diff mbox series

[net] af_unix: annote lockless accesses to unix_tot_inflight & gc_in_progress

Message ID 20220114164328.2038499-1-eric.dumazet@gmail.com (mailing list archive)
State Accepted
Commit 9d6d7f1cb67cdee15f1a0e85aacfb924e0e02435
Delegated to: Netdev Maintainers
Headers show
Series [net] af_unix: annote lockless accesses to unix_tot_inflight & gc_in_progress | expand

Checks

Context Check Description
netdev/tree_selection success Clearly marked for net
netdev/fixes_present success Fixes tag present in non-next series
netdev/subject_prefix success Link
netdev/cover_letter success Single patches do not need cover letters
netdev/patch_count success Link
netdev/header_inline success No static functions without inline keyword in header files
netdev/build_32bit success Errors and warnings before: 2 this patch: 2
netdev/cc_maintainers success CCed 4 of 4 maintainers
netdev/build_clang success Errors and warnings before: 22 this patch: 22
netdev/module_param success Was 0 now: 0
netdev/verify_signedoff success Signed-off-by tag matches author and committer
netdev/verify_fixes success Fixes tag looks correct
netdev/build_allmodconfig_warn success Errors and warnings before: 7 this patch: 7
netdev/checkpatch warning WARNING: Possible repeated word: 'Google'
netdev/kdoc success Errors and warnings before: 0 this patch: 0
netdev/source_inline success Was 0 now: 0

Commit Message

Eric Dumazet Jan. 14, 2022, 4:43 p.m. UTC 
From: Eric Dumazet <edumazet@google.com>

wait_for_unix_gc() reads unix_tot_inflight & gc_in_progress
without synchronization.

Adds READ_ONCE()/WRITE_ONCE() and their associated comments
to better document the intent.

BUG: KCSAN: data-race in unix_inflight / wait_for_unix_gc

write to 0xffffffff86e2b7c0 of 4 bytes by task 9380 on cpu 0:
 unix_inflight+0x1e8/0x260 net/unix/scm.c:63
 unix_attach_fds+0x10c/0x1e0 net/unix/scm.c:121
 unix_scm_to_skb net/unix/af_unix.c:1674 [inline]
 unix_dgram_sendmsg+0x679/0x16b0 net/unix/af_unix.c:1817
 unix_seqpacket_sendmsg+0xcc/0x110 net/unix/af_unix.c:2258
 sock_sendmsg_nosec net/socket.c:704 [inline]
 sock_sendmsg net/socket.c:724 [inline]
 ____sys_sendmsg+0x39a/0x510 net/socket.c:2409
 ___sys_sendmsg net/socket.c:2463 [inline]
 __sys_sendmmsg+0x267/0x4c0 net/socket.c:2549
 __do_sys_sendmmsg net/socket.c:2578 [inline]
 __se_sys_sendmmsg net/socket.c:2575 [inline]
 __x64_sys_sendmmsg+0x53/0x60 net/socket.c:2575
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x44/0xd0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffffffff86e2b7c0 of 4 bytes by task 9375 on cpu 1:
 wait_for_unix_gc+0x24/0x160 net/unix/garbage.c:196
 unix_dgram_sendmsg+0x8e/0x16b0 net/unix/af_unix.c:1772
 unix_seqpacket_sendmsg+0xcc/0x110 net/unix/af_unix.c:2258
 sock_sendmsg_nosec net/socket.c:704 [inline]
 sock_sendmsg net/socket.c:724 [inline]
 ____sys_sendmsg+0x39a/0x510 net/socket.c:2409
 ___sys_sendmsg net/socket.c:2463 [inline]
 __sys_sendmmsg+0x267/0x4c0 net/socket.c:2549
 __do_sys_sendmmsg net/socket.c:2578 [inline]
 __se_sys_sendmmsg net/socket.c:2575 [inline]
 __x64_sys_sendmmsg+0x53/0x60 net/socket.c:2575
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x44/0xd0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

value changed: 0x00000002 -> 0x00000004

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 9375 Comm: syz-executor.1 Not tainted 5.16.0-rc7-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011

