Syzkaller reports refcount bug as follows:
------------[ cut here ]------------
memcpy: detected field-spanning write (size 8) of single field
"&compat_event->pointer" at net/wireless/wext-core.c:623 (size 4)
WARNING: CPU: 0 PID: 3607 at net/wireless/wext-core.c:623
wireless_send_event+0xab5/0xca0 net/wireless/wext-core.c:623
Modules linked in:
CPU: 1 PID: 3607 Comm: syz-executor659 Not tainted
6.0.0-rc6-next-20220921-syzkaller #0
[...]
Call Trace:
<TASK>
ioctl_standard_call+0x155/0x1f0 net/wireless/wext-core.c:1022
wireless_process_ioctl+0xc8/0x4c0 net/wireless/wext-core.c:955
wext_ioctl_dispatch net/wireless/wext-core.c:988 [inline]
wext_ioctl_dispatch net/wireless/wext-core.c:976 [inline]
wext_handle_ioctl+0x26b/0x280 net/wireless/wext-core.c:1049
sock_ioctl+0x285/0x640 net/socket.c:1220
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:870 [inline]
__se_sys_ioctl fs/ioctl.c:856 [inline]
__x64_sys_ioctl+0x193/0x200 fs/ioctl.c:856
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd
[...]
</TASK>
Wireless events will be sent on the appropriate channels in
wireless_send_event(). Different wireless events may have different
payload structure and size, so kernel uses **len** and **cmd** field
in struct __compat_iw_event as wireless event common LCP part, uses
**pointer** as a label to mark the position of remaining different part.
Yet the problem is that, **pointer** is a compat_caddr_t type, which may
be smaller than the relative structure at the same position. So during
wireless_send_event() tries to parse the wireless events payload, it may
trigger the memcpy() run-time destination buffer bounds checking when the
relative structure's data is copied to the position marked by **pointer**.
This patch solves it by introducing flexible-array field **ptr_bytes**,
to mark the position of the wireless events remaining part next to
LCP part. What's more, this patch also adds **ptr_len** variable in
wireless_send_event() to improve its maintainability.
Reported-and-tested-by: [email protected]
Link: https://lore.kernel.org/all/[email protected]/
Suggested-by: Kees Cook <[email protected]>
Signed-off-by: Hawkins Jiawei <[email protected]>
---
include/linux/wireless.h | 10 +++++++++-
net/wireless/wext-core.c | 17 ++++++++++-------
2 files changed, 19 insertions(+), 8 deletions(-)
diff --git a/include/linux/wireless.h b/include/linux/wireless.h
index 2d1b54556eff..e6e34d74dda0 100644
--- a/include/linux/wireless.h
+++ b/include/linux/wireless.h
@@ -26,7 +26,15 @@ struct compat_iw_point {
struct __compat_iw_event {
__u16 len; /* Real length of this stuff */
__u16 cmd; /* Wireless IOCTL */
- compat_caddr_t pointer;
+
+ union {
+ compat_caddr_t pointer;
+
+ /* we need ptr_bytes to make memcpy() run-time destination
+ * buffer bounds checking happy, nothing special
+ */
+ DECLARE_FLEX_ARRAY(__u8, ptr_bytes);
+ };
};
#define IW_EV_COMPAT_LCP_LEN offsetof(struct __compat_iw_event, pointer)
#define IW_EV_COMPAT_POINT_OFF offsetof(struct compat_iw_point, length)
diff --git a/net/wireless/wext-core.c b/net/wireless/wext-core.c
index 76a80a41615b..fe8765c4075d 100644
--- a/net/wireless/wext-core.c
+++ b/net/wireless/wext-core.c
@@ -468,6 +468,7 @@ void wireless_send_event(struct net_device * dev,
struct __compat_iw_event *compat_event;
struct compat_iw_point compat_wrqu;
struct sk_buff *compskb;
+ int ptr_len;
#endif
/*
