[PATCH] 9p: readdir: do not trust pdu content for stat item size

[Dominique Martinet <asmadeus@codewreck.org>]

From: Gertjan Halkes <gertjan@google.com>

v9fs_dir_readdir() could deadloop if a struct was sent with a size set
to -2

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=88021
Signed-off-by: Gertjan Halkes <gertjan@google.com>
Signed-off-by: Dominique Martinet <dominique.martinet@cea.fr>
---

This patch has been sitting in bugzilla for three years, I'll take it
for the next merge window after some testing.
Thanks Gertjan!

 fs/9p/vfs_dir.c   | 8 +++-----
 net/9p/protocol.c | 3 ++-
 2 files changed, 5 insertions(+), 6 deletions(-)

diff --git a/fs/9p/vfs_dir.c b/fs/9p/vfs_dir.c
index 48db9a9f13f9..cb6c4031af55 100644
--- a/fs/9p/vfs_dir.c
+++ b/fs/9p/vfs_dir.c
@@ -105,7 +105,6 @@ static int v9fs_dir_readdir(struct file *file, struct dir_context *ctx)
 	int err = 0;
 	struct p9_fid *fid;
 	int buflen;
-	int reclen = 0;
 	struct p9_rdir *rdir;
 	struct kvec kvec;
 
@@ -138,11 +137,10 @@ static int v9fs_dir_readdir(struct file *file, struct dir_context *ctx)
 		while (rdir->head < rdir->tail) {
 			err = p9stat_read(fid->clnt, rdir->buf + rdir->head,
 					  rdir->tail - rdir->head, &st);
-			if (err) {
+			if (err <= 0) {
 				p9_debug(P9_DEBUG_VFS, "returned %d\n", err);
 				return -EIO;
 			}
-			reclen = st.size+2;
 
 			over = !dir_emit(ctx, st.name, strlen(st.name),
 					 v9fs_qid2ino(&st.qid), dt_type(&st));
@@ -150,8 +148,8 @@ static int v9fs_dir_readdir(struct file *file, struct dir_context *ctx)
 			if (over)
 				return 0;
 
-			rdir->head += reclen;
-			ctx->pos += reclen;
+			rdir->head += err;
+			ctx->pos += err;
 		}
 	}
 }
diff --git a/net/9p/protocol.c b/net/9p/protocol.c
index ee32bbf12675..b4d80c533f89 100644
--- a/net/9p/protocol.c
+++ b/net/9p/protocol.c
@@ -571,9 +571,10 @@ int p9stat_read(struct p9_client *clnt, char *buf, int len, struct p9_wstat *st)
 	if (ret) {
 		p9_debug(P9_DEBUG_9P, "<<< p9stat_read failed: %d\n", ret);
 		trace_9p_protocol_dump(clnt, &fake_pdu);
+		return ret;
 	}
 
-	return ret;
+	return fake_pdu.offset;
 }
 EXPORT_SYMBOL(p9stat_read);
 
-- 
2.17.1