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From: Li Qiang <liqiang6-s@360.cn>
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Date: Tue, 1 Nov 2016 12:00:40 +0100
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Subject: [PATCH] 9pfs: fix integer overflow issue in xattr read/write
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MIME-Version: 1.0
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Content-Type: text/plain; charset=UTF-8
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Content-Transfer-Encoding: 8bit
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The v9fs_xattr_read() and v9fs_xattr_write() are passed a guest
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originated offset: they must ensure this offset does not go beyond
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the size of the extended attribute that was set in v9fs_xattrcreate().
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Unfortunately, the current code implement these checks with unsafe
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calculations on 32 and 64 bit values, which may allow a malicious
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guest to cause OOB access anyway.
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Fix this by comparing the offset and the xattr size, which are
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both uint64_t, before trying to compute the effective number of bytes
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to read or write.
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Suggested-by: Greg Kurz <groug@kaod.org>
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Signed-off-by: Li Qiang <liqiang6-s@360.cn>
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Reviewed-by: Greg Kurz <groug@kaod.org>
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Reviewed-By: Guido G√ľnther <agx@sigxcpu.org>
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Signed-off-by: Greg Kurz <groug@kaod.org>
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(cherry picked from commit 7e55d65c56a03dcd2c5d7c49d37c5a74b55d4bd6)
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---
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hw/9pfs/9p.c | 32 ++++++++++++--------------------
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1 file changed, 12 insertions(+), 20 deletions(-)
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diff --git a/hw/9pfs/9p.c b/hw/9pfs/9p.c
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index 22690f2..5126459 100644
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--- a/hw/9pfs/9p.c
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+++ b/hw/9pfs/9p.c
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@@ -1627,20 +1627,17 @@ static int v9fs_xattr_read(V9fsState *s, V9fsPDU *pdu, V9fsFidState *fidp,
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{
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ssize_t err;
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size_t offset = 7;
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- int read_count;
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- int64_t xattr_len;
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+ uint64_t read_count;
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V9fsVirtioState *v = container_of(s, V9fsVirtioState, state);
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VirtQueueElement *elem = v->elems[pdu->idx];
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- xattr_len = fidp->fs.xattr.len;
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- read_count = xattr_len - off;
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+ if (fidp->fs.xattr.len < off) {
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+ read_count = 0;
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+ } else {
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+ read_count = fidp->fs.xattr.len - off;
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+ }
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if (read_count > max_count) {
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read_count = max_count;
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- } else if (read_count < 0) {
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- /*
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- * read beyond XATTR value
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- */
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- read_count = 0;
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}
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err = pdu_marshal(pdu, offset, "d", read_count);
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if (err < 0) {
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@@ -1959,23 +1956,18 @@ static int v9fs_xattr_write(V9fsState *s, V9fsPDU *pdu, V9fsFidState *fidp,
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{
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int i, to_copy;
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ssize_t err = 0;
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- int write_count;
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- int64_t xattr_len;
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+ uint64_t write_count;
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size_t offset = 7;
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- xattr_len = fidp->fs.xattr.len;
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- write_count = xattr_len - off;
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- if (write_count > count) {
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- write_count = count;
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- } else if (write_count < 0) {
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- /*
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- * write beyond XATTR value len specified in
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- * xattrcreate
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- */
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+ if (fidp->fs.xattr.len < off) {
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err = -ENOSPC;
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goto out;
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}
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+ write_count = fidp->fs.xattr.len - off;
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+ if (write_count > count) {
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+ write_count = count;
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+ }
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err = pdu_marshal(pdu, offset, "d", write_count);
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if (err < 0) {
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return err;
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