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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</div>
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</head><body><pre style="font-family: sans-serif; font-size: 100%; white-space: pre-wrap; word-wrap: break-word">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.
> int total;
>
> len = opt->optlen;
> @@ -214,8 +226,11 @@ int rds_info_getsockopt(struct socket *sock, int optname, sockopt_t *opt)
> rdsdebug("len %d nr_pages %lu\n", len, nr_pages);
>
> call_func:
> - func = rds_info_funcs[optname - RDS_INFO_FIRST];
> + srcu_idx = srcu_read_lock(&rds_info_srcu);
> + /* Pair with callback slot publication and removal. */
> + func = smp_load_acquire(&rds_info_funcs[optname - RDS_INFO_FIRST]);
> if (!func) {
> + srcu_read_unlock(&rds_info_srcu, srcu_idx);
> ret = -ENOPROTOOPT;
> goto out;
> }
> @@ -225,6 +240,7 @@ int rds_info_getsockopt(struct socket *sock, int optname, sockopt_t *opt)
> iter.offset = offset0;
>
> func(sock, len, &iter, &lens);
> + srcu_read_unlock(&rds_info_srcu, srcu_idx);
> BUG_ON(lens.each == 0);
>
> total = lens.nr * lens.each;
> --
> 2.43.0
>
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