[PATCH AUTOSEL 3.18 98/98] unix: correctly track in-flight fds in sending process user_struct

Sasha Levin
2018-10-25T14:18:53Z

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

[ Upstream commit 415e3d3e90ce9e18727e8843ae343eda5a58fad6 ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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 e830c3dff61a..7bb69c9c3c43 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 d30eb057fa7b..cad57a1390dd 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);
}
}
@@ -337,6 +343,7 @@ 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 29b1f4dc48ca..1bd4ba6b6aa4 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -1469,7 +1469,7 @@ 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)
@@ -1534,7 +1534,7 @@ 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 58783dcfd35d..1105a60468ac 100644
--- 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);

@@ -139,11 +139,11 @@ 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);

@@ -158,7 +158,7 @@ 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);
}

--
2.17.1