[PATCH][next] ima: ima_modsig: Fix use-after-free bug in ima_read_modsig

[PATCH][next] ima: ima_modsig: Fix use-after-free bug in ima_read_modsig

[Gustavo A. R. Silva]

hdr is being freed and then dereferenced by accessing hdr->pkcs7_msg

Fix this by copying the value returned by PTR_ERR(hdr->pkcs7_msg) into
automatic variable err for its safe use after freeing hdr.

Addresses-Coverity-ID: 1485813 ("Read from pointer after free")
Fixes: 39b07096364a ("ima: Implement support for module-style appended signatures")
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
---
 security/integrity/ima/ima_modsig.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/security/integrity/ima/ima_modsig.c b/security/integrity/ima/ima_modsig.c
index c412e31d1714..e681d4326145 100644
--- a/security/integrity/ima/ima_modsig.c
+++ b/security/integrity/ima/ima_modsig.c
@@ -91,8 +91,9 @@ int ima_read_modsig(enum ima_hooks func, const void *buf, loff_t buf_len,
 
 	hdr->pkcs7_msg = pkcs7_parse_message(buf + buf_len, sig_len);
 	if (IS_ERR(hdr->pkcs7_msg)) {
+		int err = PTR_ERR(hdr->pkcs7_msg);
 		kfree(hdr);
-		return PTR_ERR(hdr->pkcs7_msg);
+		return err;
 	}
 
 	memcpy(hdr->raw_pkcs7, buf + buf_len, sig_len);
-- 
2.22.0

Re: [PATCH][next] ima: ima_modsig: Fix use-after-free bug in ima_read_modsig

[Mimi Zohar]

Hi Gustavo,

On Sun, 2019-08-11 at 18:55 -0500, Gustavo A. R. Silva wrote:
> hdr is being freed and then dereferenced by accessing hdr->pkcs7_msg
> 
> Fix this by copying the value returned by PTR_ERR(hdr->pkcs7_msg) into
> automatic variable err for its safe use after freeing hdr.
> 
> Addresses-Coverity-ID: 1485813 ("Read from pointer after free")
> Fixes: 39b07096364a ("ima: Implement support for module-style appended signatures")
> Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>

This bug was reported Julia and addressed by Thiago on 8/7. If you
would like to add your Review/Tested-by, the patch can be found in the
linux-integrity next-queued-testing branch.

thanks,

Mimi

Re: [PATCH][next] ima: ima_modsig: Fix use-after-free bug in ima_read_modsig

[Gustavo A. R. Silva]

On 8/28/19 8:50 AM, Mimi Zohar wrote:
> Hi Gustavo,
> 
> On Sun, 2019-08-11 at 18:55 -0500, Gustavo A. R. Silva wrote:
>> hdr is being freed and then dereferenced by accessing hdr->pkcs7_msg
>>
>> Fix this by copying the value returned by PTR_ERR(hdr->pkcs7_msg) into
>> automatic variable err for its safe use after freeing hdr.
>>
>> Addresses-Coverity-ID: 1485813 ("Read from pointer after free")
>> Fixes: 39b07096364a ("ima: Implement support for module-style appended signatures")
>> Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
> 
> This bug was reported Julia and addressed by Thiago on 8/7. If you
> would like to add your Review/Tested-by, the patch can be found in the
> linux-integrity next-queued-testing branch.
> 

I'm glad this is fixed now. :)

Yeah, you can add my:

Reviewed-by: Gustavo A. R. Silva <gustavo@embeddedor.com>

Thanks
--
Gustavo