Commit 415e3d3e authored by Hannes Frederic Sowa's avatar Hannes Frederic Sowa Committed by David S. Miller
Browse files

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: 712f4aad ("unix: properly account for FDs passed over unix sockets")
Reported-by: default avatarDavid 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: default avatarLinus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: default avatarHannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent aa7b4537

include/net/af_unix.h

+2 −2
Original line number Diff line number Diff line
@@ -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);

include/net/scm.h

+1 −0
Original line number Diff line number Diff line
@@ -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];

};

net/core/scm.c

+7 −0
Original line number Diff line number Diff line
@@ -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;

}

net/unix/af_unix.c

+2 −2
Original line number Diff line number Diff line
@@ -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;

}

net/unix/garbage.c

+4 −4
Original line number Diff line number Diff line
@@ -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);

}

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