[PATCH] cifs: fix skipping to incorrect offset in emit_cached_dirents

[Ronnie Sahlberg <lsahlber@redhat.com>]

When application has done lseek() to a different offset on a directory fd
we skipped one entry too many before we start emitting directory entries
from the cache.

Also change cifs_filldir() to return -EEXIST when we encouter a dot-directory in the
reply from the server. Check for this in the caller and skip caching the entry and
skip incprementing ctx->pos or else we end up emitting a sequence of directory entries with
holes in the ctx->pos space.

Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com>
---
 fs/cifs/readdir.c | 25 ++++++++++++++++++-------
 1 file changed, 18 insertions(+), 7 deletions(-)

diff --git a/fs/cifs/readdir.c b/fs/cifs/readdir.c
index 8e060c00c969..0c71a771b256 100644
--- a/fs/cifs/readdir.c
+++ b/fs/cifs/readdir.c
@@ -847,14 +847,14 @@ static bool emit_cached_dirents(struct cached_dirents *cde,
 	int rc;
 
 	list_for_each_entry(dirent, &cde->entries, entry) {
-		if (ctx->pos >= dirent->pos)
+		if (ctx->pos > dirent->pos)
 			continue;
-		ctx->pos = dirent->pos;
 		rc = dir_emit(ctx, dirent->name, dirent->namelen,
 			      dirent->fattr.cf_uniqueid,
 			      dirent->fattr.cf_dtype);
 		if (!rc)
 			return rc;
+		ctx->pos++;
 	}
 	return true;
 }
@@ -965,7 +965,7 @@ static int cifs_filldir(char *find_entry, struct file *file,
 
 	/* skip . and .. since we added them first */
 	if (cifs_entry_is_dot(&de, file_info->srch_inf.unicode))
-		return 0;
+		return -EEXIST;
 
 	if (file_info->srch_inf.unicode) {
 		struct nls_table *nlt = cifs_sb->local_nls;
@@ -1183,6 +1183,17 @@ int cifs_readdir(struct file *file, struct dir_context *ctx)
 		*tmp_buf = 0;
 		rc = cifs_filldir(current_entry, file, ctx,
 				  tmp_buf, max_len, cfid);
+		/*
+		 * If we got a dot directory, just skip to the next entry.
+		 * We have already emitted it.
+		 */
+		if (rc == -EEXIST) {
+			current_entry =
+				nxt_dir_entry(current_entry, end_of_smb,
+					      cifsFile->srch_inf.info_level);
+			rc = 0;
+			continue;
+		}
 		if (rc) {
 			if (rc > 0)
 				rc = 0;
@@ -1202,10 +1213,10 @@ int cifs_readdir(struct file *file, struct dir_context *ctx)
 				 ctx->pos, tmp_buf);
 			cifs_save_resume_key(current_entry, cifsFile);
 			break;
-		} else
-			current_entry =
-				nxt_dir_entry(current_entry, end_of_smb,
-					cifsFile->srch_inf.info_level);
+		}
+		current_entry =
+			nxt_dir_entry(current_entry, end_of_smb,
+				      cifsFile->srch_inf.info_level);
 	}
 	kfree(tmp_buf);
 
-- 
2.35.3