On Wed, Mar 05, 2025 at 10:10:41AM -0800, Kuniyuki Iwashima wrote:
+Paolo
From: Greg Kroah-Hartman gregkh@linuxfoundation.org Date: Wed, 5 Mar 2025 15:08:26 +0100
On Mon, Mar 03, 2025 at 07:01:49PM -0800, Kuniyuki Iwashima wrote:
Embryo socket is not queued in gc_candidates, so we can't drop a reference held by its oob_skb.
Let's say we create listener and embryo sockets, send the listener's fd to the embryo as OOB data, and close() them without recv()ing the OOB data.
There is a self-reference cycle like
listener -> embryo.oob_skb -> listener
, so this must be cleaned up by GC. Otherwise, the listener's refcnt is not released and sockets are leaked:
# unshare -n # cat /proc/net/protocols | grep UNIX-STREAM UNIX-STREAM 1024 0 -1 NI 0 yes kernel ...
# python3
from array import array from socket import *
s = socket(AF_UNIX, SOCK_STREAM) s.bind('\0test\0') s.listen()
c = socket(AF_UNIX, SOCK_STREAM) c.connect(s.getsockname()) c.sendmsg([b'x'], [(SOL_SOCKET, SCM_RIGHTS, array('i', [s.fileno()]))], MSG_OOB)
1
quit()
# cat /proc/net/protocols | grep UNIX-STREAM UNIX-STREAM 1024 3 -1 NI 0 yes kernel ... ^^^ 3 sockets still in use after FDs are close()d
Let's drop the embryo socket's oob_skb ref in scan_inflight().
This also fixes a racy access to oob_skb that commit 9841991a446c ("af_unix: Update unix_sk(sk)->oob_skb under sk_receive_queue lock.") fixed for the new Tarjan's algo-based GC.
Fixes: 314001f0bf92 ("af_unix: Add OOB support") Reported-by: Lei Lu llfamsec@gmail.com Signed-off-by: Kuniyuki Iwashima kuniyu@amazon.com
This has no upstream commit because I replaced the entire GC in 6.10 and the new GC does not have this bug, and this fix is only applicable to the old GC (<= 6.9), thus for 5.15/6.1/6.6.
You need to get the networking maintainers to review and agree that this is ok for us to take, as we really don't want to take "custom" stuff like thi s at all.
Paolo, could you take a look at this patch ? https://lore.kernel.org/netdev/20250304030149.82265-1-kuniyu@amazon.com/
Why not just take the commits that are in newer kernels instead?
That will be about 20 patches that rewrite the most lines of net/unix/garbage.c and cannot be applied cleanly.
I think backporting these commits is overkill to fix a small bug that can be fixed with a much smaller diff.
927fa5b3e4f5 af_unix: Fix uninit-value in __unix_walk_scc() 041933a1ec7b af_unix: Fix garbage collection of embryos carrying OOB with SCM_RIGHTS 7172dc93d621 af_unix: Add dead flag to struct scm_fp_list. 1af2dface5d2 af_unix: Don't access successor in unix_del_edges() during GC. fd86344823b5 af_unix: Try not to hold unix_gc_lock during accept(). 118f457da9ed af_unix: Remove lock dance in unix_peek_fds(). 4090fa373f0e af_unix: Replace garbage collection algorithm. a15702d8b3aa af_unix: Detect dead SCC. bfdb01283ee8 af_unix: Assign a unique index to SCC. ad081928a8b0 af_unix: Avoid Tarjan's algorithm if unnecessary. 77e5593aebba af_unix: Skip GC if no cycle exists. ba31b4a4e101 af_unix: Save O(n) setup of Tarjan's algo. dcf70df2048d af_unix: Fix up unix_edge.successor for embryo socket. 3484f063172d af_unix: Detect Strongly Connected Components. 6ba76fd2848e af_unix: Iterate all vertices by DFS. 22c3c0c52d32 af_unix: Bulk update unix_tot_inflight/unix_inflight when queuing skb. 42f298c06b30 af_unix: Link struct unix_edge when queuing skb. 29b64e354029 af_unix: Allocate struct unix_edge for each inflight AF_UNIX fd. 1fbfdfaa5902 af_unix: Allocate struct unix_vertex for each inflight AF_UNIX fd.
Sure, but now all fixes made upstream after these changes will not apply to older kernels at all, making supporting this old one-off change harder and harder over time.
But I'll defer to the maintainers here as to what they want. Taking 20+ patches in a stable tree is trivial for us, not a problem at all.
thanks,
greg k-h