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[Qemu-devel] [PATCH v3 3/3] 9pfs: fix integer overflow issue in xattr re
From: |
Li Qiang |
Subject: |
[Qemu-devel] [PATCH v3 3/3] 9pfs: fix integer overflow issue in xattr read/write |
Date: |
Thu, 13 Oct 2016 03:09:43 -0700 |
From: Li Qiang <address@hidden>
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 <address@hidden>
Signed-off-by: Li Qiang <address@hidden>
---
Changes since v2:
-make the solution of 'copied_len/len' in V9fsXattr type issue to a separate
patch.
-add detailed changelog.
Changes since v1:
-delete 'xattr_len'.
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 e902eed..6df85b8 100644
--- a/hw/9pfs/9p.c
+++ b/hw/9pfs/9p.c
@@ -1642,20 +1642,17 @@ 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) {
@@ -1982,23 +1979,18 @@ 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;
--
1.8.3.1
- [Qemu-devel] [PATCH v3 3/3] 9pfs: fix integer overflow issue in xattr read/write,
Li Qiang <=