@@ -582,6 +583,9 @@ void wireless_send_event(struct net_device * dev,
nlmsg_end(skb, nlh);
#ifdef CONFIG_COMPAT
hdr_len = compat_event_type_size[descr->header_type];
+
+ /* ptr_len is remaining size in event header apart from LCP */
+ ptr_len = hdr_len - IW_EV_COMPAT_LCP_LEN;
event_len = hdr_len + extra_len;
compskb = nlmsg_new(NLMSG_DEFAULT_SIZE, GFP_ATOMIC);
@@ -612,16 +616,15 @@ void wireless_send_event(struct net_device * dev,
if (descr->header_type == IW_HEADER_TYPE_POINT) {
compat_wrqu.length = wrqu->data.length;
compat_wrqu.flags = wrqu->data.flags;
- memcpy(&compat_event->pointer,
- ((char *) &compat_wrqu) + IW_EV_COMPAT_POINT_OFF,
- hdr_len - IW_EV_COMPAT_LCP_LEN);
+ memcpy(compat_event->ptr_bytes,
+ ((char *)&compat_wrqu) + IW_EV_COMPAT_POINT_OFF,
+ ptr_len);
if (extra_len)
- memcpy(((char *) compat_event) + hdr_len,
- extra, extra_len);
+ memcpy(&compat_event->ptr_bytes[ptr_len],
+ extra, extra_len);
} else {
/* extra_len must be zero, so no if (extra) needed */
- memcpy(&compat_event->pointer, wrqu,
- hdr_len - IW_EV_COMPAT_LCP_LEN);
+ memcpy(compat_event->ptr_bytes, wrqu, ptr_len);
}
nlmsg_end(compskb, nlh);
--
2.25.1
On Mon, Sep 26, 2022 at 8:09 AM Hawkins Jiawei <[email protected]> wrote:
>
> Syzkaller reports refcount bug as follows:
This has nothing to do with a refcount bug...
> ------------[ cut here ]------------
> memcpy: detected field-spanning write (size 8) of single field
> "&compat_event->pointer" at net/wireless/wext-core.c:623 (size 4)
> WARNING: CPU: 0 PID: 3607 at net/wireless/wext-core.c:623
> wireless_send_event+0xab5/0xca0 net/wireless/wext-core.c:623
> Modules linked in:
> CPU: 1 PID: 3607 Comm: syz-executor659 Not tainted
> 6.0.0-rc6-next-20220921-syzkaller #0
> [...]
> Call Trace:
> <TASK>
> ioctl_standard_call+0x155/0x1f0 net/wireless/wext-core.c:1022
> wireless_process_ioctl+0xc8/0x4c0 net/wireless/wext-core.c:955
> wext_ioctl_dispatch net/wireless/wext-core.c:988 [inline]
> wext_ioctl_dispatch net/wireless/wext-core.c:976 [inline]
> wext_handle_ioctl+0x26b/0x280 net/wireless/wext-core.c:1049
> sock_ioctl+0x285/0x640 net/socket.c:1220
> vfs_ioctl fs/ioctl.c:51 [inline]
> __do_sys_ioctl fs/ioctl.c:870 [inline]
> __se_sys_ioctl fs/ioctl.c:856 [inline]
> __x64_sys_ioctl+0x193/0x200 fs/ioctl.c:856
> do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
> entry_SYSCALL_64_after_hwframe+0x63/0xcd
> [...]
> </TASK>
>
> Wireless events will be sent on the appropriate channels in
> wireless_send_event(). Different wireless events may have different
> payload structure and size, so kernel uses **len** and **cmd** field
> in struct __compat_iw_event as wireless event common LCP part, uses
> **pointer** as a label to mark the position of remaining different part.
>
> Yet the problem is that, **pointer** is a compat_caddr_t type, which may
> be smaller than the relative structure at the same position. So during
> wireless_send_event() tries to parse the wireless events payload, it may
> trigger the memcpy() run-time destination buffer bounds checking when the
> relative structure's data is copied to the position marked by **pointer**.
>
> This patch solves it by introducing flexible-array field **ptr_bytes**,
> to mark the position of the wireless events remaining part next to
> LCP part. What's more, this patch also adds **ptr_len** variable in
> wireless_send_event() to improve its maintainability.
