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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>
This commit is contained in:
David S. Miller 2008-11-06 15:45:32 -08:00
parent 518a09ef11
commit 3b53fbf431
3 changed files with 26 additions and 5 deletions
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2
include/linux/sched.h
View File

@ -1349,6 +1349,8 @@ struct task_struct {
*/
unsigned long timer_slack_ns;
unsigned long default_timer_slack_ns;
struct list_head *scm_work_list;
};
/*

5
include/net/scm.h
View File

@ -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

24
net/core/scm.c
View File

@ -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));