linux-kernel - [PATCH] vfs: Fix refcounting of filenames in fs

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Message-ID: <155292822993.1511.7755301484525814050.stgit@warthog.procyon.org.uk>
Date:   Mon, 18 Mar 2019 16:57:09 +0000
From:   David Howells <dhowells@...hat.com>
To:     viro@...iv.linux.org.uk
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        dhowells@...hat.com
Subject: [PATCH] vfs: Fix refcounting of filenames in fs_parser

Fix an overput in which filename_lookup() unconditionally drops a ref to
the filename it was given, but this isn't taken account of in the caller,
fs_lookup_param().

Addresses-Coverity-ID: 1443811 ("Use after free")
Signed-off-by: David Howells <dhowells@...hat.com>
---

 fs/fs_parser.c |    1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/fs_parser.c b/fs/fs_parser.c
index 842e8f749db6..be86703ec371 100644
--- a/fs/fs_parser.c
+++ b/fs/fs_parser.c
@@ -268,6 +268,7 @@ int fs_lookup_param(struct fs_context *fc,
 		return invalf(fc, "%s: not usable as path", param->key);
 	}
 
+	f->refcnt++; /* filename_lookup() drops our ref. */
 	ret = filename_lookup(param->dirfd, f, flags, _path, NULL);
 	if (ret < 0) {
 		errorf(fc, "%s: Lookup failure for '%s'", param->key, f->name);