From 51ddf61540976fc7b09ce5ace707b27f3acc3871 Mon Sep 17 00:00:00 2001 From: Zbigniew Jędrzejewski-Szmek Date: Sun, 1 Feb 2015 14:33:10 -0500 Subject: Fix dropping of all capabilities From fd.o bug 88898: systemd-resolved fails to start: Failed to drop capabilities: Operation not permitted Broken in f11943c53ec181829a821c6b27acf828bab71caa. Drop all capabilities: 1. prctl(PR_SET_KEEPCAPS, keep_capabilities != 0) // 0 when we drop all capabilities 2. setresuid() // bye bye capabilities 3. Add CAP_SETPCAP // fails because we have no capabilities 4. Reduce capability bounding set 5. Drop capabilities 6. prctl(PR_SET_KEEPCAPS, 0) Capabilites should always be kept after setresuid() so that the capability bounding set can be reduced. Based-on-a-patch-by: mustrumr97@gmail.com https://bugs.freedesktop.org/show_bug.cgi?id=88898 We must be careful not to leave PR_SET_KEEPCAPS on. We could use the setresuid() call to drop capabilities, but the rules when capabilities are dropped are fairly complex, since a transition to non-zero uid must happen. Let's instead keep the capabilities during setresuid(), and drop them later. --- src/shared/capability.c | 32 ++++++++++++++++---------------- 1 file changed, 16 insertions(+), 16 deletions(-) (limited to 'src') diff --git a/src/shared/capability.c b/src/shared/capability.c index b39e8e2359..dcf7ce1a69 100644 --- a/src/shared/capability.c +++ b/src/shared/capability.c @@ -230,7 +230,6 @@ int capability_bounding_set_drop_usermode(uint64_t drop) { } int drop_privileges(uid_t uid, gid_t gid, uint64_t keep_capabilities) { - cap_value_t bits[sizeof(keep_capabilities)*8]; _cleanup_cap_free_ cap_t d = NULL; unsigned i, j = 0; int r; @@ -248,8 +247,8 @@ int drop_privileges(uid_t uid, gid_t gid, uint64_t keep_capabilities) { if (setgroups(0, NULL) < 0) return log_error_errno(errno, "Failed to drop auxiliary groups list: %m"); - /* Ensure we keep the permitted caps across the setresuid(), if we need them */ - if (prctl(PR_SET_KEEPCAPS, keep_capabilities != 0) < 0) + /* Ensure we keep the permitted caps across the setresuid() */ + if (prctl(PR_SET_KEEPCAPS, 1) < 0) return log_error_errno(errno, "Failed to enable keep capabilities flag: %m"); r = setresuid(uid, uid, uid); @@ -264,26 +263,27 @@ int drop_privileges(uid_t uid, gid_t gid, uint64_t keep_capabilities) { if (r < 0) return log_error_errno(r, "Failed to drop capabilities: %m"); - if (keep_capabilities == 0) /* All is gone, we can exit early */ - return 0; - /* Now upgrade the permitted caps we still kept to effective caps */ d = cap_init(); if (!d) return log_oom(); - for (i = 0; i < sizeof(keep_capabilities)*8; i++) - if (keep_capabilities & (1ULL << i)) - bits[j++] = i; + if (keep_capabilities) { + cap_value_t bits[sizeof(keep_capabilities)*8]; - if (cap_set_flag(d, CAP_EFFECTIVE, j, bits, CAP_SET) < 0 || - cap_set_flag(d, CAP_PERMITTED, j, bits, CAP_SET) < 0) { - log_error_errno(errno, "Failed to enable capabilities bits: %m"); - return -errno; - } + for (i = 0; i < sizeof(keep_capabilities)*8; i++) + if (keep_capabilities & (1ULL << i)) + bits[j++] = i; - if (cap_set_proc(d) < 0) - return log_error_errno(errno, "Failed to increase capabilities: %m"); + if (cap_set_flag(d, CAP_EFFECTIVE, j, bits, CAP_SET) < 0 || + cap_set_flag(d, CAP_PERMITTED, j, bits, CAP_SET) < 0) { + log_error_errno(errno, "Failed to enable capabilities bits: %m"); + return -errno; + } + + if (cap_set_proc(d) < 0) + return log_error_errno(errno, "Failed to increase capabilities: %m"); + } return 0; } -- cgit v1.2.3-54-g00ecf