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

From: Greg Kroah-Hartman
Date: Thu Aug 23 2018 - 04:04:12 EST

4.4-stable review patch. If anyone has any objections, please let me know.


From: Jann Horn <jannh@xxxxxxxxxx>

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

Link: http://lkml.kernel.org/r/20180802151539.5373-1-jannh@xxxxxxxxxx
Fixes: 48b32a3553a5 ("reiserfs: use generic xattr handlers")
Signed-off-by: Jann Horn <jannh@xxxxxxxxxx>
Acked-by: Jeff Mahoney <jeffm@xxxxxxxx>
Cc: Eric Biggers <ebiggers@xxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

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,
- 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);