unix: correctly track in-flight fds in sending process user_struct

commit 415e3d3e90ce9e18727e8843ae343eda5a58fad6 upstream.

The commit referenced in the Fixes tag incorrectly accounted the number
of in-flight fds over a unix domain socket to the original opener
of the file-descriptor. This allows another process to arbitrary
deplete the original file-openers resource limit for the maximum of
open files. Instead the sending processes and its struct cred should
be credited.

To do so, we add a reference counted struct user_struct pointer to the
scm_fp_list and use it to account for the number of inflight unix fds.

Fixes: 712f4aad406bb1 ("unix: properly account for FDs passed over unix sockets")
Reported-by: David Herrmann <dh.herrmann@gmail.com>
Cc: David Herrmann <dh.herrmann@gmail.com>
Cc: Willy Tarreau <w@1wt.eu>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/include/net/af_unix.h b/include/net/af_unix.h
index f4842f7..a69bfee 100644 (file)
--- a/include/net/af_unix.h
+++ b/include/net/af_unix.h
@@ -6,8 +6,8 @@
 #include <linux/mutex.h>
 #include <net/sock.h>
 
-extern void unix_inflight(struct file *fp);
-extern void unix_notinflight(struct file *fp);
+extern void unix_inflight(struct user_struct *user, struct file *fp);
+extern void unix_notinflight(struct user_struct *user, struct file *fp);
 extern void unix_gc(void);
 extern void wait_for_unix_gc(void);
 extern struct sock *unix_get_socket(struct file *filp);

diff --git a/include/net/scm.h b/include/net/scm.h
index 5da0a7b..9822a68 100644 (file)
--- a/include/net/scm.h
+++ b/include/net/scm.h
@@ -16,6 +16,7 @@ struct scm_fp_list {
        struct list_head        list;
        short                   count;
        short                   max;
+       struct user_struct      *user;
        struct file             *fp[SCM_MAX_FD];
 };
 

diff --git a/net/core/scm.c b/net/core/scm.c
index 51b4d52..9adabed 100644 (file)
--- a/net/core/scm.c
+++ b/net/core/scm.c
@@ -80,6 +80,7 @@ static int scm_fp_copy(struct cmsghdr *cmsg, struct scm_fp_list **fplp)
                *fplp = fpl;
                fpl->count = 0;
                fpl->max = SCM_MAX_FD;
+               fpl->user = NULL;
        }
        fpp = &fpl->fp[fpl->count];
 
@@ -100,6 +101,10 @@ static int scm_fp_copy(struct cmsghdr *cmsg, struct scm_fp_list **fplp)
                *fpp++ = file;
                fpl->count++;
        }
+
+       if (!fpl->user)
+               fpl->user = get_uid(current_user());
+
        return num;
 }
 
@@ -124,6 +129,7 @@ void __scm_destroy(struct scm_cookie *scm)
                                list_del(&fpl->list);
                                for (i=fpl->count-1; i>=0; i--)
                                        fput(fpl->fp[i]);
+                               free_uid(fpl->user);
                                kfree(fpl);
                        }
 
@@ -342,6 +348,7 @@ struct scm_fp_list *scm_fp_dup(struct scm_fp_list *fpl)
                for (i = 0; i < fpl->count; i++)
                        get_file(fpl->fp[i]);
                new_fpl->max = new_fpl->count;
+               new_fpl->user = get_uid(fpl->user);
        }
        return new_fpl;
 }

diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 6798b3c..390e079 100644 (file)
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -1454,7 +1454,7 @@ static void unix_detach_fds(struct scm_cookie *scm, struct sk_buff *skb)
        UNIXCB(skb).fp = NULL;
 
        for (i = scm->fp->count-1; i >= 0; i--)
-               unix_notinflight(scm->fp->fp[i]);
+               unix_notinflight(scm->fp->user, scm->fp->fp[i]);
 }
 
 static void unix_destruct_scm(struct sk_buff *skb)
@@ -1520,7 +1520,7 @@ static int unix_attach_fds(struct scm_cookie *scm, struct sk_buff *skb)
                return -ENOMEM;
 
        for (i = scm->fp->count - 1; i >= 0; i--)
-               unix_inflight(scm->fp->fp[i]);
+               unix_inflight(scm->fp->user, scm->fp->fp[i]);
        return max_level;
 }
 

diff --git a/net/unix/garbage.c b/net/unix/garbage.c
index fd1a840..33a2126 100644 (file)
--- a/net/unix/garbage.c
+++ b/net/unix/garbage.c
@@ -122,7 +122,7 @@ struct sock *unix_get_socket(struct file *filp)
  *     descriptor if it is for an AF_UNIX socket.
  */
 
-void unix_inflight(struct file *fp)
+void unix_inflight(struct user_struct *user, struct file *fp)
 {
        struct sock *s = unix_get_socket(fp);
 
@@ -138,11 +138,11 @@ void unix_inflight(struct file *fp)
                }
                unix_tot_inflight++;
        }
-       fp->f_cred->user->unix_inflight++;
+       user->unix_inflight++;
        spin_unlock(&unix_gc_lock);
 }
 
-void unix_notinflight(struct file *fp)
+void unix_notinflight(struct user_struct *user, struct file *fp)
 {
        struct sock *s = unix_get_socket(fp);
 
@@ -155,7 +155,7 @@ void unix_notinflight(struct file *fp)
                        list_del_init(&u->link);
                unix_tot_inflight--;
        }
-       fp->f_cred->user->unix_inflight--;
+       user->unix_inflight--;
        spin_unlock(&unix_gc_lock);
 }