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>
diff --git a/net/core/scm.c b/net/core/scm.c
index 14596fb..2696aef 100644
--- a/net/core/scm.c
+++ b/net/core/scm.c
@@ -87,6 +87,7 @@
*fplp = fpl;
fpl->count = 0;
fpl->max = SCM_MAX_FD;
+ fpl->user = NULL;
}
fpp = &fpl->fp[fpl->count];
@@ -107,6 +108,10 @@
*fpp++ = file;
fpl->count++;
}
+
+ if (!fpl->user)
+ fpl->user = get_uid(current_user());
+
return num;
}
@@ -119,6 +124,7 @@
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 @@
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;
}