update seccomp rules #818

dougsland · 2025-04-23T21:50:21Z

The current seccomp changes completely disallow calling sched_setscheduler, but we can safely allow calling it with policy==SCHED_OTHER/BATCH/IDLE, as really the only problem is the various real-time classes.

The profile argument is the second (id 1) and the values for the classes are OTHER=0, BATCH==3, IDLE==5

Resolves: #702

Summary by Sourcery

Bug Fixes:

Modify seccomp rules to permit sched_setscheduler calls with non-real-time scheduling policies

sourcery-ai · 2025-04-23T21:50:26Z

Reviewer's Guide by Sourcery

This pull request modifies the seccomp rules to allow the sched_setscheduler syscall with non-real-time scheduling policies (SCHED_OTHER, SCHED_BATCH, and SCHED_IDLE). This addresses issue #702 by permitting safe usage of sched_setscheduler while preventing the use of real-time scheduling policies that could cause problems.

No diagrams generated as the changes look simple and do not need a visual representation.

File-Level Changes

Change	Details	Files
Updated seccomp rules to allow `sched_setscheduler` with specific scheduling policies.	Allowed `sched_setscheduler` syscall when the policy is `SCHED_OTHER`, `SCHED_BATCH`, or `SCHED_IDLE`. Restricted `sched_setscheduler` syscall for real-time scheduling policies to prevent potential issues.	`create-seccomp-rules`

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sourcery-ai

Hey @dougsland - I've reviewed your changes - here's some feedback:

Overall Comments:

Consider adding a comment in the code explaining why these specific SCHED policies are allowed.

Here's what I looked at during the review

🟢 General issues: all looks good
🟢 Security: all looks good
🟢 Testing: all looks good
🟢 Complexity: all looks good
🟢 Documentation: all looks good

Sourcery is free for open source - if you like our reviews please consider sharing them ✨

_{Help me be more useful! Please click 👍 or 👎 on each comment and I'll use the feedback to improve your reviews.}

dougsland · 2025-04-23T21:51:15Z

Output now:

        {
                        "names": [
                                "sched_setscheduler"
                        ],
                        "action": "SCMP_ACT_ERRNO",
                        "args": [
                                {
                                        "index": 1,
                                        "value": 0,
                                        "valueTwo": 0,
                                        "op": "SCMP_CMP_NE"
                                },
                                {
                                        "index": 1,
                                        "value": 3,
                                        "valueTwo": 0,
                                        "op": "SCMP_CMP_NE"
                                },
                                {
                                        "index": 1,
                                        "value": 5,
                                        "valueTwo": 0,
                                        "op": "SCMP_CMP_NE"
                                }
                        ],
                        "errnoRet": 1,
                        "errno": "EPERM"
                },
                {
                        "names": [
                                "sched_setattr"
                        ],
                        "action": "SCMP_ACT_ERRNO",
                        "args": [],
                        "errnoRet": 1,
                        "errno": "EPERM"
                }

The current seccomp changes completely disallow calling sched_setscheduler, but we can safely allow calling it with policy==SCHED_OTHER/BATCH/IDLE, as really the only problem is the various real-time classes. The profile argument is the second (id 1) and the values for the classes are OTHER=0, BATCH==3, IDLE==5 Resolves: #702 Signed-off-by: Douglas Schilling Landgraf <[email protected]>

rhatdan · 2025-04-24T10:23:30Z

@giuseppe PTAL

giuseppe · 2025-04-24T10:27:08Z

where is the ALLOW rule added?

rhatdan · 2025-04-24T11:08:19Z

This is always something we should have added to podman
podman run --security-opt seccomp:+sched_setscheduler,foobar ...

Then add those access to allowed seccomp filters.

Similarly

podman run --security-opt seccomp:-ioclt,mkdir ...

alexlarsson · 2025-04-25T12:08:17Z

Looks good to me.

dougsland · 2025-05-01T21:58:42Z

Am I doing something wrong @alexlarsson?

