diff options
author | Zbigniew Jędrzejewski-Szmek <zbyszek@in.waw.pl> | 2015-02-01 14:33:10 -0500 |
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committer | Zbigniew Jędrzejewski-Szmek <zbyszek@in.waw.pl> | 2015-02-01 17:22:32 -0500 |
commit | 51ddf61540976fc7b09ce5ace707b27f3acc3871 (patch) | |
tree | a9d404cb974572c5e52554c09186993d4d56719b | |
parent | 615938651d3a4fd9253b08da00db22d451a8cef8 (diff) |
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.
-rw-r--r-- | src/shared/capability.c | 32 |
1 files changed, 16 insertions, 16 deletions
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; } |