linux-kernel - [PATCH AUTOSEL 4.19 12/12] readdir: make sure to verify directory entry for legacy interfaces too

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Message-Id: <20210419204517.6770-12-sashal@kernel.org>
Date:   Mon, 19 Apr 2021 16:45:17 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Sasha Levin <sashal@...nel.org>, linux-fsdevel@...r.kernel.org
Subject: [PATCH AUTOSEL 4.19 12/12] readdir: make sure to verify directory entry for legacy interfaces too

From: Linus Torvalds <torvalds@...ux-foundation.org>

[ Upstream commit 0c93ac69407d63a85be0129aa55ffaec27ffebd3 ]

This does the directory entry name verification for the legacy
"fillonedir" (and compat) interface that goes all the way back to the
dark ages before we had a proper dirent, and the readdir() system call
returned just a single entry at a time.

Nobody should use this interface unless you still have binaries from
1991, but let's do it right.

This came up during discussions about unsafe_copy_to_user() and proper
checking of all the inputs to it, as the networking layer is looking to
use it in a few new places.  So let's make sure the _old_ users do it
all right and proper, before we add new ones.

See also commit 8a23eb804ca4 ("Make filldir[64]() verify the directory
entry filename is valid") which did the proper modern interfaces that
people actually use. It had a note:

    Note that I didn't bother adding the checks to any legacy interfaces
    that nobody uses.

which this now corrects.  Note that we really don't care about POSIX and
the presense of '/' in a directory entry, but verify_dirent_name() also
ends up doing the proper name length verification which is what the
input checking discussion was about.

[ Another option would be to remove the support for this particular very
  old interface: any binaries that use it are likely a.out binaries, and
  they will no longer run anyway since we removed a.out binftm support
  in commit eac616557050 ("x86: Deprecate a.out support").

  But I'm not sure which came first: getdents() or ELF support, so let's
  pretend somebody might still have a working binary that uses the
  legacy readdir() case.. ]

Link: https://lore.kernel.org/lkml/CAHk-=wjbvzCAhAtvG0d81W5o0-KT5PPTHhfJ5ieDFq+bGtgOYg@mail.gmail.com/
Acked-by: Al Viro <viro@...iv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 fs/readdir.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/fs/readdir.c b/fs/readdir.c
index 443270f635f4..3c5ce8a0ddc9 100644
--- a/fs/readdir.c
+++ b/fs/readdir.c
@@ -132,6 +132,9 @@ static int fillonedir(struct dir_context *ctx, const char *name, int namlen,

 	if (buf->result)
 		return -EINVAL;
+	buf->result = verify_dirent_name(name, namlen);
+	if (buf->result < 0)
+		return buf->result;
 	d_ino = ino;
 	if (sizeof(d_ino) < sizeof(ino) && d_ino != ino) {
 		buf->result = -EOVERFLOW;
@@ -398,6 +401,9 @@ static int compat_fillonedir(struct dir_context *ctx, const char *name,

 	if (buf->result)
 		return -EINVAL;
+	buf->result = verify_dirent_name(name, namlen);
+	if (buf->result < 0)
+		return buf->result;
 	d_ino = ino;
 	if (sizeof(d_ino) < sizeof(ino) && d_ino != ino) {
 		buf->result = -EOVERFLOW;
-- 
2.30.2