From 415e3d3e90ce9e18727e8843ae343eda5a58fad6 Mon Sep 17 00:00:00 2001

From: Hannes Frederic Sowa <hannes@stressinduktion.org>

Date: Wed, 3 Feb 2016 02:11:03 +0100

Subject: [PATCH] unix: correctly track in-flight fds in sending process

 user_struct

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>

---

 include/net/af_unix.h | 4 ++--

 include/net/scm.h     | 1 +

 net/core/scm.c        | 7 +++++++

 net/unix/af_unix.c    | 4 ++--

 net/unix/garbage.c    | 8 ++++----

 5 files changed, 16 insertions(+), 8 deletions(-)

diff --git a/include/net/af_unix.h b/include/net/af_unix.h

index 2a91a0561a47..9b4c418bebd8 100644

--- a/include/net/af_unix.h

+++ b/include/net/af_unix.h

@@ -6,8 +6,8 @@

 #include <linux/mutex.h>

 #include <net/sock.h>

-void unix_inflight(struct file *fp);

-void unix_notinflight(struct file *fp);

+void unix_inflight(struct user_struct *user, struct file *fp);

+void unix_notinflight(struct user_struct *user, struct file *fp);

 void unix_gc(void);

 void wait_for_unix_gc(void);

 struct sock *unix_get_socket(struct file *filp);

diff --git a/include/net/scm.h b/include/net/scm.h

index 262532d111f5..59fa93c01d2a 100644

--- a/include/net/scm.h

+++ b/include/net/scm.h

@@ -21,6 +21,7 @@ struct scm_creds {

 struct scm_fp_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 14596fb37172..2696aefdc148 100644

--- a/net/core/scm.c

+++ b/net/core/scm.c

@@ -87,6 +87,7 @@ 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];

@@ -107,6 +108,10 @@ 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;

 }

@@ -119,6 +124,7 @@ void __scm_destroy(struct scm_cookie *scm)

 		scm->fp = NULL;

 		for (i=fpl->count-1; i>=0; i--)

 			fput(fpl->fp[i]);

+		free_uid(fpl->user);

 		kfree(fpl);

 	}

 }

@@ -336,6 +342,7 @@ 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 49d5093eb055..29be035f9c65 100644

--- a/net/unix/af_unix.c

+++ b/net/unix/af_unix.c

@@ -1496,7 +1496,7 @@ 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)

@@ -1561,7 +1561,7 @@ 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 8fcdc2283af5..6a0d48525fcf 100644

--- a/net/unix/garbage.c

+++ b/net/unix/garbage.c

@@ -116,7 +116,7 @@ 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);

@@ -133,11 +133,11 @@ 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);

@@ -152,7 +152,7 @@ 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);

 }

-- 

2.5.0