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: 712f4aad40 ("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>
This commit is contained in:
Hannes Frederic Sowa 2016-02-03 02:11:03 +01:00 committed by David S. Miller
parent aa7b453780
commit 415e3d3e90
5 changed files with 16 additions and 8 deletions

View File

@ -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);

View File

@ -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];
};

View File

@ -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;
}

View File

@ -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;
}

View File

@ -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);
}