>
> Reported-and-tested-by: [email protected]
> Link: https://lore.kernel.org/all/[email protected]/
> Suggested-by: Kees Cook <[email protected]>
> Signed-off-by: Hawkins Jiawei <[email protected]>
> ---
> include/linux/wireless.h | 10 +++++++++-
> net/wireless/wext-core.c | 17 ++++++++++-------
> 2 files changed, 19 insertions(+), 8 deletions(-)
>
> diff --git a/include/linux/wireless.h b/include/linux/wireless.h
> index 2d1b54556eff..e6e34d74dda0 100644
> --- a/include/linux/wireless.h
> +++ b/include/linux/wireless.h
> @@ -26,7 +26,15 @@ struct compat_iw_point {
> struct __compat_iw_event {
> __u16 len; /* Real length of this stuff */
> __u16 cmd; /* Wireless IOCTL */
> - compat_caddr_t pointer;
> +
> + union {
> + compat_caddr_t pointer;
> +
> + /* we need ptr_bytes to make memcpy() run-time destination
> + * buffer bounds checking happy, nothing special
> + */
> + DECLARE_FLEX_ARRAY(__u8, ptr_bytes);
> + };
> };
> #define IW_EV_COMPAT_LCP_LEN offsetof(struct __compat_iw_event, pointer)
> #define IW_EV_COMPAT_POINT_OFF offsetof(struct compat_iw_point, length)
> diff --git a/net/wireless/wext-core.c b/net/wireless/wext-core.c
> index 76a80a41615b..fe8765c4075d 100644
> --- a/net/wireless/wext-core.c
> +++ b/net/wireless/wext-core.c
> @@ -468,6 +468,7 @@ void wireless_send_event(struct net_device * dev,
> struct __compat_iw_event *compat_event;
> struct compat_iw_point compat_wrqu;
> struct sk_buff *compskb;
> + int ptr_len;
> #endif
>
> /*
> @@ -582,6 +583,9 @@ void wireless_send_event(struct net_device * dev,
> nlmsg_end(skb, nlh);
> #ifdef CONFIG_COMPAT
> hdr_len = compat_event_type_size[descr->header_type];
> +
> + /* ptr_len is remaining size in event header apart from LCP */
> + ptr_len = hdr_len - IW_EV_COMPAT_LCP_LEN;
> event_len = hdr_len + extra_len;
>
> compskb = nlmsg_new(NLMSG_DEFAULT_SIZE, GFP_ATOMIC);
> @@ -612,16 +616,15 @@ void wireless_send_event(struct net_device * dev,
> if (descr->header_type == IW_HEADER_TYPE_POINT) {
> compat_wrqu.length = wrqu->data.length;
> compat_wrqu.flags = wrqu->data.flags;
> - memcpy(&compat_event->pointer,
> - ((char *) &compat_wrqu) + IW_EV_COMPAT_POINT_OFF,
> - hdr_len - IW_EV_COMPAT_LCP_LEN);
> + memcpy(compat_event->ptr_bytes,
> + ((char *)&compat_wrqu) + IW_EV_COMPAT_POINT_OFF,
> + ptr_len);
> if (extra_len)
> - memcpy(((char *) compat_event) + hdr_len,
> - extra, extra_len);
> + memcpy(&compat_event->ptr_bytes[ptr_len],
> + extra, extra_len);
> } else {
> /* extra_len must be zero, so no if (extra) needed */
> - memcpy(&compat_event->pointer, wrqu,
> - hdr_len - IW_EV_COMPAT_LCP_LEN);
> + memcpy(compat_event->ptr_bytes, wrqu, ptr_len);
> }
>
> nlmsg_end(compskb, nlh);
> --
> 2.25.1
>
On Mon, Sep 26, 2022 at 11:09:06PM +0800, Hawkins Jiawei wrote:
> Syzkaller reports refcount bug as follows:
"buffer overflow false positive" instead of "refcount bug"
> ------------[ cut here ]------------
> memcpy: detected field-spanning write (size 8) of single field
> "&compat_event->pointer" at net/wireless/wext-core.c:623 (size 4)
> WARNING: CPU: 0 PID: 3607 at net/wireless/wext-core.c:623
> wireless_send_event+0xab5/0xca0 net/wireless/wext-core.c:623
> Modules linked in:
> CPU: 1 PID: 3607 Comm: syz-executor659 Not tainted
> 6.0.0-rc6-next-20220921-syzkaller #0
> [...]
