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Tighten seccomp sandbox restrictions on mmap(), ioctl() and socketcall()
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@ -7,11 +7,15 @@
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#include <sys/prctl.h>
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#include <sys/ptrace.h>
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#include <sys/mman.h> // for mmap() args
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#include <sys/ioctl.h> // for ioctl() args
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#include <termios.h> // for ioctl() args
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#include <linux/unistd.h>
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#include <linux/seccomp.h>
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#include <linux/filter.h>
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#include <linux/audit.h>
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#include <linux/net.h> // for socketcall() args
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// our own wrapper for the seccomp() syscall
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// TODO: should this be conditional on a feature check or something?
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@ -52,6 +56,57 @@ static inline int seccomp(unsigned int operation, unsigned int flags, void *args
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#define KILL_PROCESS \
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BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_KILL)
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/*
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* Macros adapted from openssh's sandbox-seccomp-filter.c
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* Relevant license:
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* https://github.com/openssh/openssh-portable/blob/master/LICENCE
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*/
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#if __BYTE_ORDER == __LITTLE_ENDIAN
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# define ARG_LO_OFFSET 0
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# define ARG_HI_OFFSET sizeof(uint32_t)
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#elif __BYTE_ORDER == __BIG_ENDIAN
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# define ARG_LO_OFFSET sizeof(uint32_t)
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# define ARG_HI_OFFSET 0
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#else
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#error "Unknown endianness"
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#endif
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#define ALLOW_SYSCALL_ARG(_nr, _arg_nr, _arg_val) \
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BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (__NR_##_nr), 0, 6), \
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/* load and test syscall argument, low word */ \
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BPF_STMT(BPF_LD+BPF_W+BPF_ABS, \
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offsetof(struct seccomp_data, args[(_arg_nr)]) + ARG_LO_OFFSET), \
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BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, \
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((_arg_val) & 0xFFFFFFFF), 0, 3), \
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/* load and test syscall argument, high word */ \
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BPF_STMT(BPF_LD+BPF_W+BPF_ABS, \
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offsetof(struct seccomp_data, args[(_arg_nr)]) + ARG_HI_OFFSET), \
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BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, \
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(((uint32_t)((uint64_t)(_arg_val) >> 32)) & 0xFFFFFFFF), 0, 1), \
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BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ALLOW), \
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/* reload syscall number; all rules expect it in accumulator */ \
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BPF_STMT(BPF_LD+BPF_W+BPF_ABS, \
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offsetof(struct seccomp_data, nr))
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/* Allow if syscall argument contains only values in mask */
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#define ALLOW_SYSCALL_ARG_MASK(_nr, _arg_nr, _arg_mask) \
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BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (__NR_##_nr), 0, 8), \
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/* load, mask and test syscall argument, low word */ \
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BPF_STMT(BPF_LD+BPF_W+BPF_ABS, \
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offsetof(struct seccomp_data, args[(_arg_nr)]) + ARG_LO_OFFSET), \
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BPF_STMT(BPF_ALU+BPF_AND+BPF_K, ~((_arg_mask) & 0xFFFFFFFF)), \
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BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, 0, 0, 4), \
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/* load, mask and test syscall argument, high word */ \
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BPF_STMT(BPF_LD+BPF_W+BPF_ABS, \
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offsetof(struct seccomp_data, args[(_arg_nr)]) + ARG_HI_OFFSET), \
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BPF_STMT(BPF_ALU+BPF_AND+BPF_K, \
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~(((uint32_t)((uint64_t)(_arg_mask) >> 32)) & 0xFFFFFFFF)), \
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BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, 0, 0, 1), \
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BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ALLOW), \
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/* reload syscall number; all rules expect it in accumulator */ \
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BPF_STMT(BPF_LD+BPF_W+BPF_ABS, \
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offsetof(struct seccomp_data, nr))
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/*
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* The main supported configuration is Linux on x86_64 with either glibc or
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* musl-libc, with secondary support for Linux on the Raspberry Pi (ARM).
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@ -74,10 +129,10 @@ static sock_filter filter[] = {
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// memory management
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#ifdef __NR_mmap
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ALLOW_SYSCALL(mmap),
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ALLOW_SYSCALL_ARG_MASK(mmap, 2, PROT_NONE|PROT_READ|PROT_WRITE),
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#endif
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ALLOW_SYSCALL(munmap),
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ALLOW_SYSCALL(mprotect),
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ALLOW_SYSCALL_ARG_MASK(mprotect, 2, PROT_NONE|PROT_READ|PROT_WRITE),
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ALLOW_SYSCALL(madvise),
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ALLOW_SYSCALL(brk),
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@ -93,6 +148,7 @@ static sock_filter filter[] = {
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ALLOW_SYSCALL(creat), // maybe; for DB journal
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ALLOW_SYSCALL(unlink), // for DB journal
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ALLOW_SYSCALL(lseek), // musl-libc; alt DB
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ALLOW_SYSCALL(dup), // for perror(), apparently
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// more IO
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ALLOW_SYSCALL(pread64),
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@ -106,7 +162,8 @@ static sock_filter filter[] = {
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ALLOW_SYSCALL(getcwd),
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ALLOW_SYSCALL(getpid),
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ALLOW_SYSCALL(geteuid),
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ALLOW_SYSCALL(ioctl), // musl-libc
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ALLOW_SYSCALL(gettid), // maybe
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ALLOW_SYSCALL_ARG(ioctl, 1, TIOCGWINSZ), // musl-libc
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ALLOW_SYSCALL(fcntl),
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ALLOW_SYSCALL(exit),
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ALLOW_SYSCALL(exit_group),
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@ -135,7 +192,13 @@ static sock_filter filter[] = {
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// i386
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#ifdef __NR_socketcall
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ALLOW_SYSCALL(socketcall),
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ALLOW_SYSCALL_ARG(socketcall, 0, SYS_ACCEPT),
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ALLOW_SYSCALL_ARG(socketcall, 0, SYS_SETSOCKOPT),
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ALLOW_SYSCALL_ARG(socketcall, 0, SYS_SEND),
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ALLOW_SYSCALL_ARG(socketcall, 0, SYS_RECV),
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ALLOW_SYSCALL_ARG(socketcall, 0, SYS_SENDTO), // maybe
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ALLOW_SYSCALL_ARG(socketcall, 0, SYS_RECVFROM), // maybe
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ALLOW_SYSCALL_ARG(socketcall, 0, SYS_SHUTDOWN),
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#endif
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// Raspberry Pi (ARM)
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@ -146,7 +209,7 @@ static sock_filter filter[] = {
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ALLOW_SYSCALL(clock_gettime64),
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#endif
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#ifdef __NR_mmap2
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ALLOW_SYSCALL(mmap2),
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ALLOW_SYSCALL_ARG_MASK(mmap2, 2, PROT_NONE|PROT_READ|PROT_WRITE),
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#endif
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#ifdef __NR_fcntl64
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ALLOW_SYSCALL(fcntl64),
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