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Use SCMP_CMP_MASKED_EQ to allow flags, not force them

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Older versions of Libevent are happy to open SOCK_DGRAM sockets
non-cloexec and non-nonblocking, and then set those flags
afterwards. It's nice to be able to allow a flag to be on or off in
the sandbox without having to enumerate all its values.

Also, permit PF_INET6 sockets. (D'oh!)
This commit is contained in:
Nick Mathewson 2014-04-16 15:17:23 -04:00
parent ce776cf270
commit 69eb278830
1 changed files with 26 additions and 27 deletions
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53
src/common/sandbox.c
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@ -77,6 +77,13 @@ static sb_addr_info_t *sb_addr_info = NULL;
#undef SCMP_CMP #undef SCMP_CMP
#define SCMP_CMP(a,b,c) ((struct scmp_arg_cmp){(a),(b),(c),0}) #define SCMP_CMP(a,b,c) ((struct scmp_arg_cmp){(a),(b),(c),0})
#define SCMP_CMP4(a,b,c,d) ((struct scmp_arg_cmp){(a),(b),(c),(d)})
/* We use a wrapper here because these masked comparisons seem to be pretty
* verbose. Also, it's important to cast to scmp_datum_t before negating the
* mask, since otherwise the negation might get applied to a 32 bit value, and
* the high bits of the value might get masked out improperly. */
#define SCMP_CMP_MASKED(a,b,c) \
SCMP_CMP4((a), SCMP_CMP_MASKED_EQ, ~(scmp_datum_t)(b), (c))
/** Variable used for storing all syscall numbers that will be allowed with the /** Variable used for storing all syscall numbers that will be allowed with the
* stage 1 general Tor sandbox. * stage 1 general Tor sandbox.
@ -258,12 +265,7 @@ sb_accept4(scmp_filter_ctx ctx, sandbox_cfg_t *filter)
#endif #endif
rc = seccomp_rule_add_1(ctx, SCMP_ACT_ALLOW, SCMP_SYS(accept4), rc = seccomp_rule_add_1(ctx, SCMP_ACT_ALLOW, SCMP_SYS(accept4),
SCMP_CMP(3, SCMP_CMP_EQ, SOCK_CLOEXEC)); SCMP_CMP_MASKED(3, SOCK_CLOEXEC|SOCK_NONBLOCK, 0));
if (rc) {
return rc;
}
rc = seccomp_rule_add_1(ctx, SCMP_ACT_ALLOW, SCMP_SYS(accept4),
SCMP_CMP(3, SCMP_CMP_EQ, SOCK_CLOEXEC|SOCK_NONBLOCK));
if (rc) { if (rc) {
return rc; return rc;
} }
@ -362,7 +364,7 @@ sb_open(scmp_filter_ctx ctx, sandbox_cfg_t *filter)
} }
rc = seccomp_rule_add_1(ctx, SCMP_ACT_ERRNO(-1), SCMP_SYS(open), rc = seccomp_rule_add_1(ctx, SCMP_ACT_ERRNO(-1), SCMP_SYS(open),
SCMP_CMP(1, SCMP_CMP_EQ, O_RDONLY|O_CLOEXEC)); SCMP_CMP_MASKED(1, O_CLOEXEC, O_RDONLY));
if (rc != 0) { if (rc != 0) {
log_err(LD_BUG,"(Sandbox) failed to add open syscall, received libseccomp " log_err(LD_BUG,"(Sandbox) failed to add open syscall, received libseccomp "
"error %d", rc); "error %d", rc);
@ -460,6 +462,7 @@ static int
sb_socket(scmp_filter_ctx ctx, sandbox_cfg_t *filter) sb_socket(scmp_filter_ctx ctx, sandbox_cfg_t *filter)
{ {
int rc = 0; int rc = 0;
int i;
(void) filter; (void) filter;
#ifdef __i386__ #ifdef __i386__
@ -468,33 +471,29 @@ sb_socket(scmp_filter_ctx ctx, sandbox_cfg_t *filter)
return rc; return rc;
#endif #endif
rc = seccomp_rule_add_3(ctx, SCMP_ACT_ALLOW, SCMP_SYS(socket), rc = seccomp_rule_add_2(ctx, SCMP_ACT_ALLOW, SCMP_SYS(socket),
SCMP_CMP(0, SCMP_CMP_EQ, PF_FILE), SCMP_CMP(0, SCMP_CMP_EQ, PF_FILE),
SCMP_CMP(1, SCMP_CMP_EQ, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK), SCMP_CMP_MASKED(1, SOCK_CLOEXEC|SOCK_NONBLOCK, SOCK_STREAM));
SCMP_CMP(2, SCMP_CMP_EQ, IPPROTO_IP));
if (rc) if (rc)
return rc; return rc;
rc = seccomp_rule_add_3(ctx, SCMP_ACT_ALLOW, SCMP_SYS(socket), for (i = 0; i < 2; ++i) {
SCMP_CMP(0, SCMP_CMP_EQ, PF_INET), const int pf = i ? PF_INET : PF_INET6;
SCMP_CMP(1, SCMP_CMP_EQ, SOCK_STREAM|SOCK_CLOEXEC),
rc = seccomp_rule_add_3(ctx, SCMP_ACT_ALLOW, SCMP_SYS(socket),
SCMP_CMP(0, SCMP_CMP_EQ, pf),
SCMP_CMP_MASKED(1, SOCK_CLOEXEC|SOCK_NONBLOCK, SOCK_STREAM),
SCMP_CMP(2, SCMP_CMP_EQ, IPPROTO_TCP)); SCMP_CMP(2, SCMP_CMP_EQ, IPPROTO_TCP));
if (rc) if (rc)
return rc; return rc;
rc = seccomp_rule_add_3(ctx, SCMP_ACT_ALLOW, SCMP_SYS(socket), rc = seccomp_rule_add_3(ctx, SCMP_ACT_ALLOW, SCMP_SYS(socket),
SCMP_CMP(0, SCMP_CMP_EQ, PF_INET), SCMP_CMP(0, SCMP_CMP_EQ, pf),
SCMP_CMP(1, SCMP_CMP_EQ, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK), SCMP_CMP_MASKED(1, SOCK_CLOEXEC|SOCK_NONBLOCK, SOCK_DGRAM),
SCMP_CMP(2, SCMP_CMP_EQ, IPPROTO_TCP));
if (rc)
return rc;
rc = seccomp_rule_add_3(ctx, SCMP_ACT_ALLOW, SCMP_SYS(socket),
SCMP_CMP(0, SCMP_CMP_EQ, PF_INET),
SCMP_CMP(1, SCMP_CMP_EQ, SOCK_DGRAM|SOCK_CLOEXEC|SOCK_NONBLOCK),
SCMP_CMP(2, SCMP_CMP_EQ, IPPROTO_IP)); SCMP_CMP(2, SCMP_CMP_EQ, IPPROTO_IP));
if (rc) if (rc)
return rc; return rc;
}
rc = seccomp_rule_add_3(ctx, SCMP_ACT_ALLOW, SCMP_SYS(socket), rc = seccomp_rule_add_3(ctx, SCMP_ACT_ALLOW, SCMP_SYS(socket),
SCMP_CMP(0, SCMP_CMP_EQ, PF_NETLINK), SCMP_CMP(0, SCMP_CMP_EQ, PF_NETLINK),