From 7e55d65c56a03dcd2c5d7c49d37c5a74b55d4bd6 Mon Sep 17 00:00:00 2001 From: Li Qiang Date: Tue, 1 Nov 2016 12:00:40 +0100 Subject: [PATCH] 9pfs: fix integer overflow issue in xattr read/write MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit The v9fs_xattr_read() and v9fs_xattr_write() are passed a guest originated offset: they must ensure this offset does not go beyond the size of the extended attribute that was set in v9fs_xattrcreate(). Unfortunately, the current code implement these checks with unsafe calculations on 32 and 64 bit values, which may allow a malicious guest to cause OOB access anyway. Fix this by comparing the offset and the xattr size, which are both uint64_t, before trying to compute the effective number of bytes to read or write. Suggested-by: Greg Kurz Signed-off-by: Li Qiang Reviewed-by: Greg Kurz Reviewed-By: Guido Günther Signed-off-by: Greg Kurz --- hw/9pfs/9p.c | 32 ++++++++++++-------------------- 1 file changed, 12 insertions(+), 20 deletions(-) diff --git a/hw/9pfs/9p.c b/hw/9pfs/9p.c index ab18ef2..7705ead 100644 --- a/hw/9pfs/9p.c +++ b/hw/9pfs/9p.c @@ -1637,20 +1637,17 @@ static int v9fs_xattr_read(V9fsState *s, V9fsPDU *pdu, V9fsFidState *fidp, { ssize_t err; size_t offset = 7; - int read_count; - int64_t xattr_len; + uint64_t read_count; V9fsVirtioState *v = container_of(s, V9fsVirtioState, state); VirtQueueElement *elem = v->elems[pdu->idx]; - xattr_len = fidp->fs.xattr.len; - read_count = xattr_len - off; + if (fidp->fs.xattr.len < off) { + read_count = 0; + } else { + read_count = fidp->fs.xattr.len - off; + } if (read_count > max_count) { read_count = max_count; - } else if (read_count < 0) { - /* - * read beyond XATTR value - */ - read_count = 0; } err = pdu_marshal(pdu, offset, "d", read_count); if (err < 0) { @@ -1979,23 +1976,18 @@ static int v9fs_xattr_write(V9fsState *s, V9fsPDU *pdu, V9fsFidState *fidp, { int i, to_copy; ssize_t err = 0; - int write_count; - int64_t xattr_len; + uint64_t write_count; size_t offset = 7; - xattr_len = fidp->fs.xattr.len; - write_count = xattr_len - off; - if (write_count > count) { - write_count = count; - } else if (write_count < 0) { - /* - * write beyond XATTR value len specified in - * xattrcreate - */ + if (fidp->fs.xattr.len < off) { err = -ENOSPC; goto out; } + write_count = fidp->fs.xattr.len - off; + if (write_count > count) { + write_count = count; + } err = pdu_marshal(pdu, offset, "d", write_count); if (err < 0) { return err; -- 2.7.3