> Call Trace:
> <TASK>
> ioctl_standard_call+0x155/0x1f0 net/wireless/wext-core.c:1022
> wireless_process_ioctl+0xc8/0x4c0 net/wireless/wext-core.c:955
> wext_ioctl_dispatch net/wireless/wext-core.c:988 [inline]
> wext_ioctl_dispatch net/wireless/wext-core.c:976 [inline]
> wext_handle_ioctl+0x26b/0x280 net/wireless/wext-core.c:1049
> sock_ioctl+0x285/0x640 net/socket.c:1220
> vfs_ioctl fs/ioctl.c:51 [inline]
> __do_sys_ioctl fs/ioctl.c:870 [inline]
> __se_sys_ioctl fs/ioctl.c:856 [inline]
> __x64_sys_ioctl+0x193/0x200 fs/ioctl.c:856
> do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
> entry_SYSCALL_64_after_hwframe+0x63/0xcd
> [...]
> </TASK>
>
> Wireless events will be sent on the appropriate channels in
> wireless_send_event(). Different wireless events may have different
> payload structure and size, so kernel uses **len** and **cmd** field
> in struct __compat_iw_event as wireless event common LCP part, uses
> **pointer** as a label to mark the position of remaining different part.
>
> Yet the problem is that, **pointer** is a compat_caddr_t type, which may
> be smaller than the relative structure at the same position. So during
> wireless_send_event() tries to parse the wireless events payload, it may
> trigger the memcpy() run-time destination buffer bounds checking when the
> relative structure's data is copied to the position marked by **pointer**.
>
> This patch solves it by introducing flexible-array field **ptr_bytes**,
> to mark the position of the wireless events remaining part next to
> LCP part. What's more, this patch also adds **ptr_len** variable in
> wireless_send_event() to improve its maintainability.
>
> Reported-and-tested-by: [email protected]
> Link: https://lore.kernel.org/all/[email protected]/
> Suggested-by: Kees Cook <[email protected]>
> Signed-off-by: Hawkins Jiawei <[email protected]>
Thanks for spinning this and getting it tested!
Reviewed-by: Kees Cook <[email protected]>
--
Kees Cook
On Tue, 27 Sept 2022 at 00:14, Eric Dumazet <[email protected]> wrote:
>
> On Mon, Sep 26, 2022 at 8:09 AM Hawkins Jiawei <[email protected]> wrote:
> >
> > Syzkaller reports refcount bug as follows:
>
> This has nothing to do with a refcount bug...
Sorry for my typo error, it should be a "buffer overflow false positive" bug
as Kees Cook points out.
I will correct it in my v2 patch.
>
> > ------------[ cut here ]------------
>
>
> > memcpy: detected field-spanning write (size 8) of single field
> > "&compat_event->pointer" at net/wireless/wext-core.c:623 (size 4)
> > WARNING: CPU: 0 PID: 3607 at net/wireless/wext-core.c:623
> > wireless_send_event+0xab5/0xca0 net/wireless/wext-core.c:623
> > Modules linked in:
> > CPU: 1 PID: 3607 Comm: syz-executor659 Not tainted
> > 6.0.0-rc6-next-20220921-syzkaller #0
> > [...]
> > Call Trace:
> > <TASK>
> > ioctl_standard_call+0x155/0x1f0 net/wireless/wext-core.c:1022
> > wireless_process_ioctl+0xc8/0x4c0 net/wireless/wext-core.c:955
> > wext_ioctl_dispatch net/wireless/wext-core.c:988 [inline]
> > wext_ioctl_dispatch net/wireless/wext-core.c:976 [inline]
> > wext_handle_ioctl+0x26b/0x280 net/wireless/wext-core.c:1049
> > sock_ioctl+0x285/0x640 net/socket.c:1220
> > vfs_ioctl fs/ioctl.c:51 [inline]
> > __do_sys_ioctl fs/ioctl.c:870 [inline]
> > __se_sys_ioctl fs/ioctl.c:856 [inline]
> > __x64_sys_ioctl+0x193/0x200 fs/ioctl.c:856
> > do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> > do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
> > entry_SYSCALL_64_after_hwframe+0x63/0xcd
> > [...]
> > </TASK>
> >
> > Wireless events will be sent on the appropriate channels in
> > wireless_send_event(). Different wireless events may have different
> > payload structure and size, so kernel uses **len** and **cmd** field
> > in struct __compat_iw_event as wireless event common LCP part, uses
> > **pointer** as a label to mark the position of remaining different part.