#define _GNU_SOURCE
#include <sched.h>
#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <unistd.h>

void test_policy(int policy, const char *name) {
    struct sched_param param;
    param.sched_priority = 0; // default priority

    int result = sched_setscheduler(0, policy, &param);
    if (result == -1) {
        printf("sched_setscheduler(%s) failed: errno=%d (%s)\n", name, errno, strerror(errno));
    } else {
        printf("sched_setscheduler(%s) succeeded.\n", name);
    }
}

int main() {
    printf("Testing sched_setscheduler syscall with various policies:\n");

    test_policy(SCHED_OTHER, "SCHED_OTHER");
    test_policy(SCHED_BATCH, "SCHED_BATCH");
    test_policy(SCHED_IDLE, "SCHED_IDLE");
    test_policy(SCHED_FIFO, "SCHED_FIFO");
    test_policy(SCHED_RR, "SCHED_RR");

    return 0;
}

podman restart qm
cp binary /usr/lib/qm/rootfs/root/
podman exec -it qm bash
# ./binary
# Testing sched_setscheduler syscall with various policies:
sched_setscheduler(SCHED_OTHER) failed: errno=1 (Operation not permitted)
sched_setscheduler(SCHED_BATCH) failed: errno=1 (Operation not permitted)
sched_setscheduler(SCHED_IDLE) failed: errno=1 (Operation not permitted)
sched_setscheduler(SCHED_FIFO) failed: errno=1 (Operation not permitted)
sched_setscheduler(SCHED_RR) failed: errno=1 (Operation not permitted)

My seccomp:

    {
                        "names": [
                                "sched_setscheduler"
                        ],
                        "action": "SCMP_ACT_ERRNO",
                        "args": [
                                {
                                        "index": 1,
                                        "value": 0,
                                        "valueTwo": 0,
                                        "op": "SCMP_CMP_NE"
                                },
                                {
                                        "index": 1,
                                        "value": 3,
                                        "valueTwo": 0,
                                        "op": "SCMP_CMP_NE"
                                },
                                {
                                        "index": 1,
                                        "value": 5,
                                        "valueTwo": 0,
                                        "op": "SCMP_CMP_NE"
                                }
                        ],
                        "errnoRet": 1,
                        "errno": "EPERM"
                },
                {
                        "names": [
                                "sched_setattr"
                        ],
                        "action": "SCMP_ACT_ERRNO",
                        "args": [],
                        "errnoRet": 1,
                        "errno": "EPERM"
                }

dougsland · 2025-05-02T15:11:16Z

Sounds weird to me but this make it work as Function not implemented for SCHED_FIFO and SCHED_RR shows Operation not permitted.

                {
                  "names": ["sched_setscheduler"],
                  "action": "SCMP_ACT_ALLOW",
                  "args": [
                    { "index": 1, "value": 1, "op": "SCMP_CMP_NE" }
                  ],
                    "comment": "",
                    "includes": {
                    },
                    "excludes": {}
                },
                {
                  "names": ["sched_setscheduler"],
                  "action": "SCMP_ACT_ERRNO",
                  "args": [
                    { "index": 1, "value": 2, "op": "SCMP_CMP_EQ" }
                  ],
                  "errnoRet": 1
                },
                {
                  "names": ["sched_setattr"],
                  "action": "SCMP_ACT_ERRNO",
                  "errnoRet": 1
                }

bash-5.2# ./binary
Testing sched_setscheduler syscall with various policies:
sched_setscheduler(SCHED_OTHER) succeeded.
sched_setscheduler(SCHED_BATCH) succeeded.
sched_setscheduler(SCHED_IDLE) succeeded.
sched_setscheduler(SCHED_FIFO) failed: errno=38 (Function not implemented)
sched_setscheduler(SCHED_RR) failed: errno=1 (Operation not permitted)

Testing sched_setattr syscall:
sched_setattr(SCHED_RR) failed: errno=1 (Operation not permitted)

dougsland · 2025-05-02T15:19:16Z

On the other side, a simple rule like below works well (
please note: ("defaultAction": "SCMP_ACT_ALLOW")

bash-5.2# ./binary
Testing sched_setscheduler syscall with various policies:
sched_setscheduler(SCHED_OTHER) succeeded.
sched_setscheduler(SCHED_BATCH) succeeded.
sched_setscheduler(SCHED_IDLE) succeeded.
sched_setscheduler(SCHED_FIFO) failed: errno=1 (Operation not permitted)
sched_setscheduler(SCHED_RR) failed: errno=1 (Operation not permitted)

Testing sched_setattr syscall:
sched_setattr(SCHED_RR) failed: errno=1 (Operation not permitted)

