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sctp: sysctl: cookie_hmac_alg: avoid using current->nsproxy

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commit ea62dd1383913b5999f3d16ae99d411f41b528d4 upstream.

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, as this is the only
member needed from the 'net' structure, but that would increase the size
of this fix, to use '*data' everywhere 'net->sctp.sctp_hmac_alg' is
used.

Fixes: 3c68198e75 ("sctp: Make hmac algorithm selection for cookie generation dynamic")
Cc: stable@vger.kernel.org
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>
Link: https://patch.msgid.link/20250108-net-sysctl-current-nsproxy-v1-4-5df34b2083e8@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Matthieu Baerts (NGI0)
2025-01-08 16:34:32 +01:00
committed by Greg Kroah-Hartman
parent c0dde4a52b
commit 3cd0659deb
1 changed files with 2 additions and 1 deletions
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3
net/sctp/sysctl.c
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@@ -380,7 +380,8 @@ static struct ctl_table sctp_net_table[] = {
static int proc_sctp_do_hmac_alg(struct ctl_table *ctl, int write, static int proc_sctp_do_hmac_alg(struct ctl_table *ctl, int write,
void *buffer, size_t *lenp, loff_t *ppos) 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.sctp_hmac_alg);
struct ctl_table tbl; struct ctl_table tbl;
bool changed = false; bool changed = false;
char *none = "none"; char *none = "none";