Re: [PATCH] ext4: fix uninitialized ratelimit_state->lock access in __ext4_fill_super()

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Hi Ted,

Would you consider merging in this patch in the current merge
window? This patch has been merged in our internal branch for
a while now and so far it is safe.

Regards,
Baokun

On 2024/4/23 9:41, Baokun Li wrote:
Gently ping again.

On 2024/1/2 21:37, Baokun Li wrote:
In the following concurrency we will access the uninitialized rs->lock:

ext4_fill_super
   ext4_register_sysfs
    // sysfs registered msg_ratelimit_interval_ms
                              // Other processes modify rs->interval to
                              // non-zero via msg_ratelimit_interval_ms
   ext4_orphan_cleanup
     ext4_msg(sb, KERN_INFO, "Errors on filesystem, "
       __ext4_msg
___ratelimit(&(EXT4_SB(sb)->s_msg_ratelimit_state)
           if (!rs->interval)  // do nothing if interval is 0
             return 1;
           raw_spin_trylock_irqsave(&rs->lock, flags)
             raw_spin_trylock(lock)
               _raw_spin_trylock
                 __raw_spin_trylock
                   spin_acquire(&lock->dep_map, 0, 1, _RET_IP_)
                     lock_acquire
                       __lock_acquire
                         register_lock_class
                           assign_lock_key
                             dump_stack();
   ratelimit_state_init(&sbi->s_msg_ratelimit_state, 5 * HZ, 10);
     raw_spin_lock_init(&rs->lock);
     // init rs->lock here

and get the following dump_stack:

=========================================================
INFO: trying to register non-static key.
The code is fine but needs lockdep annotation, or maybe
you didn't initialize this object before use?
turning off the locking correctness validator.
CPU: 12 PID: 753 Comm: mount Tainted: G E 6.7.0-rc6-next-20231222 #504
[...]
Call Trace:
  dump_stack_lvl+0xc5/0x170
  dump_stack+0x18/0x30
  register_lock_class+0x740/0x7c0
  __lock_acquire+0x69/0x13a0
  lock_acquire+0x120/0x450
  _raw_spin_trylock+0x98/0xd0
  ___ratelimit+0xf6/0x220
  __ext4_msg+0x7f/0x160 [ext4]
  ext4_orphan_cleanup+0x665/0x740 [ext4]
  __ext4_fill_super+0x21ea/0x2b10 [ext4]
  ext4_fill_super+0x14d/0x360 [ext4]
[...]
=========================================================

Normally interval is 0 until s_msg_ratelimit_state is initialized, so
___ratelimit() does nothing. But registering sysfs precedes initializing
rs->lock, so it is possible to change rs->interval to a non-zero value
via the msg_ratelimit_interval_ms interface of sysfs while rs->lock is
uninitialized, and then a call to ext4_msg triggers the problem by
accessing an uninitialized rs->lock. Therefore register sysfs after all
initializations are complete to avoid such problems.

Signed-off-by: Baokun Li <libaokun1@xxxxxxxxxx>
---
  fs/ext4/super.c | 22 ++++++++++------------
  1 file changed, 10 insertions(+), 12 deletions(-)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 0980845c8b8f..1db23b0e8a4f 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -5564,19 +5564,15 @@ static int __ext4_fill_super(struct fs_context *fc, struct super_block *sb)
      if (err)
          goto failed_mount6;
  -    err = ext4_register_sysfs(sb);
-    if (err)
-        goto failed_mount7;
-
      err = ext4_init_orphan_info(sb);
      if (err)
-        goto failed_mount8;
+        goto failed_mount7;
  #ifdef CONFIG_QUOTA
      /* Enable quota usage during mount. */
      if (ext4_has_feature_quota(sb) && !sb_rdonly(sb)) {
          err = ext4_enable_quotas(sb);
          if (err)
-            goto failed_mount9;
+            goto failed_mount8;
      }
  #endif  /* CONFIG_QUOTA */
  @@ -5602,7 +5598,7 @@ static int __ext4_fill_super(struct fs_context *fc, struct super_block *sb)
          ext4_msg(sb, KERN_INFO, "recovery complete");
          err = ext4_mark_recovery_complete(sb, es);
          if (err)
-            goto failed_mount10;
+            goto failed_mount9;
      }
        if (test_opt(sb, DISCARD) && !bdev_max_discard_sectors(sb->s_bdev)) @@ -5619,15 +5615,17 @@ static int __ext4_fill_super(struct fs_context *fc, struct super_block *sb)
      atomic_set(&sbi->s_warning_count, 0);
      atomic_set(&sbi->s_msg_count, 0);
  +    /* Register sysfs after all initializations are complete. */
+    err = ext4_register_sysfs(sb);
+    if (err)
+        goto failed_mount9;
+
      return 0;
  -failed_mount10:
+failed_mount9:
      ext4_quotas_off(sb, EXT4_MAXQUOTAS);
-failed_mount9: __maybe_unused
+failed_mount8: __maybe_unused
      ext4_release_orphan_info(sb);
-failed_mount8:
-    ext4_unregister_sysfs(sb);
-    kobject_put(&sbi->s_kobj);
  failed_mount7:
      ext4_unregister_li_request(sb);
  failed_mount6:






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