[PATCH v3] KEYS: encrypted: fix integer overflow of datablob_len

[Jarkko Sakkinen]

On Wed, Sep 09, 2026 at 11:34:33AM -0400, Cen Zhang wrote:
> encrypted_key_alloc() stores datablob_len in a u16. It is computed from
> multiple string and payload lengths. If the result exceeds U16_MAX, the
> assignment truncates the allocation size. KASAN reports a 32760-byte
> slab-out-of-bounds write when __ekey_init() copies the master key
> description into the undersized buffer.
> 
> The total payload length stored in key->datalen is also a u16. Use
> check_add_overflow() to reject values that do not fit either destination,
> and use kzalloc_flex() for the flexible-array allocation.
> 
> Fixes: 7e70cb497850 ("keys: add new key-type encrypted")
> Cc: stable at vger.kernel.org
> Link: https://lore.kernel.org/keyrings/20260826154456.85974-1-blbllhy@gmail.com/
> Assisted-by: GitHub-Copilot:claude-opus-4.6
> Signed-off-by: Cen Zhang <cenzhang at linux.microsoft.com>
> Signed-off-by: Francis Perron <francis at akrites.dev>
> ---
> Changes in v3:
> - Describe the bounds using u16 and U16_MAX and simplify the commit
>   message.
> - Include the KASAN-reported write size.
> - Remove organization names from the author and sign-off identities.
> - Remove the unnecessary off-list discussion note.
> - Use cenzhang at linux.microsoft.com.
> - No code changes.
> 
>  security/keys/encrypted-keys/encrypted.c | 20 ++++++++++++++------
>  1 file changed, 14 insertions(+), 6 deletions(-)
> 
> diff --git a/security/keys/encrypted-keys/encrypted.c b/security/keys/encrypted-keys/encrypted.c
> index 59cb77b237b3..e07092ea301a 100644
> --- a/security/keys/encrypted-keys/encrypted.c
> +++ b/security/keys/encrypted-keys/encrypted.c
> @@ -19,6 +19,7 @@
>  #include <linux/parser.h>
>  #include <linux/string.h>
>  #include <linux/err.h>
> +#include <linux/overflow.h>
>  #include <keys/user-type.h>
>  #include <keys/trusted-type.h>
>  #include <keys/encrypted-type.h>
> @@ -579,6 +580,7 @@ static struct encrypted_key_payload *encrypted_key_alloc(struct key *key,
>  {
>  	struct encrypted_key_payload *epayload = NULL;
>  	unsigned short datablob_len;
> +	unsigned short payload_totallen;
>  	unsigned short decrypted_datalen;
>  	unsigned short payload_datalen;
>  	unsigned int encrypted_datalen;
> @@ -632,16 +634,22 @@ static struct encrypted_key_payload *encrypted_key_alloc(struct key *key,
>  
>  	encrypted_datalen = roundup(decrypted_datalen, blksize);
>  
> -	datablob_len = format_len + 1 + strlen(master_desc) + 1
> -	    + strlen(datalen) + 1 + ivsize + 1 + encrypted_datalen;
> +	if (check_add_overflow(format_len + 1 + strlen(master_desc) + 1
> +			       + strlen(datalen) + 1 + ivsize + 1,
> +			       encrypted_datalen, &datablob_len))
> +		return ERR_PTR(-EINVAL);
> +
> +	if (check_add_overflow(datablob_len,
> +			       payload_datalen + HASH_SIZE + 1,
> +			       &payload_totallen))
> +		return ERR_PTR(-EINVAL);
>  
> -	ret = key_payload_reserve(key, payload_datalen + datablob_len
> -				  + HASH_SIZE + 1);
> +	ret = key_payload_reserve(key, payload_totallen);
>  	if (ret < 0)
>  		return ERR_PTR(ret);
>  
> -	epayload = kzalloc(sizeof(*epayload) + payload_datalen +
> -			   datablob_len + HASH_SIZE + 1, GFP_KERNEL);
> +	epayload = kzalloc_flex(*epayload, payload_data, payload_totallen,
> +				GFP_KERNEL);
>  	if (!epayload)
>  		return ERR_PTR(-ENOMEM);
>  
> 
> base-commit: 893e11787f78e43b534e252249ac3fff4d1333f8
> -- 
> 2.55.0

Thanks!

Reviewed-by: Jarkko Sakkinen <jarkko at kernel.org>

BR, Jarkko