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fix(ebpf): treat sched_process_exit corner case #4557

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merged 1 commit into from
Jan 29, 2025
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fix(ebpf): treat sched_process_exit corner case #4557

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18 changes: 18 additions & 0 deletions pkg/ebpf/c/tracee.bpf.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1521,6 +1521,24 @@ int tracepoint__sched__sched_process_exit(struct bpf_raw_tracepoint_args *ctx)
if (!init_program_data(&p, ctx, SCHED_PROCESS_EXIT))
return 0;

// The syscall number cannot be trusted in the following cases:
//
// 1. If the task was terminated due to a signal (PF_SIGNALED is set), the syscall
// context may be inconsistent.
//
// 2. If the task was not signaled:
// - A kernel thread (PF_KTHREAD is set) is not expected to have a valid syscall context, so
// the function init_program_data has already set its syscall number as NO_SYSCALL (-1).
// - If PF_KTHREAD is not set but the syscall value is negative, it may be due to
// an invalid or clobbered context.
//
// In any of these cases, we explicitly mark the syscall number as NO_SYSCALL (-1) to avoid
// misinterpretation.
int task_flags = get_task_flags(p.event->task);
if ((task_flags & PF_SIGNALED) ||
(!(task_flags & PF_KTHREAD) && (p.event->context.syscall < 0)))
p.event->context.syscall = NO_SYSCALL;

// evaluate matched_policies before removing this pid from the maps
evaluate_scope_filters(&p);

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3 changes: 2 additions & 1 deletion pkg/ebpf/c/vmlinux_missing.h
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Expand Up @@ -48,7 +48,8 @@

#define ICMPV6_ECHO_REQUEST 128

#define PF_KTHREAD 0x00200000 /* I am a kernel thread */
#define PF_SIGNALED 0x00000400 /* Killed by a signal */
#define PF_KTHREAD 0x00200000 /* I am a kernel thread */

#define TASK_COMM_LEN 16

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3 changes: 1 addition & 2 deletions pkg/ebpf/events_pipeline.go
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Expand Up @@ -221,10 +221,9 @@ func (t *Tracee) decodeEvents(ctx context.Context, sourceChan chan []byte) (<-ch
id := events.ID(eCtx.Syscall)
syscallDef := events.Core.GetDefinitionByID(id)
if syscallDef.NotValid() {
// This should never fail, as the translation used in eBPF relies on the same event definitions
commStr := string(eCtx.Comm[:bytes.IndexByte(eCtx.Comm[:], 0)])
utsNameStr := string(eCtx.UtsName[:bytes.IndexByte(eCtx.UtsName[:], 0)])
logger.Errorw(
logger.Debugw(
fmt.Sprintf("Event %s with an invalid syscall id %d", evtName, id),
"Comm", commStr,
"UtsName", utsNameStr,
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