FAILED: patch "[PATCH] io_uring: Fix a null-ptr-deref in io_tctx_exit_cb()" failed to apply to 5.15-stable tree

PATCH [email protected] 2 participants 3 messages Dec 11, 2022 – Dec 12, 2022

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[email protected]

author maintainer

2022-12-11 09:51 UTC #0 lore raw

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

Possible dependencies:

998b30c3948e ("io_uring: Fix a null-ptr-deref in io_tctx_exit_cb()") ed29b0b4fd83 ("io_uring: move to separate directory") 4c928904ff77 ("block: move CONFIG_BLOCK guard to top Makefile")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 998b30c3948e4d0b1097e639918c5cff332acac5 Mon Sep 17 00:00:00 2001
From: Harshit Mogalapalli <[email protected]>
Date: Tue, 6 Dec 2022 01:38:32 -0800
Subject: [PATCH] io_uring: Fix a null-ptr-deref in io_tctx_exit_cb()

Syzkaller reports a NULL deref bug as follows:

 BUG: KASAN: null-ptr-deref in io_tctx_exit_cb+0x53/0xd3
 Read of size 4 at addr 0000000000000138 by task file1/1955

 CPU: 1 PID: 1955 Comm: file1 Not tainted 6.1.0-rc7-00103-gef4d3ea40565 #75
 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.11.0-2.el7 04/01/2014
 Call Trace:
  <TASK>
  dump_stack_lvl+0xcd/0x134
  ? io_tctx_exit_cb+0x53/0xd3
  kasan_report+0xbb/0x1f0
  ? io_tctx_exit_cb+0x53/0xd3
  kasan_check_range+0x140/0x190
  io_tctx_exit_cb+0x53/0xd3
  task_work_run+0x164/0x250
  ? task_work_cancel+0x30/0x30
  get_signal+0x1c3/0x2440
  ? lock_downgrade+0x6e0/0x6e0
  ? lock_downgrade+0x6e0/0x6e0
  ? exit_signals+0x8b0/0x8b0
  ? do_raw_read_unlock+0x3b/0x70
  ? do_raw_spin_unlock+0x50/0x230
  arch_do_signal_or_restart+0x82/0x2470
  ? kmem_cache_free+0x260/0x4b0
  ? putname+0xfe/0x140
  ? get_sigframe_size+0x10/0x10
  ? do_execveat_common.isra.0+0x226/0x710
  ? lockdep_hardirqs_on+0x79/0x100
  ? putname+0xfe/0x140
  ? do_execveat_common.isra.0+0x238/0x710
  exit_to_user_mode_prepare+0x15f/0x250
  syscall_exit_to_user_mode+0x19/0x50
  do_syscall_64+0x42/0xb0
  entry_SYSCALL_64_after_hwframe+0x63/0xcd
 RIP: 0023:0x0
 Code: Unable to access opcode bytes at 0xffffffffffffffd6.
 RSP: 002b:00000000fffb7790 EFLAGS: 00000200 ORIG_RAX: 000000000000000b
 RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
 RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
 RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
 R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
 R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
  </TASK>
 Kernel panic - not syncing: panic_on_warn set ...

This happens because the adding of task_work from io_ring_exit_work() isn't synchronized with canceling all work items from eg exec. The execution of the two are ordered in that they are both run by the task itself, but if io_tctx_exit_cb() is queued while we're canceling all work items off exec AND gets executed when the task exits to userspace rather than in the main loop in io_uring_cancel_generic(), then we can find current->io_uring == NULL and hit the above crash.

It's safe to add this NULL check here, because the execution of the two paths are done by the task itself.

Cc [email protected]

Fixes d56d938b4bef ("io_uring: do ctx initiated file note removal")

Reported-by syzkaller <[email protected]>

Signed-off-by Harshit Mogalapalli <[email protected]>

Link https://lore.kernel.org/r/[email protected] open here

[axboe: add code comment and also put an explanation in the commit msg]

Signed-off-by Jens Axboe <[email protected]>

io_uring/io_uring.c +3 -1

index 8840cf3e20f2..61cd7ffd0f6a 100644
@@ -2707,8 +2707,10 @@ static __cold void io_tctx_exit_cb(struct callback_head *cb)
 	/*
 	 * When @in_idle, we're in cancellation and it's racy to remove the
 	 * node. It'll be removed by the end of cancellation, just ignore it.
+	 * tctx can be NULL if the queueing of this task_work raced with
+	 * work cancelation off the exec path.
 	 */
-	if (!atomic_read(&tctx->in_idle))
+	if (tctx && !atomic_read(&tctx->in_idle))
 		io_uring_del_tctx_node((unsigned long)work->ctx);
 	complete(&work->completion);
 }

Jens Axboe

maintainer

2022-12-11 17:33 UTC #1 lore raw

Quoted 5 lines · On 12/11/22 2:51?AM, [email protected] wrote:

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

It does apply fine, but it's in fs/io_uring.c rather than io_uring/io_uring.c as for the newer kernels. Attached one here that just does the patch change and it applies witha a slight offset:

checking file fs/io_uring.c
Hunk #1 succeeded at 9467 (offset 6760 lines).