Fixes: 9915672d4127 ("af_unix: limit unix_tot_inflight")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: syzbot <syzkaller@googlegroups.com>
---
 net/unix/garbage.c | 14 +++++++++++---
 net/unix/scm.c     |  6 ++++--
 2 files changed, 15 insertions(+), 5 deletions(-)

Comments

patchwork-bot+netdevbpf@kernel.org Jan. 15, 2022, 2:40 a.m. UTC | #1 
Hello:

This patch was applied to netdev/net.git (master)
by Jakub Kicinski <kuba@kernel.org>:

On Fri, 14 Jan 2022 08:43:28 -0800 you wrote:
> From: Eric Dumazet <edumazet@google.com>
> 
> wait_for_unix_gc() reads unix_tot_inflight & gc_in_progress
> without synchronization.
> 
> Adds READ_ONCE()/WRITE_ONCE() and their associated comments
> to better document the intent.
> 
> [...]

Here is the summary with links:
  - [net] af_unix: annote lockless accesses to unix_tot_inflight & gc_in_progress
    https://git.kernel.org/netdev/net/c/9d6d7f1cb67c

You are awesome, thank you!
diff mbox series

Patch

diff --git a/net/unix/garbage.c b/net/unix/garbage.c
index 12e2ddaf887f204a091f157905f270046fc384a6..d45d5366115a769b21bfc1db5a67f7d53c3fa9b8 100644
--- a/net/unix/garbage.c
+++ b/net/unix/garbage.c
@@ -192,8 +192,11 @@  void wait_for_unix_gc(void)
 {
 	/* If number of inflight sockets is insane,
 	 * force a garbage collect right now.
+	 * Paired with the WRITE_ONCE() in unix_inflight(),
+	 * unix_notinflight() and gc_in_progress().
 	 */
-	if (unix_tot_inflight > UNIX_INFLIGHT_TRIGGER_GC && !gc_in_progress)
+	if (READ_ONCE(unix_tot_inflight) > UNIX_INFLIGHT_TRIGGER_GC &&
+	    !READ_ONCE(gc_in_progress))
 		unix_gc();
 	wait_event(unix_gc_wait, gc_in_progress == false);
 }
@@ -213,7 +216,9 @@  void unix_gc(void)
 	if (gc_in_progress)
 		goto out;
 
-	gc_in_progress = true;
+	/* Paired with READ_ONCE() in wait_for_unix_gc(). */
+	WRITE_ONCE(gc_in_progress, true);
+
 	/* First, select candidates for garbage collection.  Only
 	 * in-flight sockets are considered, and from those only ones
 	 * which don't have any external reference.
@@ -299,7 +304,10 @@  void unix_gc(void)
 
 	/* All candidates should have been detached by now. */
 	BUG_ON(!list_empty(&gc_candidates));
-	gc_in_progress = false;
+
+	/* Paired with READ_ONCE() in wait_for_unix_gc(). */
+	WRITE_ONCE(gc_in_progress, false);
+
 	wake_up(&unix_gc_wait);
 
  out:
diff --git a/net/unix/scm.c b/net/unix/scm.c
index 052ae709ce2899e74ebb005d8886e42ccbf8b849..aa27a02478dc1a7e4022f77e6ea7ac55f40b95c7 100644
--- a/net/unix/scm.c
+++ b/net/unix/scm.c
@@ -60,7 +60,8 @@  void unix_inflight(struct user_struct *user, struct file *fp)
 		} else {
 			BUG_ON(list_empty(&u->link));
 		}
-		unix_tot_inflight++;
+		/* Paired with READ_ONCE() in wait_for_unix_gc() */
+		WRITE_ONCE(unix_tot_inflight, unix_tot_inflight + 1);
 	}
 	user->unix_inflight++;
 	spin_unlock(&unix_gc_lock);
@@ -80,7 +81,8 @@  void unix_notinflight(struct user_struct *user, struct file *fp)
 
 		if (atomic_long_dec_and_test(&u->inflight))
 			list_del_init(&u->link);
-		unix_tot_inflight--;
+		/* Paired with READ_ONCE() in wait_for_unix_gc() */
+		WRITE_ONCE(unix_tot_inflight, unix_tot_inflight - 1);
 	}
 	user->unix_inflight--;
 	spin_unlock(&unix_gc_lock);