While converting ioctx index from a list to a table, db446a08c23d ("aio: convert the ioctx list to table lookup v3") missed tagging kioctx_table->table[] as an array of RCU pointers and using the appropriate RCU accessors. This introduces a small window in the lookup path where init and access may race.
Mark kioctx_table->table[] with __rcu and use the approriate RCU accessors when using the field.
Signed-off-by: Tejun Heo tj@kernel.org Reported-by: Jann Horn jannh@google.com Fixes: db446a08c23d ("aio: convert the ioctx list to table lookup v3") Cc: Benjamin LaHaise bcrl@kvack.org Cc: Linus Torvalds torvalds@linux-foundation.org Cc: stable@vger.kernel.org --- fs/aio.c | 21 +++++++++++---------- 1 file changed, 11 insertions(+), 10 deletions(-)
diff --git a/fs/aio.c b/fs/aio.c index eb2e0cf..6bcd3fb 100644 --- a/fs/aio.c +++ b/fs/aio.c @@ -68,9 +68,9 @@ struct aio_ring { #define AIO_RING_PAGES 8
struct kioctx_table { - struct rcu_head rcu; - unsigned nr; - struct kioctx *table[]; + struct rcu_head rcu; + unsigned nr; + struct kioctx __rcu *table[]; };
struct kioctx_cpu { @@ -330,7 +330,7 @@ static int aio_ring_mremap(struct vm_area_struct *vma) for (i = 0; i < table->nr; i++) { struct kioctx *ctx;
- ctx = table->table[i]; + ctx = rcu_dereference(table->table[i]); if (ctx && ctx->aio_ring_file == file) { if (!atomic_read(&ctx->dead)) { ctx->user_id = ctx->mmap_base = vma->vm_start; @@ -666,9 +666,9 @@ static int ioctx_add_table(struct kioctx *ctx, struct mm_struct *mm) while (1) { if (table) for (i = 0; i < table->nr; i++) - if (!table->table[i]) { + if (!rcu_access_pointer(table->table[i])) { ctx->id = i; - table->table[i] = ctx; + rcu_assign_pointer(table->table[i], ctx); spin_unlock(&mm->ioctx_lock);
/* While kioctx setup is in progress, @@ -849,8 +849,8 @@ static int kill_ioctx(struct mm_struct *mm, struct kioctx *ctx, }
table = rcu_dereference_raw(mm->ioctx_table); - WARN_ON(ctx != table->table[ctx->id]); - table->table[ctx->id] = NULL; + WARN_ON(ctx != rcu_access_pointer(table->table[ctx->id])); + RCU_INIT_POINTER(table->table[ctx->id], NULL); spin_unlock(&mm->ioctx_lock);
/* free_ioctx_reqs() will do the necessary RCU synchronization */ @@ -895,7 +895,8 @@ void exit_aio(struct mm_struct *mm)
skipped = 0; for (i = 0; i < table->nr; ++i) { - struct kioctx *ctx = table->table[i]; + struct kioctx *ctx = + rcu_dereference_protected(table->table[i], true);
if (!ctx) { skipped++; @@ -1084,7 +1085,7 @@ static struct kioctx *lookup_ioctx(unsigned long ctx_id) if (!table || id >= table->nr) goto out;
- ctx = table->table[id]; + ctx = rcu_dereference(table->table[id]); if (ctx && ctx->user_id == ctx_id) { percpu_ref_get(&ctx->users); ret = ctx;