From: Menglong Dong <dong.mengl...@zte.com.cn>
Currently, MSG_CMSG_COMPAT is defined as '1 << 31'. However, 'msg_flags'
is defined with type of 'int' somewhere, such as 'packet_recvmsg' and
other recvmsg functions:
static int packet_recvmsg(struct socket *sock, struct msghdr *msg,
size_t len,
int flags)
If MSG_CMSG_COMPAT is set in 'flags', it's value will be negative.
Once it perform bit operations with MSG_*, the upper 32 bits of
the result will be set, just like what Guenter Roeck explained
here:
https://lore.kernel.org/netdev/20210317013758.ga134...@roeck-us.net
As David Laight suggested, fix this by change MSG_CMSG_COMPAT to
some value else. MSG_CMSG_COMPAT is an internal value, which is't
used in userspace, so this change works.
Reported-by: Guenter Roeck <li...@roeck-us.net>
Signed-off-by: Menglong Dong <dong.mengl...@zte.com.cn>
---
v2:
- add comment to stop people from trying to use BIT(31)
---
include/linux/socket.h | 14 +++++++++-----
1 file changed, 9 insertions(+), 5 deletions(-)
diff --git a/include/linux/socket.h b/include/linux/socket.h
index d5ebfe30d96b..61b2694d68dd 100644
--- a/include/linux/socket.h
+++ b/include/linux/socket.h
@@ -312,17 +312,21 @@ struct ucred {
* plain text and require encryption
*/
+#if defined(CONFIG_COMPAT)
+#define MSG_CMSG_COMPAT BIT(21) /* This message needs 32 bit
fixups */
+#else
+#define MSG_CMSG_COMPAT 0 /* We never have 32 bit fixups
*/
+#endif
+
#define MSG_ZEROCOPY BIT(26) /* Use user data in kernel path */
#define MSG_FASTOPEN BIT(29) /* Send data in TCP SYN */
#define MSG_CMSG_CLOEXEC BIT(30) /* Set close_on_exec for file
* descriptor received through
* SCM_RIGHTS
*/
-#if defined(CONFIG_COMPAT)
-#define MSG_CMSG_COMPAT BIT(31) /* This message needs 32 bit
fixups */
-#else
-#define MSG_CMSG_COMPAT 0 /* We never have 32 bit fixups
*/
-#endif
+/* Attention: Don't use BIT(31) for MSG_*, as 'msg_flags' is defined
+ * as 'int' somewhere and BIT(31) will make it become negative.
+ */
/* Setsockoptions(2) level. Thanks to BSD these must match IPPROTO_xxx */
--
2.31.0
