From fd8756fa1487577535d6294ae7cc67888b19ae2a Mon Sep 17 00:00:00 2001 From: Jori Koolstra Date: Thu, 13 Aug 2026 12:28:17 -0400 Subject: net: af_unix: useful handling of LSM denials on SCM_RIGHTS Right now if some LSM such as Smack denies an AF_UNIX socket peer to receive an SCM_RIGHTS fd, the SCM_RIGHTS fd array will be cut short at that point, and MSG_CTRUNC is set on return of recvmsg(). This is highly problematic behaviour, because it leaves the receiver wondering what happened. As per man page MSG_CTRUNC is supposed to indicate that the control buffer was sized too short, but suddenly a permission error might result in the exact same flag being set. Moreover, the receiver has no chance to determine how many fds got originally sent and how many were suppressed.[1] Add a SO_RIGHTS_NOTRUNC option to UNIX sockets to enable more useful handling of LSM denials when receiving SCM_RIGHTS messages: instead of truncating the message at the first blocked fd, keep every fd slot and store the LSM errno in the blocked slot. The socket option is inherited by the child accept() socket if set on the listen() socket. [1]: https://github.com/uapi-group/kernel-features#useful-handling-of-lsm-denials-on-scm_rights Reviewed-by: Christian Brauner (Amutable) Signed-off-by: Jori Koolstra Link: https://patch.msgid.link/20260813162818.149248-4-jkoolstra@xs4all.nl Signed-off-by: Jakub Kicinski --- arch/alpha/include/uapi/asm/socket.h | 2 ++ arch/mips/include/uapi/asm/socket.h | 2 ++ arch/parisc/include/uapi/asm/socket.h | 2 ++ arch/sparc/include/uapi/asm/socket.h | 2 ++ 4 files changed, 8 insertions(+) (limited to 'arch') diff --git a/arch/alpha/include/uapi/asm/socket.h b/arch/alpha/include/uapi/asm/socket.h index 5ef57f88df6b..946a5fad2691 100644 --- a/arch/alpha/include/uapi/asm/socket.h +++ b/arch/alpha/include/uapi/asm/socket.h @@ -155,6 +155,8 @@ #define SO_INQ 84 #define SCM_INQ SO_INQ +#define SO_RIGHTS_NOTRUNC 85 + #if !defined(__KERNEL__) #if __BITS_PER_LONG == 64 diff --git a/arch/mips/include/uapi/asm/socket.h b/arch/mips/include/uapi/asm/socket.h index 72fb1b006da9..f1641dde135f 100644 --- a/arch/mips/include/uapi/asm/socket.h +++ b/arch/mips/include/uapi/asm/socket.h @@ -166,6 +166,8 @@ #define SO_INQ 84 #define SCM_INQ SO_INQ +#define SO_RIGHTS_NOTRUNC 85 + #if !defined(__KERNEL__) #if __BITS_PER_LONG == 64 diff --git a/arch/parisc/include/uapi/asm/socket.h b/arch/parisc/include/uapi/asm/socket.h index c16ec36dfee6..f3a3815c7dc2 100644 --- a/arch/parisc/include/uapi/asm/socket.h +++ b/arch/parisc/include/uapi/asm/socket.h @@ -147,6 +147,8 @@ #define SO_INQ 0x4052 #define SCM_INQ SO_INQ +#define SO_RIGHTS_NOTRUNC 0x4053 + #if !defined(__KERNEL__) #if __BITS_PER_LONG == 64 diff --git a/arch/sparc/include/uapi/asm/socket.h b/arch/sparc/include/uapi/asm/socket.h index 71befa109e1c..7907f3b1f0ee 100644 --- a/arch/sparc/include/uapi/asm/socket.h +++ b/arch/sparc/include/uapi/asm/socket.h @@ -148,6 +148,8 @@ #define SO_INQ 0x005d #define SCM_INQ SO_INQ +#define SO_RIGHTS_NOTRUNC 0x005e + #if !defined(__KERNEL__) -- cgit v1.2.3