git: d3f0d2c0eef6 - stable/13 - linux: Add additional ptracestop only if the debugger is Linux

The branch stable/13 has been updated by trasz:

URL: https://cgit.FreeBSD.org/src/commit/?id=d3f0d2c0eef6ef2092cd66db02aace57eb3c6a4d

commit d3f0d2c0eef6ef2092cd66db02aace57eb3c6a4d
Author:     Edward Tomasz Napierala <trasz@FreeBSD.org>
AuthorDate: 2021-10-30 08:53:55 +0000
Commit:     Edward Tomasz Napierala <trasz@FreeBSD.org>
CommitDate: 2022-02-21 14:31:22 +0000

    linux: Add additional ptracestop only if the debugger is Linux
    
    In 6e66030c4c0, additional ptracestop was added in order
    to implement PTRACE_EVENT_EXEC.  Make it only apply to cases
    where the debugger is a Linux processes; native FreeBSD
    debuggers can trace Linux processes too, but they don't
    expect that additonal ptracestop.
    
    Fixes:          6e66030c4c0
    Reported By:    kib
    Reviewed By:    kib
    Sponsored By:   EPSRC
    Differential Revision:  https://reviews.freebsd.org/D32726
    
    (cherry picked from commit 8bbc0600cc21bbfdc3b8e67199eec4220952b7e3)
---
 sys/kern/subr_syscall.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/sys/kern/subr_syscall.c b/sys/kern/subr_syscall.c
index dee81ba0fa48..8507c5393c01 100644
--- a/sys/kern/subr_syscall.c
+++ b/sys/kern/subr_syscall.c
@@ -261,9 +261,15 @@ syscallret(struct thread *td)
 		 * the exec event now and then clear TDB_EXEC so that
 		 * the next stop is reported as a syscall exit by
 		 * linux_ptrace_status().
+		 *
+		 * We are accessing p->p_pptr without any additional
+		 * locks here: it cannot change while p is kept locked;
+		 * while the debugger could in theory change its ABI
+		 * while tracing another process, the outcome of such
+		 * a race wouln't be deterministic anyway.
 		 */
-		if ((td->td_dbgflags & TDB_EXEC) != 0 &&
-		    SV_PROC_ABI(td->td_proc) == SV_ABI_LINUX) {
+		if (traced && (td->td_dbgflags & TDB_EXEC) != 0 &&
+		    SV_PROC_ABI(p->p_pptr) == SV_ABI_LINUX) {
 			ptracestop(td, SIGTRAP, NULL);
 			td->td_dbgflags &= ~TDB_EXEC;
 		}