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fuse: fix UAF in rcu pathwalks 

->permission(), ->get_link() and ->inode_get_acl() might dereference
->s_fs_info (and, in case of ->permission(), ->s_fs_info->fc->user_ns
as well) when called from rcu pathwalk.

Freeing ->s_fs_info->fc is rcu-delayed; we need to make freeing ->s_fs_info
and dropping ->user_ns rcu-delayed too.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro 2023-09-28 00:19:39 -04:00
parent e31f0a57ae
commit 053fc4f755
3 changed files with 13 additions and 6 deletions
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3
fs/fuse/cuse.c
View File

@ -474,8 +474,7 @@ err:
static void cuse_fc_release(struct fuse_conn *fc)
{
struct cuse_conn *cc = fc_to_cc(fc);
kfree_rcu(cc, fc.rcu);
kfree(fc_to_cc(fc));
}
/**

1
fs/fuse/fuse_i.h
View File

@ -888,6 +888,7 @@ struct fuse_mount {
/* Entry on fc->mounts */
struct list_head fc_entry;
struct rcu_head rcu;
};
static inline struct fuse_mount *get_fuse_mount_super(struct super_block *sb)

15
fs/fuse/inode.c
View File

@ -930,6 +930,14 @@ void fuse_conn_init(struct fuse_conn *fc, struct fuse_mount *fm,
}
EXPORT_SYMBOL_GPL(fuse_conn_init);
static void delayed_release(struct rcu_head *p)
{
struct fuse_conn *fc = container_of(p, struct fuse_conn, rcu);
put_user_ns(fc->user_ns);
fc->release(fc);
}
void fuse_conn_put(struct fuse_conn *fc)
{
if (refcount_dec_and_test(&fc->count)) {
@ -941,13 +949,12 @@ void fuse_conn_put(struct fuse_conn *fc)
if (fiq->ops->release)
fiq->ops->release(fiq);
put_pid_ns(fc->pid_ns);
put_user_ns(fc->user_ns);
bucket = rcu_dereference_protected(fc->curr_bucket, 1);
if (bucket) {
WARN_ON(atomic_read(&bucket->count) != 1);
kfree(bucket);
}
fc->release(fc);
call_rcu(&fc->rcu, delayed_release);
}
}
EXPORT_SYMBOL_GPL(fuse_conn_put);
@ -1366,7 +1373,7 @@ EXPORT_SYMBOL_GPL(fuse_send_init);
void fuse_free_conn(struct fuse_conn *fc)
{
WARN_ON(!list_empty(&fc->devices));
kfree_rcu(fc, rcu);
kfree(fc);
}
EXPORT_SYMBOL_GPL(fuse_free_conn);
@ -1902,7 +1909,7 @@ static void fuse_sb_destroy(struct super_block *sb)
void fuse_mount_destroy(struct fuse_mount *fm)
{
fuse_conn_put(fm->fc);
kfree(fm);
kfree_rcu(fm, rcu);
}
EXPORT_SYMBOL(fuse_mount_destroy);