Syzkaller reports a NULL deref bug as follows:

 BUG: KASAN: null-ptr-deref in io_tctx_exit_cb+0x53/0xd3
 Read of size 4 at addr 0000000000000138 by task file1/1955

 CPU: 1 PID: 1955 Comm: file1 Not tainted 6.1.0-rc7-00103-gef4d3ea40565 #75
 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.11.0-2.el7 04/01/2014
 Call Trace:
  <TASK>
  dump_stack_lvl+0xcd/0x134
  ? io_tctx_exit_cb+0x53/0xd3
  kasan_report+0xbb/0x1f0
  ? io_tctx_exit_cb+0x53/0xd3
  kasan_check_range+0x140/0x190
  io_tctx_exit_cb+0x53/0xd3
  task_work_run+0x164/0x250
  ? task_work_cancel+0x30/0x30
  get_signal+0x1c3/0x2440
  ? lock_downgrade+0x6e0/0x6e0
  ? lock_downgrade+0x6e0/0x6e0
  ? exit_signals+0x8b0/0x8b0
  ? do_raw_read_unlock+0x3b/0x70
  ? do_raw_spin_unlock+0x50/0x230
  arch_do_signal_or_restart+0x82/0x2470
  ? kmem_cache_free+0x260/0x4b0
  ? putname+0xfe/0x140
  ? get_sigframe_size+0x10/0x10
  ? do_execveat_common.isra.0+0x226/0x710
  ? lockdep_hardirqs_on+0x79/0x100
  ? putname+0xfe/0x140
  ? do_execveat_common.isra.0+0x238/0x710
  exit_to_user_mode_prepare+0x15f/0x250
  syscall_exit_to_user_mode+0x19/0x50
  do_syscall_64+0x42/0xb0
  entry_SYSCALL_64_after_hwframe+0x63/0xcd
 RIP: 0023:0x0
 Code: Unable to access opcode bytes at 0xffffffffffffffd6.
 RSP: 002b:00000000fffb7790 EFLAGS: 00000200 ORIG_RAX: 000000000000000b
 RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
 RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
 RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
 R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
 R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
  </TASK>
 Kernel panic - not syncing: panic_on_warn set ...

It's safe to add this NULL check here, because the execution of the two paths are done by the task itself.

Cc [email protected]

Fixes d56d938b4bef ("io_uring: do ctx initiated file note removal")

Reported-by syzkaller <[email protected]>

Signed-off-by Harshit Mogalapalli <[email protected]>

Link https://lore.kernel.org/r/[email protected] open here

[axboe: add code comment and also put an explanation in the commit msg]

Signed-off-by Jens Axboe <[email protected]>

fs/io_uring.c +3 -1

index 8840cf3e20f2..61cd7ffd0f6a 100644
@@ -2707,8 +2707,10 @@ static __cold void io_tctx_exit_cb(struct callback_head *cb)
 	/*
 	 * When @in_idle, we're in cancellation and it's racy to remove the
 	 * node. It'll be removed by the end of cancellation, just ignore it.
+	 * tctx can be NULL if the queueing of this task_work raced with
+	 * work cancelation off the exec path.
 	 */
-	if (!atomic_read(&tctx->in_idle))
+	if (tctx && !atomic_read(&tctx->in_idle))
 		io_uring_del_tctx_node((unsigned long)work->ctx);
 	complete(&work->completion);
 }

Signature · 1 line

Jens Axboe

Greg KH

author maintainer

2022-12-12 08:04 UTC #2 lore raw

Quoted 11 lines · Jens Axboe

Quoted 5 lines · On 12/11/22 2:51?AM, [email protected] wrote:
The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.
It does apply fine, but it's in fs/io_uring.c rather than io_uring/io_uring.c as for the newer kernels. Attached one here that just does the patch change and it applies witha a slight offset:

Sorry, my fault, I should have caught this. Thanks for the backport!

greg k-h