ptrace.2: Further fixes after review from Jann Horn

Reported-by: Jann Horn <jann@thejh.net>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

diff --git a/man2/ptrace.2 b/man2/ptrace.2
index 507540ba8cf801446b794cd8f82626800934acfd..82c04ad8acaf90742a241e589ef24a5a3d6c7249 100644 (file)
--- a/man2/ptrace.2
+++ b/man2/ptrace.2
@@ -2183,12 +2183,20 @@ thread group, access is always allowed.
 .IP 2.
 If the access mode specifies
 .BR PTRACE_MODE_FSCREDS ,
-then for the check in the next step,
-employ the caller's filesystem user ID and group ID (see
-.BR credentials (7));
-otherwise (the access mode specifies
+then, for the check in the next step,
+employ the caller's filesystem UID and GID.
+(As noted in
+.BR credentials (7),
+the filesystem UID and GID almost always have the same values
+as the corresponding effective IDs.)
+
+Otherwise, the access mode specifies
 .BR PTRACE_MODE_REALCREDS ,
-so) use the caller's real user ID and group ID.
+so use the caller's real UID and GID for the checks in the next step.
+(Most APIs that check the caller's UID and GID use the effective IDs.
+For historical reasons, the
+.BR PTRACE_MODE_REALCREDS
+check uses the real IDs instead.)
 .IP 3.
 Deny access if
 .I neither