> >
> > Yet the problem is that, **pointer** is a compat_caddr_t type, which may
> > be smaller than the relative structure at the same position. So during
> > wireless_send_event() tries to parse the wireless events payload, it may
> > trigger the memcpy() run-time destination buffer bounds checking when the
> > relative structure's data is copied to the position marked by **pointer**.
> >
> > This patch solves it by introducing flexible-array field **ptr_bytes**,
> > to mark the position of the wireless events remaining part next to
> > LCP part. What's more, this patch also adds **ptr_len** variable in
> > wireless_send_event() to improve its maintainability.
> >
> > Reported-and-tested-by: [email protected]
> > Link: https://lore.kernel.org/all/[email protected]/
> > Suggested-by: Kees Cook <[email protected]>
> > Signed-off-by: Hawkins Jiawei <[email protected]>
> > ---
> > include/linux/wireless.h | 10 +++++++++-
> > net/wireless/wext-core.c | 17 ++++++++++-------
> > 2 files changed, 19 insertions(+), 8 deletions(-)
> >
> > diff --git a/include/linux/wireless.h b/include/linux/wireless.h
> > index 2d1b54556eff..e6e34d74dda0 100644
> > --- a/include/linux/wireless.h
> > +++ b/include/linux/wireless.h
> > @@ -26,7 +26,15 @@ struct compat_iw_point {
> > struct __compat_iw_event {
> > __u16 len; /* Real length of this stuff */
> > __u16 cmd; /* Wireless IOCTL */
> > - compat_caddr_t pointer;
> > +
> > + union {
> > + compat_caddr_t pointer;
> > +
> > + /* we need ptr_bytes to make memcpy() run-time destination
> > + * buffer bounds checking happy, nothing special
> > + */
> > + DECLARE_FLEX_ARRAY(__u8, ptr_bytes);
> > + };
> > };
> > #define IW_EV_COMPAT_LCP_LEN offsetof(struct __compat_iw_event, pointer)
> > #define IW_EV_COMPAT_POINT_OFF offsetof(struct compat_iw_point, length)
> > diff --git a/net/wireless/wext-core.c b/net/wireless/wext-core.c
> > index 76a80a41615b..fe8765c4075d 100644
> > --- a/net/wireless/wext-core.c
> > +++ b/net/wireless/wext-core.c
> > @@ -468,6 +468,7 @@ void wireless_send_event(struct net_device * dev,
> > struct __compat_iw_event *compat_event;
> > struct compat_iw_point compat_wrqu;
> > struct sk_buff *compskb;
> > + int ptr_len;
> > #endif
> >
> > /*
> > @@ -582,6 +583,9 @@ void wireless_send_event(struct net_device * dev,
> > nlmsg_end(skb, nlh);
> > #ifdef CONFIG_COMPAT
> > hdr_len = compat_event_type_size[descr->header_type];
> > +
> > + /* ptr_len is remaining size in event header apart from LCP */
> > + ptr_len = hdr_len - IW_EV_COMPAT_LCP_LEN;
> > event_len = hdr_len + extra_len;
> >
> > compskb = nlmsg_new(NLMSG_DEFAULT_SIZE, GFP_ATOMIC);
> > @@ -612,16 +616,15 @@ void wireless_send_event(struct net_device * dev,
> > if (descr->header_type == IW_HEADER_TYPE_POINT) {
> > compat_wrqu.length = wrqu->data.length;
> > compat_wrqu.flags = wrqu->data.flags;
> > - memcpy(&compat_event->pointer,
> > - ((char *) &compat_wrqu) + IW_EV_COMPAT_POINT_OFF,
> > - hdr_len - IW_EV_COMPAT_LCP_LEN);
> > + memcpy(compat_event->ptr_bytes,
> > + ((char *)&compat_wrqu) + IW_EV_COMPAT_POINT_OFF,
> > + ptr_len);
> > if (extra_len)
> > - memcpy(((char *) compat_event) + hdr_len,
> > - extra, extra_len);
> > + memcpy(&compat_event->ptr_bytes[ptr_len],
> > + extra, extra_len);
> > } else {
> > /* extra_len must be zero, so no if (extra) needed */
> > - memcpy(&compat_event->pointer, wrqu,
> > - hdr_len - IW_EV_COMPAT_LCP_LEN);
> > + memcpy(compat_event->ptr_bytes, wrqu, ptr_len);
> > }
> >
> > nlmsg_end(compskb, nlh);
> > --
> > 2.25.1
> >