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From 6135d6239a40edb260dde80e5662d3e062dde0bd Mon Sep 17 00:00:00 2001
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From: Nick Rosbrook <nick.rosbrook@canonical.com>
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Date: Tue, 22 Nov 2022 10:33:55 -0500
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Subject: [PATCH] oomd: always allow root-owned cgroups to set
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 ManagedOOMPreference
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Commit 652a4efb66a ("oomd: loosen the restriction on ManagedOOMPreference")
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made the change to allow ManagedOOMPreference on a cgroup candidate when
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the monitored cgroup and cgroup candidate are owned by the same user.
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The commit assumed that this check was sufficient to continue allowing
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ManagedOOMPreference on all cgroups owned by root. However, it caused a
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regression for unprivileged LXD containers where e.g. /sys/fs/cgroup is
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owned by nobody (uid=65534).
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Fix this by explicitly allowing the ManagedOOMPreference if uid == 0 in
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oomd_fetch_cgroup_oom_preference().
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(cherry picked from commit 89186093485b52ca957d17842fc1f7c87958454a)
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Related: #2138081
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---
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 src/oom/oomd-util.c | 2 +-
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 1 file changed, 1 insertion(+), 1 deletion(-)
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diff --git a/src/oom/oomd-util.c b/src/oom/oomd-util.c
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index 1fc81d1843..70a1dc941e 100644
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--- a/src/oom/oomd-util.c
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+++ b/src/oom/oomd-util.c
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@@ -164,7 +164,7 @@ int oomd_fetch_cgroup_oom_preference(OomdCGroupContext *ctx, const char *prefix)
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         if (r < 0)
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                 return log_debug_errno(r, "Failed to get owner/group from %s: %m", ctx->path);
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-        if (uid == prefix_uid) {
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+        if (uid == prefix_uid || uid == 0) {
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                 /* Ignore most errors when reading the xattr since it is usually unset and cgroup xattrs are only used
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                  * as an optional feature of systemd-oomd (and the system might not even support them). */
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                 r = cg_get_xattr_bool(SYSTEMD_CGROUP_CONTROLLER, ctx->path, "user.oomd_avoid");