5.4-stable review patch. If anyone has any objections, please let me know.
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From: Thadeu Lima de Souza Cascardo cascardo@igalia.com
commit a26ff37e624d12e28077e5b24d2b264f62764ad6 upstream.
net_alloc_generic is called by net_alloc, which is called without any locking. It reads max_gen_ptrs, which is changed under pernet_ops_rwsem. It is read twice, first to allocate an array, then to set s.len, which is later used to limit the bounds of the array access.
It is possible that the array is allocated and another thread is registering a new pernet ops, increments max_gen_ptrs, which is then used to set s.len with a larger than allocated length for the variable array.
Fix it by reading max_gen_ptrs only once in net_alloc_generic. If max_gen_ptrs is later incremented, it will be caught in net_assign_generic.
Signed-off-by: Thadeu Lima de Souza Cascardo cascardo@igalia.com Fixes: 073862ba5d24 ("netns: fix net_alloc_generic()") Reviewed-by: Eric Dumazet edumazet@google.com Reviewed-by: Kuniyuki Iwashima kuniyu@amazon.com Cc: stable@vger.kernel.org Link: https://lore.kernel.org/r/20240502132006.3430840-1-cascardo@igalia.com Signed-off-by: Paolo Abeni pabeni@redhat.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- net/core/net_namespace.c | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-)
--- a/net/core/net_namespace.c +++ b/net/core/net_namespace.c @@ -71,12 +71,15 @@ static unsigned int max_gen_ptrs = INITI
static struct net_generic *net_alloc_generic(void) { + unsigned int gen_ptrs = READ_ONCE(max_gen_ptrs); + unsigned int generic_size; struct net_generic *ng; - unsigned int generic_size = offsetof(struct net_generic, ptr[max_gen_ptrs]); + + generic_size = offsetof(struct net_generic, ptr[gen_ptrs]);
ng = kzalloc(generic_size, GFP_KERNEL); if (ng) - ng->s.len = max_gen_ptrs; + ng->s.len = gen_ptrs;
return ng; } @@ -1231,7 +1234,11 @@ static int register_pernet_operations(st if (error < 0) return error; *ops->id = error; - max_gen_ptrs = max(max_gen_ptrs, *ops->id + 1); + /* This does not require READ_ONCE as writers already hold + * pernet_ops_rwsem. But WRITE_ONCE is needed to protect + * net_alloc_generic. + */ + WRITE_ONCE(max_gen_ptrs, max(max_gen_ptrs, *ops->id + 1)); } error = __register_pernet_operations(list, ops); if (error) {