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[mptcp-net,7/9] sctp: sysctl: udp_port: avoid using current->nsproxy

Message ID 20250107-mptcp-sysfs-netns-v1-7-2fa7075d9970@kernel.org (mailing list archive)
State Accepted
Commit c45cb99c9aa0a885f253fc6ac8583d338bf80cbc
Delegated to: Matthieu Baerts
Headers show
Series net: sysctl: avoid using current->nsproxy | expand

Checks

Context Check Description
matttbe/build success Build and static analysis OK
matttbe/checkpatch success total: 0 errors, 0 warnings, 0 checks, 8 lines checked
matttbe/shellcheck success MPTCP selftests files have not been modified
matttbe/KVM_Validation__normal success Success! ✅
matttbe/KVM_Validation__debug success Success! ✅
matttbe/KVM_Validation__btf-normal__only_bpftest_all_ success Success! ✅
matttbe/KVM_Validation__btf-debug__only_bpftest_all_ success Success! ✅

Commit Message

Matthieu Baerts Jan. 7, 2025, 5:09 p.m. UTC
As mentioned in a previous commit of this series, using the 'net'
structure via 'current' is not recommended for different reasons:

- Inconsistency: getting info from the reader's/writer's netns vs only
  from the opener's netns.

- current->nsproxy can be NULL in some cases, resulting in an 'Oops'
  (null-ptr-deref), e.g. when the current task is exiting, as spotted by
  syzbot [1] using acct(2).

The 'net' structure can be obtained from the table->data using
container_of().

Note that table->data could also be used directly, but that would
increase the size of this fix, while 'sctp.ctl_sock' still needs to be
retrieved from 'net' structure.

Fixes: 046c052b475e ("sctp: enable udp tunneling socks")
Link: https://lore.kernel.org/67769ecb.050a0220.3a8527.003f.GAE@google.com [1]
Suggested-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
 net/sctp/sysctl.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
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Patch

diff --git a/net/sctp/sysctl.c b/net/sctp/sysctl.c
index 9d29611621feaf0d2e8d7c923601ab374515563b..18fa4f44e8ec8c86f8415b1251ef8a2979c7f823 100644
--- a/net/sctp/sysctl.c
+++ b/net/sctp/sysctl.c
@@ -528,7 +528,7 @@  static int proc_sctp_do_auth(const struct ctl_table *ctl, int write,
 static int proc_sctp_do_udp_port(const struct ctl_table *ctl, int write,
 				 void *buffer, size_t *lenp, loff_t *ppos)
 {
-	struct net *net = current->nsproxy->net_ns;
+	struct net *net = container_of(ctl->data, struct net, sctp.udp_port);
 	unsigned int min = *(unsigned int *)ctl->extra1;
 	unsigned int max = *(unsigned int *)ctl->extra2;
 	struct ctl_table tbl;