[openssh-commits] [openssh] 02/06: allow some socket syscalls in seccomp sandbox

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djm pushed a commit to branch master
in repository openssh.

commit 3a039108bd25ff10047d7fa64750ed7df10c717c
Author: Damien Miller <djm at mindrot.org>
AuthorDate: Mon Aug 18 13:46:37 2025 +1000

    allow some socket syscalls in seccomp sandbox
    
    Allow getsockname(2), getpeername(2) and getsockopt(2).
    
    Also allow setsockopt(2) but only IP_TOS and IPV6_TCLASS.
    
    Note that systems that use the older socketcall(2) mux syscall will
    not have IP_TOS and IPV6_TCLASS allowlisted. On these platforms,
    these calls will be soft-blocked (i.e. will fail rather than
    terminate the whole process with a sandbox violation).
    
    Needed for upcoming IPQoS change; ok dtucker@
---
 sandbox-seccomp-filter.c | 44 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 44 insertions(+)

diff --git a/sandbox-seccomp-filter.c b/sandbox-seccomp-filter.c
index 827cb61ee..a8f34a76c 100644
--- a/sandbox-seccomp-filter.c
+++ b/sandbox-seccomp-filter.c
@@ -49,6 +49,8 @@
 #include <sys/mman.h>
 #include <sys/syscall.h>
 
+#include <netinet/ip.h>
+
 #include <linux/futex.h>
 #include <linux/net.h>
 #include <linux/audit.h>
@@ -200,6 +202,32 @@
 	SC_ALLOW_ARG_MASK(_nr, 2, PROT_READ|PROT_WRITE|PROT_NONE)
 #endif /* __NR_mmap || __NR_mmap2 */
 
+/* Special handling for setsockopt(2) */
+#define SC_ALLOW_SETSOCKOPT(_level, _optname) \
+	BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, __NR_setsockopt, 0, 10), \
+	/* load and test level, low word */ \
+	BPF_STMT(BPF_LD+BPF_W+BPF_ABS, \
+	    offsetof(struct seccomp_data, args[1]) + ARG_LO_OFFSET), \
+	BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, \
+	    ((_level) & 0xFFFFFFFF), 0, 7), \
+	/* load and test level high word is zero */ \
+	BPF_STMT(BPF_LD+BPF_W+BPF_ABS, \
+	    offsetof(struct seccomp_data, args[1]) + ARG_HI_OFFSET), \
+	BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, 0, 0, 5), \
+	/* load and test optname, low word */ \
+	BPF_STMT(BPF_LD+BPF_W+BPF_ABS, \
+	    offsetof(struct seccomp_data, args[2]) + ARG_LO_OFFSET), \
+	BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, \
+	    ((_optname) & 0xFFFFFFFF), 0, 3), \
+	/* load and test level high word is zero */ \
+	BPF_STMT(BPF_LD+BPF_W+BPF_ABS, \
+	    offsetof(struct seccomp_data, args[2]) + ARG_HI_OFFSET), \
+	BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, 0, 0, 1), \
+	BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ALLOW), \
+	/* reload syscall number; all rules expect it in accumulator */ \
+	BPF_STMT(BPF_LD+BPF_W+BPF_ABS, \
+		offsetof(struct seccomp_data, nr))
+
 /* Syscall filtering set for preauth. */
 static const struct sock_filter preauth_insns[] = {
 	/* Ensure the syscall arch convention is as expected. */
@@ -398,7 +426,23 @@ static const struct sock_filter preauth_insns[] = {
 #ifdef __NR_writev
 	SC_ALLOW(__NR_writev),
 #endif
+#ifdef __NR_getsockopt
+	SC_ALLOW(__NR_getsockopt),
+#endif
+#ifdef __NR_getsockname
+	SC_ALLOW(__NR_getsockname),
+#endif
+#ifdef __NR_getpeername
+	SC_ALLOW(__NR_getpeername),
+#endif
+#ifdef __NR_setsockopt
+	SC_ALLOW_SETSOCKOPT(IPPROTO_IPV6, IPV6_TCLASS),
+	SC_ALLOW_SETSOCKOPT(IPPROTO_IP, IP_TOS),
+#endif
 #ifdef __NR_socketcall
+	SC_ALLOW_ARG(__NR_socketcall, 0, SYS_GETPEERNAME),
+	SC_ALLOW_ARG(__NR_socketcall, 0, SYS_GETSOCKNAME),
+	SC_ALLOW_ARG(__NR_socketcall, 0, SYS_GETSOCKOPT),
 	SC_ALLOW_ARG(__NR_socketcall, 0, SYS_SHUTDOWN),
 	SC_DENY(__NR_socketcall, EACCES),
 #endif

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