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[Qemu-devel] [PULL 3/7] 9pfs: fix integer overflow issue in xattr read/w
From: |
Greg Kurz |
Subject: |
[Qemu-devel] [PULL 3/7] 9pfs: fix integer overflow issue in xattr read/write |
Date: |
Sun, 30 Oct 2016 13:34:24 +0100 |
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>
Reviewed-by: Greg Kurz <address@hidden>
Reviewed-By: Guido Günther <address@hidden>
---
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 ab18ef2adf32..7705ead4b2ac 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;
--
2.5.5
- [Qemu-devel] [PULL 0/7] 9p patches for 2.8 20161030, Greg Kurz, 2016/10/30
- [Qemu-devel] [PULL 3/7] 9pfs: fix integer overflow issue in xattr read/write,
Greg Kurz <=
- [Qemu-devel] [PULL 2/7] 9pfs: convert 'len/copied_len' field in V9fsXattr to the type of uint64_t, Greg Kurz, 2016/10/30
- [Qemu-devel] [PULL 1/7] 9pfs: add xattrwalk_fid field in V9fsXattr struct, Greg Kurz, 2016/10/30
- [Qemu-devel] [PULL 4/7] 9pfs: limit xattr size in xattrcreate, Greg Kurz, 2016/10/30
- [Qemu-devel] [PULL 5/7] 9pfs: xattrcreate requires non-opened fids, Greg Kurz, 2016/10/30
- [Qemu-devel] [PULL 6/7] 9pfs: don't BUG_ON() if fid is already opened, Greg Kurz, 2016/10/30
- [Qemu-devel] [PULL 7/7] 9pfs: drop excessive error message from virtfs_reset(), Greg Kurz, 2016/10/30
- Re: [Qemu-devel] [PULL 0/7] 9p patches for 2.8 20161030, Peter Maydell, 2016/10/31