net: Fix recursive descent in __scm_destroy().

__scm_destroy() walks the list of file descriptors in the scm_fp_list
pointed to by the scm_cookie argument.

Those, in turn, can close sockets and invoke __scm_destroy() again.

There is nothing which limits how deeply this can occur.

The idea for how to fix this is from Linus.  Basically, we do all of
the fput()s at the top level by collecting all of the scm_fp_list
objects hit by an fput().  Inside of the initial __scm_destroy() we
keep running the list until it is empty.

Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/linux/sched.h b/include/linux/sched.h
index b483f39a7112073e17c6ce8edc2fa0b17c9b61e1..295b7c756ca6107aee29ee4c12e3eb2f486c9f7e 100644 (file)
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1349,6 +1349,8 @@ struct task_struct {
         */
        unsigned long timer_slack_ns;
        unsigned long default_timer_slack_ns;
+
+       struct list_head        *scm_work_list;
 };
 
 /*

diff --git a/include/net/scm.h b/include/net/scm.h
index 06df126103cab8224d6cf7ae64c7f00e75f06e12..33e9986beb86dd95d6f3f962ca8a89281c874a9d 100644 (file)
--- a/include/net/scm.h
+++ b/include/net/scm.h
@@ -14,8 +14,9 @@
 
 struct scm_fp_list
 {
-       int             count;
-       struct file     *fp[SCM_MAX_FD];
+       struct list_head        list;
+       int                     count;
+       struct file             *fp[SCM_MAX_FD];
 };
 
 struct scm_cookie

diff --git a/net/core/scm.c b/net/core/scm.c
index 10f5c65f6a470cc914de500b43d63990e89db1b6..ab242cc1accaae7673b76784aa5838a76d9b10c4 100644 (file)
--- a/net/core/scm.c
+++ b/net/core/scm.c
@@ -75,6 +75,7 @@ static int scm_fp_copy(struct cmsghdr *cmsg, struct scm_fp_list **fplp)
                if (!fpl)
                        return -ENOMEM;
                *fplp = fpl;
+               INIT_LIST_HEAD(&fpl->list);
                fpl->count = 0;
        }
        fpp = &fpl->fp[fpl->count];
@@ -106,9 +107,25 @@ void __scm_destroy(struct scm_cookie *scm)
 
        if (fpl) {
                scm->fp = NULL;
-               for (i=fpl->count-1; i>=0; i--)
-                       fput(fpl->fp[i]);
-               kfree(fpl);
+               if (current->scm_work_list) {
+                       list_add_tail(&fpl->list, current->scm_work_list);
+               } else {
+                       LIST_HEAD(work_list);
+
+                       current->scm_work_list = &work_list;
+
+                       list_add(&fpl->list, &work_list);
+                       while (!list_empty(&work_list)) {
+                               fpl = list_first_entry(&work_list, struct scm_fp_list, list);
+
+                               list_del(&fpl->list);
+                               for (i=fpl->count-1; i>=0; i--)
+                                       fput(fpl->fp[i]);
+                               kfree(fpl);
+                       }
+
+                       current->scm_work_list = NULL;
+               }
        }
 }
 
@@ -284,6 +301,7 @@ struct scm_fp_list *scm_fp_dup(struct scm_fp_list *fpl)
 
        new_fpl = kmalloc(sizeof(*fpl), GFP_KERNEL);
        if (new_fpl) {
+               INIT_LIST_HEAD(&new_fpl->list);
                for (i=fpl->count-1; i>=0; i--)
                        get_file(fpl->fp[i]);
                memcpy(new_fpl, fpl, sizeof(*fpl));