[PATCH v3 3/3] 9p: skip over-long directory entry names for legacy 9p2000 too

The legacy 9p2000 and 9p2000.u readdir path, v9fs_dir_readdir(), parses
each entry with p9stat_read() and, unlike the 9p2000.L path, never had
a 256-byte name limit: a name of any length up to the wire maximum was
handed to dir_emit(). getdents64() therefore returned names longer than
NAME_MAX that no later syscall can use, and failed with -EIO for names
of PATH_MAX bytes or more.

Apply the same NAME_MAX check as the previous patch does for
v9fs_dir_readdir_dotl(), so both protocol variants behave the same.

Note that this is a behaviour change for 9p2000 and 9p2000.u: entries
with names longer than NAME_MAX used to be listed and are now skipped.

Suggested-by: Christian Schoenebeck <[email protected]>
Link: https://lore.kernel.org/all/3910569.MHq7AAxBmi@weasel/
Signed-off-by: Haobin Wu <[email protected]>
---
 fs/9p/vfs_dir.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/fs/9p/vfs_dir.c b/fs/9p/vfs_dir.c
index 08d1a3429654..31de9ac913f0 100644
--- a/fs/9p/vfs_dir.c
+++ b/fs/9p/vfs_dir.c
@@ -119,6 +119,8 @@ static int v9fs_dir_readdir(struct file *file, struct dir_context *ctx)
 			rdir->tail = n;
 		}
 		while (rdir->head < rdir->tail) {
+			size_t namelen;
+
 			err = p9stat_read(fid->clnt, rdir->buf + rdir->head,
 					  rdir->tail - rdir->head, &st);
 			if (err <= 0) {
@@ -126,8 +128,16 @@ static int v9fs_dir_readdir(struct file *file, struct dir_context *ctx)
 				return -EIO;
 			}
 
-			over = !dir_emit(ctx, st.name, strlen(st.name),
-					QID2INO(&st.qid), dt_type(&st));
+			namelen = strlen(st.name);
+			if (namelen > NAME_MAX) {
+				p9_debug(P9_DEBUG_ERROR,
+					 "skip dentry: name length %zu > NAME_MAX\n",
+					 namelen);
+				over = false;
+			} else {
+				over = !dir_emit(ctx, st.name, namelen,
+						 QID2INO(&st.qid), dt_type(&st));
+			}
 			p9stat_free(&st);
 			if (over)
 				return 0;
-- 
2.54.0 (Apple Git-157)