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

[Jarkko Sakkinen <jarkko@kernel.org>]

On Thu, Sep 10, 2026 at 10:14:57AM +0530, R Nageswara Sastry wrote:
> 
> On 09.09.2026 9:04 PM, 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@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@linux.microsoft.com>
> > Signed-off-by: Francis Perron <francis@akrites.dev>
> Tested-by: R Nageswara Sastry <rnsastry@linux.ibm.com>
> 
> System: ppc64le LPAR (IBM POWER), Linux 7.3-rc2
> > ---
> > 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@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
> 
> -- 
> Thanks and Regards
> R.Nageswara Sastry
> 


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

BR, Jarkko