execve: make responsive to SIGKILL with large arguments

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@redhat.com>
Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>

diff --git a/fs/exec.c b/fs/exec.c
index b187ab03133f1212f524c419c8dfb325245e57ce..afd9977fca2a2f54bbbd8a9a1b47ed2fb6aa699a 100644 (file)
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -376,6 +376,9 @@ static int count(char __user * __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, char __user * __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;