From 56af94aace8a0489fb1a32fd6f1cf0c548fe3911 Mon Sep 17 00:00:00 2001 From: Arnd Bergmann Date: Mon, 12 Feb 2024 12:17:31 +0100 Subject: [PATCH] samples: user-trap: fix strict-aliasing warning I started getting warnings for this one file, though I can't see what changed since it was originally introduced in commit fec7b6690541 ("samples: add an example of seccomp user trap"). samples/seccomp/user-trap.c: In function 'send_fd': samples/seccomp/user-trap.c:50:11: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing] 50 | *((int *)CMSG_DATA(cmsg)) = fd; | ~^~~~~~~~~~~~~~~~~~~~~~~ samples/seccomp/user-trap.c: In function 'recv_fd': samples/seccomp/user-trap.c:83:18: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing] 83 | return *((int *)CMSG_DATA(cmsg)); | ~^~~~~~~~~~~~~~~~~~~~~~~ Using a temporary pointer variable avoids the warning. Signed-off-by: Arnd Bergmann Link: https://lore.kernel.org/r/20240212111737.917428-1-arnd@kernel.org Acked-by: Tycho Andersen Signed-off-by: Kees Cook --- samples/seccomp/user-trap.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/samples/seccomp/user-trap.c b/samples/seccomp/user-trap.c index 20291ec6489f..a23fec357b5d 100644 --- a/samples/seccomp/user-trap.c +++ b/samples/seccomp/user-trap.c @@ -33,6 +33,7 @@ static int send_fd(int sock, int fd) { struct msghdr msg = {}; struct cmsghdr *cmsg; + int *fd_ptr; char buf[CMSG_SPACE(sizeof(int))] = {0}, c = 'c'; struct iovec io = { .iov_base = &c, @@ -47,7 +48,8 @@ static int send_fd(int sock, int fd) cmsg->cmsg_level = SOL_SOCKET; cmsg->cmsg_type = SCM_RIGHTS; cmsg->cmsg_len = CMSG_LEN(sizeof(int)); - *((int *)CMSG_DATA(cmsg)) = fd; + fd_ptr = (int *)CMSG_DATA(cmsg); + *fd_ptr = fd; msg.msg_controllen = cmsg->cmsg_len; if (sendmsg(sock, &msg, 0) < 0) { @@ -62,6 +64,7 @@ static int recv_fd(int sock) { struct msghdr msg = {}; struct cmsghdr *cmsg; + int *fd_ptr; char buf[CMSG_SPACE(sizeof(int))] = {0}, c = 'c'; struct iovec io = { .iov_base = &c, @@ -79,8 +82,9 @@ static int recv_fd(int sock) } cmsg = CMSG_FIRSTHDR(&msg); + fd_ptr = (int *)CMSG_DATA(cmsg); - return *((int *)CMSG_DATA(cmsg)); + return *fd_ptr; } static int user_trap_syscall(int nr, unsigned int flags)