linux-kernel - [patch] proc.5: tell how to parse /proc/*/stat correctly

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Message-ID: <Y6SJDbKBk471KE4k@p183>
Date:   Thu, 22 Dec 2022 19:42:53 +0300
From:   Alexey Dobriyan <adobriyan@...il.com>
To:     Alejandro Colomar <alx.manpages@...il.com>,
        Michael Kerrisk <mtk.manpages@...il.com>
Cc:     linux-kernel@...r.kernel.org, linux-man@...r.kernel.org,
        oss-security@...ts.openwall.com
Subject: [patch] proc.5: tell how to parse /proc/*/stat correctly

/proc/*/stat can't be parsed with split() or split(" ") or split(' ')
or sscanf("%d (%s) ...") or equivalents because "comm" can contain
whitespace and parenthesis and is not escaped by the kernel.

BTW escaping would not help with naive split() anyway.

Mention strrchr(')') so people can at least stop adding new bugs.

Signed-off-by: Alexey Dobriyan <adobriyan@...il.com>
---

 man5/proc.5 |    5 +++++
 1 file changed, 5 insertions(+)

--- a/man5/proc.5
+++ b/man5/proc.5
@@ -2092,6 +2092,11 @@ Strings longer than
 .B TASK_COMM_LEN
 (16) characters (including the terminating null byte) are silently truncated.
 This is visible whether or not the executable is swapped out.
+
+Note that \fIcomm\fP can contain space and closing parenthesis characters. 
+Parsing /proc/${pid}/stat with split() or equivalent, or scanf(3) isn't
+reliable. The correct way is to locate closing parenthesis with strrchr(')')
+from the end of the buffer and parse integers from there.
 .TP
 (3) \fIstate\fP \ %c
 One of the following characters, indicating process state: