linux-kernel - [17/17] execve: make responsive to SIGKILL with large arguments

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Message-Id: <20101022184034.003754079@clark.site>
Date:	Fri, 22 Oct 2010 11:39:42 -0700
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Roland McGrath <roland@...hat.com>,
	Chuck Ebbert <cebbert@...hat.com>
Subject: [17/17] execve: make responsive to SIGKILL with large arguments

2.6.27-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Roland McGrath <roland@...hat.com>

commit 9aea5a65aa7a1af9a4236dfaeb0088f1624f9919 upstream.

An execve with a very large total of argument/environment strings
can take a really long time in the execve system call.  It runs
uninterruptibly to count and copy all the strings.  This change
makes it abort the exec quickly if sent a SIGKILL.

Note that this is the conservative change, to interrupt only for
SIGKILL, by using fatal_signal_pending().  It would be perfectly
correct semantics to let any signal interrupt the string-copying in
execve, i.e. use signal_pending() instead of fatal_signal_pending().
We'll save that change for later, since it could have user-visible
consequences, such as having a timer set too quickly make it so that
an execve can never complete, though it always happened to work before.

Signed-off-by: Roland McGrath <roland@...hat.com>
Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc: Chuck Ebbert <cebbert@...hat.com>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>

---
 fs/exec.c |    7 +++++++
 1 file changed, 7 insertions(+)

--- a/fs/exec.c
+++ b/fs/exec.c
@@ -393,6 +393,9 @@ static int count(char __user * __user *
 			argv++;
 			if(++i > max)
 				return -E2BIG;
+
+			if (fatal_signal_pending(current))
+				return -ERESTARTNOHAND;
 			cond_resched();
 		}
 	}
@@ -436,6 +439,10 @@ static int copy_strings(int argc, char _
 		while (len > 0) {
 			int offset, bytes_to_copy;

+			if (fatal_signal_pending(current)) {
+				ret = -ERESTARTNOHAND;
+				goto out;
+			}
 			cond_resched();

 			offset = pos % PAGE_SIZE;

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