exec: copy-and-paste the fixes into compat_do_execve() paths

Note: this patch targets 2.6.37 and tries to be as simple as possible.
That is why it adds more copy-and-paste horror into fs/compat.c and
uglifies fs/exec.c, this will be cleanuped later.

compat_copy_strings() plays with bprm->vma/mm directly and thus has
two problems: it lacks the RLIMIT_STACK check and argv/envp memory
is not visible to oom killer.

Export acct_arg_size() and get_arg_page(), change compat_copy_strings()
to use get_arg_page(), change compat_do_execve() to do acct_arg_size(0)
as do_execve() does.

Add the fatal_signal_pending/cond_resched checks into compat_count() and
compat_copy_strings(), this matches the code in fs/exec.c and certainly
makes sense.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: stable@kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 23 insertions, 17 deletions

diff --git a/fs/compat.c b/fs/compat.c
index c580c322fa6b..eb1740ac8c0a 100644
--- a/fs/compat.c
+++ b/fs/compat.c
@@ -1350,6 +1350,10 @@ static int compat_count(compat_uptr_t __user *argv, int max)
                         argv++;
                         if (i++ >= max)
                                 return -E2BIG;
+
+                        if (fatal_signal_pending(current))
+                                return -ERESTARTNOHAND;
+                        cond_resched();
                 }
         }
         return i;
@@ -1391,6 +1395,12 @@ static int compat_copy_strings(int argc, compat_uptr_t __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;
                         if (offset == 0)
                                 offset = PAGE_SIZE;
@@ -1407,18 +1417,8 @@ static int compat_copy_strings(int argc, compat_uptr_t __user *argv,
                         if (!kmapped_page || kpos != (pos & PAGE_MASK)) {
                                 struct page *page;
 
-#ifdef CONFIG_STACK_GROWSUP
-                                ret = expand_stack_downwards(bprm->vma, pos);
-                                if (ret < 0) {
-                                        /* We've exceed the stack rlimit. */
-                                        ret = -E2BIG;
-                                        goto out;
-                                }
-#endif
-                                ret = get_user_pages(current, bprm->mm, pos,
-                                                     1, 1, 1, &page, NULL);
-                                if (ret <= 0) {
-                                        /* We've exceed the stack rlimit. */
+                                page = get_arg_page(bprm, pos, 1);
+                                if (!page) {
                                         ret = -E2BIG;
                                         goto out;
                                 }
@@ -1539,8 +1539,10 @@ int compat_do_execve(char * filename,
         return retval;
 
 out:
-        if (bprm->mm)
+        if (bprm->mm) {
+                acct_arg_size(bprm, 0);
                 mmput(bprm->mm);
+        }
 
 out_file:
         if (bprm->file) {
diff --git a/fs/exec.c b/fs/exec.c
index 4303b9035fe7..d68c378a3137 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -164,7 +164,7 @@ out:
 
 #ifdef CONFIG_MMU
 
-static void acct_arg_size(struct linux_binprm *bprm, unsigned long pages)
+void acct_arg_size(struct linux_binprm *bprm, unsigned long pages)
 {
         struct mm_struct *mm = current->mm;
         long diff = (long)(pages - bprm->vma_pages);
@@ -183,7 +183,7 @@ static void acct_arg_size(struct linux_binprm *bprm, unsigned long pages)
 #endif
 }
 
-static struct page *get_arg_page(struct linux_binprm *bprm, unsigned long pos,
+struct page *get_arg_page(struct linux_binprm *bprm, unsigned long pos,
                 int write)
 {
         struct page *page;
@@ -297,11 +297,11 @@ static bool valid_arg_len(struct linux_binprm *bprm, long len)
 
 #else
 
-static inline void acct_arg_size(struct linux_binprm *bprm, unsigned long pages)
+void acct_arg_size(struct linux_binprm *bprm, unsigned long pages)
 {
 }
 
-static struct page *get_arg_page(struct linux_binprm *bprm, unsigned long pos,
+struct page *get_arg_page(struct linux_binprm *bprm, unsigned long pos,
                 int write)
 {
         struct page *page;
diff --git a/include/linux/binfmts.h b/include/linux/binfmts.h
index 7c87796d20da..64a7114a9394 100644
--- a/include/linux/binfmts.h
+++ b/include/linux/binfmts.h
@@ -60,6 +60,10 @@ struct linux_binprm{
         unsigned long loader, exec;
 };
 
+extern void acct_arg_size(struct linux_binprm *bprm, unsigned long pages);
+extern struct page *get_arg_page(struct linux_binprm *bprm, unsigned long pos,
+                                        int write);
+
 #define BINPRM_FLAGS_ENFORCE_NONDUMP_BIT 0
 #define BINPRM_FLAGS_ENFORCE_NONDUMP (1 << BINPRM_FLAGS_ENFORCE_NONDUMP_BIT)