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From:   Ben Hutchings <ben@decadent.org.uk>
To:     linux-kernel@vger.kernel.org, stable@vger.kernel.org
CC:     akpm@linux-foundation.org, "Al Viro" <viro@zeniv.linux.org.uk>,
        "Linus Torvalds" <torvalds@linux-foundation.org>,
        "Jeff Mahoney" <jeffm@suse.com>,
        "Eric Biggers" <ebiggers@google.com>,
        "Jann Horn" <jannh@google.com>
Date:   Sun, 09 Dec 2018 21:50:33 +0000
Message-ID: <lsq.1544392233.687730563@decadent.org.uk>
Subject: [PATCH 3.16 155/328] reiserfs: fix broken xattr handling (heap
 corruption, bad retval)
In-Reply-To: <lsq.1544392232.713909046@decadent.org.uk>
Sender: linux-kernel-owner@vger.kernel.org
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3.16.62-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Jann Horn <jannh@google.com>

commit a13f085d111e90469faf2d9965eb39b11c114d7e upstream.

This fixes the following issues:

- When a buffer size is supplied to reiserfs_listxattr() such that each
  individual name fits, but the concatenation of all names doesn't fit,
  reiserfs_listxattr() overflows the supplied buffer.  This leads to a
  kernel heap overflow (verified using KASAN) followed by an out-of-bounds
  usercopy and is therefore a security bug.

- When a buffer size is supplied to reiserfs_listxattr() such that a
  name doesn't fit, -ERANGE should be returned.  But reiserfs instead just
  truncates the list of names; I have verified that if the only xattr on a
  file has a longer name than the supplied buffer length, listxattr()
  incorrectly returns zero.

With my patch applied, -ERANGE is returned in both cases and the memory
corruption doesn't happen anymore.

Credit for making me clean this code up a bit goes to Al Viro, who pointed
out that the ->actor calling convention is suboptimal and should be
changed.

Link: http://lkml.kernel.org/r/20180802151539.5373-1-jannh@google.com
Fixes: 48b32a3553a5 ("reiserfs: use generic xattr handlers")
Signed-off-by: Jann Horn <jannh@google.com>
Acked-by: Jeff Mahoney <jeffm@suse.com>
Cc: Eric Biggers <ebiggers@google.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
[bwh: Backported to 3.16:
 - The xattr handler's list operation does the copy, so also update the
   buffer size we pass to it
 - Adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
--- a/fs/reiserfs/xattr.c
+++ b/fs/reiserfs/xattr.c
@@ -822,10 +822,12 @@ static int listxattr_filler(void *buf, c
 			return 0;
 		if (b->buf) {
 			size = handler->list(b->dentry, b->buf + b->pos,
-					 b->size, name, namelen,
+					 b->size - b->pos, name, namelen,
 					 handler->flags);
-			if (size > b->size)
+			if (b->pos + size > b->size) {
+				b->pos = -ERANGE;
 				return -ERANGE;
+			}
 		} else {
 			size = handler->list(b->dentry, NULL, 0, name,
 					     namelen, handler->flags);