p/9p.h>
 #include <net/9p/client.h>
+#include <linux/security.h>
 
 #include "v9fs.h"
 #include "v9fs_vfs.h"
@@ -44,6 +45,12 @@ int v9fs_file_open(struct inode *inode, struct file *file)
 	struct p9_fid *fid;
 	int omode;
 
+	if ((file->f_flags & O_RDWR || file->f_flags & O_WRONLY) &&
+	    security_file_permission(file, MAY_WRITE)) {
+		pr_info("file: %p no permission, ino: %lx, %s\n", file, inode->i_ino, __func__);
+		return -EPERM;
+	}
+
 	p9_debug(P9_DEBUG_VFS, "inode: %p file: %p\n", inode, file);
 	v9ses = v9fs_inode2v9ses(inode);
 	if (v9fs_proto_dotl(v9ses))
@@ -397,6 +404,12 @@ v9fs_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
 {
 	struct file *file = iocb->ki_filp;
 	struct p9_fid *fid = file->private_data;
+	struct inode *inode = file_inode(file);
+
+	if (security_file_permission(file, MAY_WRITE)) {
+		pr_info("file: %p no permission, ino: %lx, %s\n", file, inode->i_ino,  __func__);
+		return -EPERM;
+	}
 
 	p9_debug(P9_DEBUG_VFS, "fid %d\n", fid->fid);
 
@@ -460,6 +473,11 @@ v9fs_file_mmap(struct file *filp, struct vm_area_struct *vma)
 	struct inode *inode = file_inode(filp);
 	struct v9fs_session_info *v9ses = v9fs_inode2v9ses(inode);
 
+	if (security_file_permission(filp, MAY_WRITE)) {
+		pr_info("file: %p no permission, ino: %lx, %s\n", filp, inode->i_ino, __func__);
+		return -EPERM;
+	}
+
 	p9_debug(P9_DEBUG_MMAP, "filp :%p\n", filp);
 
 	if (!(v9ses->cache & CACHE_WRITEBACK)) {
diff --git a/fs/netfs/write_issue.c b/fs/netfs/write_issue.c
index 9258d30cffe3..bab69d871381 100644
--- a/fs/netfs/write_issue.c
+++ b/fs/netfs/write_issue.c
@@ -528,6 +528,7 @@ int netfs_writepages(struct address_space *mapping,
 		/* It appears we don't have to handle cyclic writeback wrapping. */
 		WARN_ON_ONCE(wreq && folio_pos(folio) < wreq->start + wreq->submitted);
 
+		printk("ino: %lx, folio: %p, %s\n", wreq->inode->i_ino, folio, __func__);
 		if (netfs_folio_group(folio) != NETFS_FOLIO_COPY_TO_CACHE &&
 		    unlikely(!test_bit(NETFS_RREQ_UPLOAD_TO_SERVER, &wreq->flags))) {
 			set_bit(NETFS_RREQ_UPLOAD_TO_SERVER, &wreq->flags);