{
  "defaultAction": "SCMP_ACT_ALLOW",
  "syscalls": [
    {
      "names": ["sched_setscheduler"],
      "action": "SCMP_ACT_ERRNO",
      "args": [
        { "index": 1, "value": 1, "op": "SCMP_CMP_EQ" }
      ],
      "errnoRet": 1
    },
    {
      "names": ["sched_setscheduler"],
      "action": "SCMP_ACT_ERRNO",
      "args": [
        { "index": 1, "value": 2, "op": "SCMP_CMP_EQ" }
      ],
      "errnoRet": 1
    },
    {
      "names": ["sched_setattr"],
      "action": "SCMP_ACT_ERRNO",
      "errnoRet": 1
    }
  ]
}

giuseppe · 2025-05-05T08:35:52Z

{
"names": [
"sched_setscheduler"
],
"action": "SCMP_ACT_ERRNO",
"args": [
{
"index": 1,
"value": 0,
"valueTwo": 0,
"op": "SCMP_CMP_NE"
},
{
"index": 1,
"value": 3,
"valueTwo": 0,
"op": "SCMP_CMP_NE"
},
{
"index": 1,
"value": 5,
"valueTwo": 0,
"op": "SCMP_CMP_NE"
}
],
"errnoRet": 1,
"errno": "EPERM"
},

have you tried adding 3 new rules ($arg1 == 0, $arg1 == 3, $arg1 == 5) each with action SCMP_ACT_ALLOW?

dougsland · 2025-05-06T23:56:09Z

{
"names": [
"sched_setscheduler"
],
"action": "SCMP_ACT_ERRNO",
"args": [
{
"index": 1,
"value": 0,
"valueTwo": 0,
"op": "SCMP_CMP_NE"
},
{
"index": 1,
"value": 3,
"valueTwo": 0,
"op": "SCMP_CMP_NE"
},
{
"index": 1,
"value": 5,
"valueTwo": 0,
"op": "SCMP_CMP_NE"
}
],
"errnoRet": 1,
"errno": "EPERM"
},

have you tried adding 3 new rules ($arg1 == 0, $arg1 == 3, $arg1 == 5) each with action SCMP_ACT_ALLOW?

Yes, with 3 allow. SCHED_FIFO SCHED_RR still succeeded

   {
           "names": ["sched_setscheduler"],
           "action": "SCMP_ACT_ALLOW",
           "args": [
               {
                   "index": 1,
                   "value": 0,
                   "valueTwo": 0,
                   "op": "SCMP_CMP_EQ"
               }
           ],
           "comment": "",
           "includes": {},
           "excludes": {}
       },
                {
           "names": ["sched_setscheduler"],
           "action": "SCMP_ACT_ALLOW",
           "args": [
               {
                   "index": 3,
                   "value": 0,
                   "valueTwo": 0,
                   "op": "SCMP_CMP_EQ"
               }
           ],
           "comment": "",
           "includes": {},
           "excludes": {}
       },
                {
           "names": ["sched_setscheduler"],
           "action": "SCMP_ACT_ALLOW",
           "args": [
               {
                   "index": 5,
                   "value": 0,
                   "valueTwo": 0,
                   "op": "SCMP_CMP_EQ"
               }
           ],
           "comment": "",
           "includes": {},
           "excludes": {}
       }

# ./binary
Testing sched_setscheduler syscall with various policies:
sched_setscheduler(SCHED_OTHER) succeeded.
sched_setscheduler(SCHED_BATCH) succeeded.
sched_setscheduler(SCHED_IDLE) succeeded.
sched_setscheduler(SCHED_FIFO) succeeded.
sched_setscheduler(SCHED_RR) succeeded.

dougsland requested review from rhatdan, Yarboa, nsednev, aesteve-rh, pengshanyu and kleinffm as code owners April 23, 2025 21:50

sourcery-ai bot approved these changes Apr 23, 2025

View reviewed changes

dougsland force-pushed the seccomp-perm branch from bc566b7 to 6cacfc6 Compare April 23, 2025 21:52

dougsland self-assigned this Apr 23, 2025

dougsland added the jira label Apr 23, 2025

Merge branch 'main' into seccomp-perm

6a7bf35

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update seccomp rules #818

update seccomp rules #818

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update seccomp rules #818

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update seccomp rules #818

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