6.8-stable review patch. If anyone has any objections, please let me know.
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From: Carlos Maiolino cem@kernel.org
commit 0a69b6b3a026543bc215ccc866d0aea5579e6ce2 upstream.
A syzkaller reproducer found a race while attempting to remove dquot information from the rb tree.
Fetching the rb_tree root node must also be protected by the dqopt->dqio_sem, otherwise, giving the right timing, shmem_release_dquot() will trigger a warning because it couldn't find a node in the tree, when the real reason was the root node changing before the search starts:
Thread 1 Thread 2 - shmem_release_dquot() - shmem_{acquire,release}_dquot()
- fetch ROOT - Fetch ROOT
- acquire dqio_sem - wait dqio_sem
- do something, triger a tree rebalance - release dqio_sem
- acquire dqio_sem - start searching for the node, but from the wrong location, missing the node, and triggering a warning.
Link: https://lkml.kernel.org/r/20240320124011.398847-1-cem@kernel.org Fixes: eafc474e2029 ("shmem: prepare shmem quota infrastructure") Signed-off-by: Carlos Maiolino cmaiolino@redhat.com Reported-by: Ubisectech Sirius bugreport@ubisectech.com Reviewed-by: Jan Kara jack@suse.cz Cc: Hugh Dickins hughd@google.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- mm/shmem_quota.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-)
--- a/mm/shmem_quota.c +++ b/mm/shmem_quota.c @@ -116,7 +116,7 @@ static int shmem_free_file_info(struct s static int shmem_get_next_id(struct super_block *sb, struct kqid *qid) { struct mem_dqinfo *info = sb_dqinfo(sb, qid->type); - struct rb_node *node = ((struct rb_root *)info->dqi_priv)->rb_node; + struct rb_node *node; qid_t id = from_kqid(&init_user_ns, *qid); struct quota_info *dqopt = sb_dqopt(sb); struct quota_id *entry = NULL; @@ -126,6 +126,7 @@ static int shmem_get_next_id(struct supe return -ESRCH;
down_read(&dqopt->dqio_sem); + node = ((struct rb_root *)info->dqi_priv)->rb_node; while (node) { entry = rb_entry(node, struct quota_id, node);
@@ -165,7 +166,7 @@ out_unlock: static int shmem_acquire_dquot(struct dquot *dquot) { struct mem_dqinfo *info = sb_dqinfo(dquot->dq_sb, dquot->dq_id.type); - struct rb_node **n = &((struct rb_root *)info->dqi_priv)->rb_node; + struct rb_node **n; struct shmem_sb_info *sbinfo = dquot->dq_sb->s_fs_info; struct rb_node *parent = NULL, *new_node = NULL; struct quota_id *new_entry, *entry; @@ -176,6 +177,8 @@ static int shmem_acquire_dquot(struct dq mutex_lock(&dquot->dq_lock);
down_write(&dqopt->dqio_sem); + n = &((struct rb_root *)info->dqi_priv)->rb_node; + while (*n) { parent = *n; entry = rb_entry(parent, struct quota_id, node); @@ -264,7 +267,7 @@ static bool shmem_is_empty_dquot(struct static int shmem_release_dquot(struct dquot *dquot) { struct mem_dqinfo *info = sb_dqinfo(dquot->dq_sb, dquot->dq_id.type); - struct rb_node *node = ((struct rb_root *)info->dqi_priv)->rb_node; + struct rb_node *node; qid_t id = from_kqid(&init_user_ns, dquot->dq_id); struct quota_info *dqopt = sb_dqopt(dquot->dq_sb); struct quota_id *entry = NULL; @@ -275,6 +278,7 @@ static int shmem_release_dquot(struct dq goto out_dqlock;
down_write(&dqopt->dqio_sem); + node = ((struct rb_root *)info->dqi_priv)->rb_node; while (node) { entry = rb_entry(node, struct quota_id, node);