[PATCH 4.4 79/79] reiserfs: fix broken xattr handling (heap corruption, bad retval)

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

4.4-stable 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>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 fs/reiserfs/xattr.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/fs/reiserfs/xattr.c
+++ b/fs/reiserfs/xattr.c
@@ -791,8 +791,10 @@ static int listxattr_filler(struct dir_c
 			size = handler->list(handler, b->dentry,
 					     b->buf + b->pos, b->size, name,
 					     namelen);
-			if (size > b->size)
+			if (b->pos + size > b->size) {
+				b->pos = -ERANGE;
 				return -ERANGE;
+			}
 		} else {
 			size = handler->list(handler, b->dentry,
 					     NULL, 0, name, namelen);