afs: Fix permit refcounting (1bcab125) · Commits · 戴 / test

Fix four refcount bugs in afs_cache_permit(): (1) When checking the result of the kzalloc(), we can't just return, but must put 'permits'. (2) We shouldn't put permits immediately after hashing a new permit as we need to keep the pointer stable so that we can check to see if vnode->permit_cache has changed before we decide whether to assign to it. (3) 'permits' is being put twice. (4) We need to put either the replacement or the thing replaced after the assignment to vnode->permit_cache. Without this, lots of the following are seen: Kernel BUG at ffffffffa039857b [verbose debug info unavailable] ------------[ cut here ]------------ Kernel BUG at ffffffffa039858a [verbose debug info unavailable] ------------[ cut here ]------------ The addresses are in the .text..refcount section of the kafs.ko module. Following the relocation records for the __ex_table section shows one to be due to the decrement in afs_put_permits() and the other to be key_get() in afs_cache_permit(). Occasionally, the following is seen: refcount_t overflow at afs_cache_permit+0x57d/0x5c0 [kafs] in cc1[562], uid/euid: 0/0 WARNING: CPU: 0 PID: 562 at kernel/panic.c:657 refcount_error_report+0x9c/0xac ... Reported-by:

Marc Dionne <marc.dionne@auristor.com> Signed-off-by:

David Howells <dhowells@redhat.com> Tested-by:

Marc Dionne <marc.dionne@auristor.com>

fs/afs/security.c

+10 −8

Original line number	Diff line number	Diff line
		@@ -120,7 +120,7 @@ static void afs_hash_permits(struct afs_permits *permits)
		void afs_cache_permit(struct afs_vnode vnode, struct key key,
		unsigned int cb_break)
		{
		struct afs_permits permits, xpermits, replacement, new = NULL;
		struct afs_permits permits, xpermits, replacement, zap, *new = NULL;
		afs_access_t caller_access = READ_ONCE(vnode->status.caller_access);
		size_t size = 0;
		bool changed = false;
		@@ -204,7 +204,7 @@ void afs_cache_permit(struct afs_vnode vnode, struct key key,
		new = kzalloc(sizeof(struct afs_permits) +
		sizeof(struct afs_permit) * size, GFP_NOFS);
		if (!new)
		return;
		goto out_put;

		refcount_set(&new->usage, 1);
		new->nr_permits = size;
		@@ -229,8 +229,6 @@ void afs_cache_permit(struct afs_vnode vnode, struct key key,

		afs_hash_permits(new);

		afs_put_permits(permits);

		/* Now see if the permit list we want is actually already available */
		spin_lock(&afs_permits_lock);

		@@ -262,11 +260,15 @@ found:
		kfree(new);

		spin_lock(&vnode->lock);
		if (cb_break != (vnode->cb_break + vnode->cb_interest->server->cb_s_break) \|\|
		permits != rcu_access_pointer(vnode->permit_cache))
		goto someone_else_changed_it_unlock;
		zap = rcu_access_pointer(vnode->permit_cache);
		if (cb_break == (vnode->cb_break + vnode->cb_interest->server->cb_s_break) &&
		zap == permits)
		rcu_assign_pointer(vnode->permit_cache, replacement);
		else
		zap = replacement;
		spin_unlock(&vnode->lock);
		afs_put_permits(zap);
		out_put:
		afs_put_permits(permits);
		return;

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