[PATCH 3/3] execve: make responsive to SIGKILL with large arguments

[Roland McGrath <roland@redhat.com>]

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@redhat.com>
---
 fs/exec.c |    7 +++++++
 1 files changed, 7 insertions(+), 0 deletions(-)

diff --git a/fs/exec.c b/fs/exec.c
index 6f2d777..828dd24 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -376,6 +376,9 @@ static int count(const char __user * const __user * argv, int max)
 			argv++;
 			if (i++ >= max)
 				return -E2BIG;
+
+			if (fatal_signal_pending(current))
+				return -ERESTARTNOHAND;
 			cond_resched();
 		}
 	}
@@ -419,6 +422,10 @@ static int copy_strings(int argc, const char __user *const __user *argv,
 		while (len > 0) {
 			int offset, bytes_to_copy;
 
+			if (fatal_signal_pending(current)) {
+				ret = -ERESTARTNOHAND;
+				goto out;
+			}
 			cond_resched();
 
 			offset = pos % PAGE_SIZE;