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smb: client: reject userspace cifs.spnego descriptions #291

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Merged
ixhamza merged 1 commit into from
Jun 9, 2026
Merged

smb: client: reject userspace cifs.spnego descriptions #291

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16 changes: 16 additions & 0 deletions fs/smb/client/cifs_spnego.c
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Original file line number Diff line number Diff line change
Expand Up @@ -8,6 +8,7 @@
*/

#include <linux/list.h>
#include <linux/cred.h>
#include <linux/slab.h>
#include <linux/string.h>
#include <keys/user-type.h>
Expand Down Expand Up @@ -46,12 +47,27 @@ cifs_spnego_key_destroy(struct key *key)
kfree(key->payload.data[0]);
}

static int
cifs_spnego_key_vet_description(const char *description)
{
/*
* cifs.spnego descriptions are authority-bearing inputs to cifs.upcall.
* They are only valid when produced by CIFS while using the private
* spnego_cred installed below. Do not let userspace create this type
* of key through request_key(2)/add_key(2), since the helper treats
* pid/uid/creduid/upcall_target as kernel-originating fields.
*/
if (current_cred() != spnego_cred)
return -EPERM;
return 0;
}

/*
* keytype for CIFS spnego keys
*/
struct key_type cifs_spnego_key_type = {
.name = "cifs.spnego",
.vet_description = cifs_spnego_key_vet_description,
.instantiate = cifs_spnego_key_instantiate,
.destroy = cifs_spnego_key_destroy,
.describe = user_describe,
Expand Down
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