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Make buildah's handling of ulimits match podman #5590

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Make buildah's handling of ulimits match podman #5590

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a5a2655
Make buildah handling of ulimits match podman
chris-reeves Jun 14, 2024
1036cfd
Make limits tests have consistent wording
chris-reeves Jun 15, 2024
5241c92
Always try to set nofile limit
chris-reeves Jun 16, 2024
6646b57
Check return value of Setrlimit() to keep linter happy
chris-reeves Jun 17, 2024
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32 changes: 27 additions & 5 deletions run_linux.go
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Original file line number Diff line number Diff line change
Expand Up @@ -1003,28 +1003,50 @@ func addRlimits(ulimit []string, g *generate.Generator, defaultUlimits []string)
g.AddProcessRlimits("RLIMIT_"+strings.ToUpper(ul.Name), uint64(ul.Hard), uint64(ul.Soft))
}
if !nofileSet {
max := define.RLimitDefaultValue
// For nofile, podman first tries to set both the hard and soft limits for the current
// process to RLimitDefaultValue - this will be successful in most (but not all)
// non-rootless environments. If this fails (e.g. in a rootless environment) it will ensure
// that the soft limit for the current process is increased to match the hard limit (see
// cmd/podman/early_init_linux.go).
var rlimit unix.Rlimit
rlimit.Cur = define.RLimitDefaultValue
rlimit.Max = define.RLimitDefaultValue
err := unix.Setrlimit(unix.RLIMIT_NOFILE, &rlimit)
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If the limits are set higher than this on entry, are we lowering them for the calling process? I don't know that I want that as a side-effect.

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If the limits are currently greater than define.RLimitDefaultValue then yes, they will be lowered (but for the current buildah process, not for any calling process).

There are three reasons why I don't think this is an issue:

  • define.RLimitDefaultValue is 1048576, which matches the default kernel hard limit;
  • the purpose of Make buildah match podman for handling of ulimits #5275 (which this PR is a continuation of) was to match the behaviour of podman (and this is what podman does);
  • if a user does need a higher limit for some reason, they can simply set the --ulimit option.

if err != nil {
// We don't really care whether there's an error here, because if it fails we
// effectively handle setting soft to hard in the call to AddProcessRlimits() later on.
logrus.Debugf("Failed to set RLIMIT_NOFILE ulimit %q", err)
}

// Set both hard and soft limits to min(hard limit, RLimitDefaultValue) regardless of
// rootlessness.
max := define.RLimitDefaultValue
if err := unix.Getrlimit(unix.RLIMIT_NOFILE, &rlimit); err == nil {
if max < rlimit.Max || unshare.IsRootless() {
if rlimit.Max < max {
max = rlimit.Max
}
} else {
logrus.Warnf("Failed to return RLIMIT_NOFILE ulimit %q", err)
}
g.AddProcessRlimits("RLIMIT_NOFILE", max, max)
}
if !nprocSet {
if !nprocSet && unshare.IsRootless() {
// For nproc, podman only sets limits for rootless containers (handling hard and soft limits
// independently). As before, these are set to min(soft/hard limit, RLimitDefaultValue).
current := define.RLimitDefaultValue
max := define.RLimitDefaultValue
var rlimit unix.Rlimit
if err := unix.Getrlimit(unix.RLIMIT_NPROC, &rlimit); err == nil {
if max < rlimit.Max || unshare.IsRootless() {
if rlimit.Max < max {
max = rlimit.Max
}
if rlimit.Cur < current {
current = rlimit.Cur
}
} else {
logrus.Warnf("Failed to return RLIMIT_NPROC ulimit %q", err)
}
g.AddProcessRlimits("RLIMIT_NPROC", max, max)
g.AddProcessRlimits("RLIMIT_NPROC", max, current)
}

return nil
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10 changes: 7 additions & 3 deletions tests/run.bats
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Original file line number Diff line number Diff line change
Expand Up @@ -524,18 +524,22 @@ function configure_and_check_user() {

_prefetch alpine

run podman run --rm alpine sh -c "awk '/open files/{print \$4 \"/\" \$5}' /proc/self/limits"
podman_files=$output
# drop limits prior to tests - this tests the ability of non-rootless containers to increase
# file limits to match those of podman
ulimit -S -n 1024
ulimit -H -n 1024

run_buildah from --quiet --pull=false $WITH_POLICY_JSON alpine
cid=$output
run podman run --rm alpine sh -c "awk '/open files/{print \$4 \"/\" \$5}' /proc/self/limits"
podman_files=$output
run_buildah run $cid awk '/open files/{print $4 "/" $5}' /proc/self/limits
expect_output "${podman_files}" "limits: podman and buildah should agree on open files"

run podman run --rm alpine sh -c "awk '/processes/{print \$3 \"/\" \$4}' /proc/self/limits"
podman_processes=$output
run_buildah run $cid awk '/processes/{print $3 "/" $4}' /proc/self/limits
expect_output ${podman_processes} "processes should match podman"
expect_output "${podman_processes}" "limits: podman and buildah should agree on processes"
run_buildah rm $cid

run_buildah from --quiet --ulimit nofile=300:400 --pull=false $WITH_POLICY_JSON alpine
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