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On Sat, Aug 1, 2026 at 7: 09 AM Kuniyuki Iwashima <kuniyu@ google. com> wrote: > > From: Chengfeng Ye <nicoyip. dev@ gmail. com> > Date: Sat, 1 Aug 2026 00: 09: 42 +0800 > > rds_info_getsockopt() reads a callback from rds_info_funcs</div>
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</head><body><pre style="font-family: sans-serif; font-size: 100%; white-space: pre-wrap; word-wrap: break-word">On Sat, Aug 1, 2026 at 7:09 AM Kuniyuki Iwashima <kuniyu@google.com> wrote:
>
> From: Chengfeng Ye <nicoyip.dev@gmail.com>
> Date: Sat, 1 Aug 2026 00:09:42 +0800
> > rds_info_getsockopt() reads a callback from rds_info_funcs and invokes it
> > without protecting the callback's lifetime. Transport modules register
> > functions stored in this array. For example, rds_tcp.ko registers
> > rds_tcp_tc_info() for RDS_INFO_TCP_SOCKETS.
> >
> > This permits the following interleaving:
> >
> > CPU0 CPU1
> > rds_info_getsockopt()
> > func = rds_tcp_tc_info
> > rmmod rds_tcp
> > rds_tcp_exit()
> > rds_info_deregister_func()
> > rds_info_funcs[offset] = NULL
> > free rds_tcp module text
> > func()
> >
> > The reader can therefore branch to an address in unloaded module text.
> >
> > Protect callback invocation with SRCU. Enter the SRCU read-side critical
> > section before loading the callback and leave it only after the callback
> > returns. Clear the callback with release semantics and call
> > synchronize_srcu() before deregistration returns, preventing module unload
> > from freeing its text while an old reader is still executing it. SRCU is
> > required because callbacks such as RDS_INFO_COUNTERS can sleep.
> >
> > Keep the callback array unannotated and use acquire and release operations
> > for publication so sparse does not have to apply __rcu through the
> > function-pointer typedef. Replace the two callback-slot BUG_ON() checks
> > with WARN_ON_ONCE() and return without changing the slot on mismatch.
> >
> > Link: https://lore.kernel.org/netdev/20260720184955.3008978-1-nicoyip.dev@gmail.com/
> > Suggested-by: Allison Henderson <achender@kernel.org>
> > Reviewed-by: Allison Henderson <achender@kernel.org>
> > Signed-off-by: Chengfeng Ye <nicoyip.dev@gmail.com>
> > ---
> >
> > Changes in v3:
> > - Use ordinary loads for callback-slot validation under rds_info_lock;
> > retain acquire semantics only for the lockless reader.
> > - Drop the Fixes tag because this patch targets net-next.
> > - Add Allison Henderson's Reviewed-by tag.
> >
> > Link: https://lore.kernel.org/netdev/20260727174826.135662-1-nicoyip.dev@gmail.com/ [v2]
> >
> > Changes in v2:
> > - Split the info callback/module-unload race from the independent
> > inc->i_conn lifetime bug.
> > - Keep the callback array unannotated and use smp_load_acquire() and
> > smp_store_release() to resolve the sparse errors.
> > - Replace the two touched callback-slot BUG_ON() checks with
> > WARN_ON_ONCE() error paths.
> > - Rewrite the commit message for the callback race and omit the unrelated
> > inc->i_conn KASAN report.
> >
> > Link: https://lore.kernel.org/netdev/20260720184955.3008978-1-nicoyip.dev@gmail.com/ [v1]
> >
> > net/rds/info.c | 26 +++++++++++++++++++++-----
> > 1 file changed, 21 insertions(+), 5 deletions(-)
> >
> > diff --git a/net/rds/info.c b/net/rds/info.c
> > index 21b32eb16559..385fefbfa07f 100644
> > --- a/net/rds/info.c
> > +++ b/net/rds/info.c
> > @@ -32,6 +32,7 @@
> > */
> > #include <linux/percpu.h>
> > #include <linux/seq_file.h>
> > +#include <linux/srcu.h>
> > #include <linux/slab.h>
> > #include <linux/proc_fs.h>
> > #include <linux/export.h>
> > @@ -68,6 +69,7 @@ struct rds_info_iterator {
> > unsigned long offset;
> > };
> >
> > +DEFINE_STATIC_SRCU(rds_info_srcu);
> > static DEFINE_SPINLOCK(rds_info_lock);
> > static rds_info_func rds_info_funcs[RDS_INFO_LAST - RDS_INFO_FIRST + 1];
> >
> > @@ -78,8 +80,12 @@ void rds_info_register_func(int optname, rds_info_func func)
> > BUG_ON(optname < RDS_INFO_FIRST || optname > RDS_INFO_LAST);
> >
> > spin_lock(&rds_info_lock);
> > - BUG_ON(rds_info_funcs[offset]);
> > - rds_info_funcs[offset] = func;
> > + if (WARN_ON_ONCE(rds_info_funcs[offset])) {
> > + spin_unlock(&rds_info_lock);
> > + return;
> > + }
> > + /* Pair with lockless callback lookup. */
> > + smp_store_release(&rds_info_funcs[offset], func);
>
> Why is smp_store_release() necessary here ? and same for
> smp_load_acquire() on the reader.
>
> I think just WRITE_ONCE() / READ_ONCE() should be enough.
>
> It's just a function pointer, not struct, and the reader
> does not require any partial ordering, no ?
>
>
> > spin_unlock(&rds_info_lock);
> > }
> > EXPORT_SYMBOL_GPL(rds_info_register_func);
> > @@ -91,9 +97,14 @@ void rds_info_deregister_func(int optname, rds_info_func func)
> > BUG_ON(optname < RDS_INFO_FIRST || optname > RDS_INFO_LAST);
> >
> > spin_lock(&rds_info_lock);
> > - BUG_ON(rds_info_funcs[offset] != func);
> > - rds_info_funcs[offset] = NULL;
> > + if (WARN_ON_ONCE(rds_info_funcs[offset] != func)) {
> > + spin_unlock(&rds_info_lock);
> > + return;
> > + }
> > + /* Hide the callback before waiting for old readers. */
> > + smp_store_release(&rds_info_funcs[offset], NULL);
> > spin_unlock(&rds_info_lock);
> > + synchronize_srcu(&rds_info_srcu);
> > }
> > EXPORT_SYMBOL_GPL(rds_info_deregister_func);
> >
> > @@ -165,6 +176,7 @@ int rds_info_getsockopt(struct socket *sock, int optname, sockopt_t *opt)
> > int npages = 0;
> > int ret;
> > int len;
> > + int srcu_idx;
>
> nit: please keep the reverse xmas tree order.
Hi,
Indeed WRITE/READ_ONCE should suffice for this code, maybe we don't
need that smp store/load despite it looks more secure. I will make a
v4 patch to address it as well as the reverse xmas tree order problem.
Best Regards,
Chengfeng
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