sys/linux/test: improve landlock_ptrace

When running syz-manager with -mode run-tests --tests landlock_ptrace -debug
we get this result:

  executing program
  ### start
  ### call=0 errno=0
  ### call=1 errno=0
  ### call=2 errno=0
  ### call=3 errno=0
  ### call=4 errno=3
  ### call=5 errno=0
  ### call=6 errno=0
  ### call=7 errno=0
  ### call=8 errno=1
  ### call=9 errno=0
  ### call=10 errno=0
  ### call=11 errno=3
  ### call=12 errno=0
  ### call=13 errno=0
  ### call=14 errno=1
  ### call=15 errno=3
  ### call=16 errno=1
  ### call=17 errno=0
  ### call=18 errno=3
  executing program
  ### start
  ### call=0 errno=0
  ### call=1 errno=0
  ### call=2 errno=0
  ### call=3 errno=0
  ### call=4 errno=0
  ### call=5 errno=0
  ### call=6 errno=0
  ### call=7 errno=0
  ### call=8 errno=1
  ### call=9 errno=3
  ### call=10 errno=0
  ### call=11 errno=3
  ### call=12 errno=0
  ### call=13 errno=0
  ### call=14 errno=1
  ### call=15 errno=3
  ### call=16 errno=1
  ### call=17 errno=0
  ### call=18 errno=3
  executing program
  ### start
  ### call=0 errno=0
  ### call=1 errno=0
  ### call=2 errno=0
  ### call=3 errno=0
  ### call=4 errno=3
  ### call=5 errno=0
  ### call=6 errno=0
  ### call=7 errno=0
  ### call=8 errno=1
  ### call=9 errno=0
  ### call=10 errno=0
  ### call=11 errno=3
  ### call=12 errno=0
  ### call=13 errno=0
  ### call=14 errno=1
  ### call=15 errno=3
  ### call=16 errno=1
  ### call=17 errno=0
  ### call=18 errno=3

Because this test spawns two threads, the ptrace(2) returned code may be
different according to the calling thread.

Set the common EPERM errnos for all three threads (EINTR is unknown to
syzkaller).  The other returned codes cannot be fixed because we cannot
have a set of valid errno for the same call.

Signed-off-by: Mickaël Salaün <mic@linux.microsoft.com>

Author: l0kod

sys/linux/test/landlock_ptrace

@@ -1,5 +1,8 @@
 # Creates independent Landlock hierarchies and try different tracer/tracee
 # schemas (without scheduling control).
+#
+# In this test, some ptrace(2) calls return different code according to the
+# calling thread.
 
 capset(&AUTO={0x20080522, 0x0}, &AUTO={0x0, 0x0, 0x0, 0x0, 0x0, 0x0})
 prctl$PR_SET_NO_NEW_PRIVS(0x26, 0x1)
@@ -16,7 +19,7 @@ landlock_restrict_self(r1, 0x0)
 
 r2 = syz_clone(0x11, 0x0, 0x0, 0x0, 0x0, 0x0)
 
-ptrace(0x10, r0)
+ptrace(0x10, r0) # EPERM
 ptrace(0x11, r0)
 
 ptrace(0x10, r2)
@@ -25,10 +28,10 @@ ptrace(0x11, r2)
 r3 = landlock_create_ruleset(&AUTO={0x100, 0x0, 0x0}, AUTO, 0x0)
 landlock_restrict_self(r3, 0x0)
 
-ptrace(0x10, r0)
+ptrace(0x10, r0) # EPERM
 ptrace(0x11, r0)
 
-ptrace(0x10, r2)
+ptrace(0x10, r2) # EPERM
 ptrace(0x11, r2)
 
 # For now, PTRACE_TRACEME is transformed to -1, which returns an error: