| Message ID | 20200409033907.102833-1-tianjia.zhang@linux.alibaba.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | support to read and tune appraise mode in runtime | expand |
On Thu, 2020-04-09 at 11:39 +0800, Tianjia Zhang wrote: > Support the read and write operations of ima_appraise by adding a > securifyfs file 'appraise_mode'. > > In order to tune appraise mode in runtime, writing a PKCS#7 signature > corresponding the signed content is required. The content should be off, > enforce, log or fix. Given a simple way to archive this: > > $ echo -n off > mode > $ openssl smime -sign -nocerts -noattr -binary \ > -in mode -inkey <system_trusted_key> \ > -signer <cert> -outform der -out mode.p7s > $ sudo cat mode.p7s \ > > /sys/kernel/security/ima/appraise_mode > > Note that the signing key must be a trust key located in > system trusted keyring. So even the root privilege cannot > simply disable the enforcement. There are major problems with disabling IMA appraisal. This patch set proposes disabling IMA appraisal without even providing the motivation for such support. A lot of effort went into preventing custom IMA policies from disabling appraising the kexec or kernel module signatures. In addition, the "lockdown" patch set was upstreamed permitting IMA signature verification. This patch set would break both of these features. IMA relies on its own keyring for verifying file signatures, not the builtin or secondary trusted kernel keyrings. Two methods already exist - xattr and appended signatures - for verifying file signatures. This patch set assumes creating and signing a file, which is then written to a securityfs file. Like for loading a custom IMA policy, instead of cat'ing the file, write the pathname to the securityfs file. If you must define a new IMA method for verifying file signatures, then it needs to be generic and added to ima_appraise_measurement(). (Refer to the new IMA appended signature support.) Mimi > > Tianjia Zhang (2): > ima: support to read appraise mode > ima: support to tune appraise mode in runtime > > security/integrity/ima/ima_fs.c | 134 +++++++++++++++++++++++++++++++- > 1 file changed, 133 insertions(+), 1 deletion(-) >
On 2020/4/14 5:55, Mimi Zohar wrote: > On Thu, 2020-04-09 at 11:39 +0800, Tianjia Zhang wrote: >> Support the read and write operations of ima_appraise by adding a >> securifyfs file 'appraise_mode'. >> >> In order to tune appraise mode in runtime, writing a PKCS#7 signature >> corresponding the signed content is required. The content should be off, >> enforce, log or fix. Given a simple way to archive this: >> >> $ echo -n off > mode >> $ openssl smime -sign -nocerts -noattr -binary \ >> -in mode -inkey <system_trusted_key> \ >> -signer <cert> -outform der -out mode.p7s >> $ sudo cat mode.p7s \ >> > /sys/kernel/security/ima/appraise_mode >> >> Note that the signing key must be a trust key located in >> system trusted keyring. So even the root privilege cannot >> simply disable the enforcement. > > There are major problems with disabling IMA appraisal. This patch set > proposes disabling IMA appraisal without even providing the motivation > for such support. > > A lot of effort went into preventing custom IMA policies from > disabling appraising the kexec or kernel module signatures. In > addition, the "lockdown" patch set was upstreamed permitting IMA > signature verification. This patch set would break both of these > features. > > IMA relies on its own keyring for verifying file signatures, not the > builtin or secondary trusted kernel keyrings. > > Two methods already exist - xattr and appended signatures - for > verifying file signatures. This patch set assumes creating and > signing a file, which is then written to a securityfs file. Like for > loading a custom IMA policy, instead of cat'ing the file, write the > pathname to the securityfs file. > > If you must define a new IMA method for verifying file signatures, > then it needs to be generic and added to ima_appraise_measurement(). > (Refer to the new IMA appended signature support.) > > Mimi > >> >> Tianjia Zhang (2): >> ima: support to read appraise mode >> ima: support to tune appraise mode in runtime >> >> security/integrity/ima/ima_fs.c | 134 +++++++++++++++++++++++++++++++- >> 1 file changed, 133 insertions(+), 1 deletion(-) >> Thanks for your suggestion, the way to close the appraise mode here is indeed a bit rude, I will reconsider again according to your suggestions. In addition, [PATCH 1/2] ima: support to read appraise mode, by the way, see if this patch is acceptable. Thanks and best, Tianjia
On Tue, 2020-04-14 at 11:36 +0800, Tianjia Zhang wrote: > > On 2020/4/14 5:55, Mimi Zohar wrote: > > On Thu, 2020-04-09 at 11:39 +0800, Tianjia Zhang wrote: > >> Support the read and write operations of ima_appraise by adding a > >> securifyfs file 'appraise_mode'. > >> > >> In order to tune appraise mode in runtime, writing a PKCS#7 signature > >> corresponding the signed content is required. The content should be off, > >> enforce, log or fix. Given a simple way to archive this: > >> > >> $ echo -n off > mode > >> $ openssl smime -sign -nocerts -noattr -binary \ > >> -in mode -inkey <system_trusted_key> \ > >> -signer <cert> -outform der -out mode.p7s > >> $ sudo cat mode.p7s \ > >> > /sys/kernel/security/ima/appraise_mode > >> > >> Note that the signing key must be a trust key located in > >> system trusted keyring. So even the root privilege cannot > >> simply disable the enforcement. > > > > There are major problems with disabling IMA appraisal. This patch set > > proposes disabling IMA appraisal without even providing the motivation > > for such support. > > > > A lot of effort went into preventing custom IMA policies from > > disabling appraising the kexec or kernel module signatures. In > > addition, the "lockdown" patch set was upstreamed permitting IMA > > signature verification. This patch set would break both of these > > features. > > > > IMA relies on its own keyring for verifying file signatures, not the > > builtin or secondary trusted kernel keyrings. > > > > Two methods already exist - xattr and appended signatures - for > > verifying file signatures. This patch set assumes creating and > > signing a file, which is then written to a securityfs file. Like for > > loading a custom IMA policy, instead of cat'ing the file, write the > > pathname to the securityfs file. > > > > If you must define a new IMA method for verifying file signatures, > > then it needs to be generic and added to ima_appraise_measurement(). > > (Refer to the new IMA appended signature support.) > > > > Mimi > > > >> > >> Tianjia Zhang (2): > >> ima: support to read appraise mode > >> ima: support to tune appraise mode in runtime > >> > >> security/integrity/ima/ima_fs.c | 134 +++++++++++++++++++++++++++++++- > >> 1 file changed, 133 insertions(+), 1 deletion(-) > >> > > Thanks for your suggestion, the way to close the appraise mode here is > indeed a bit rude, I will reconsider again according to your suggestions. > > In addition, [PATCH 1/2] ima: support to read appraise mode, by the way, > see if this patch is acceptable. My comments were not meant as suggestions, but as an explanation as to how IMA works. More details follow. IMA is based on policy. That decision was made a long time ago. It allowed distros to configure IMA, allowing customers to experiment with it. You have one opportunity to totally change the boot time policy rules, by loading a custom policy. After that, rules may only be added. There is no valid reason for "turning off" the policy once it has been enabled. It breaks existing expectations. Mimi
On 2020/4/14 21:41, Mimi Zohar wrote: > On Tue, 2020-04-14 at 11:36 +0800, Tianjia Zhang wrote: >> >> On 2020/4/14 5:55, Mimi Zohar wrote: >>> On Thu, 2020-04-09 at 11:39 +0800, Tianjia Zhang wrote: >>>> Support the read and write operations of ima_appraise by adding a >>>> securifyfs file 'appraise_mode'. >>>> >>>> In order to tune appraise mode in runtime, writing a PKCS#7 signature >>>> corresponding the signed content is required. The content should be off, >>>> enforce, log or fix. Given a simple way to archive this: >>>> >>>> $ echo -n off > mode >>>> $ openssl smime -sign -nocerts -noattr -binary \ >>>> -in mode -inkey <system_trusted_key> \ >>>> -signer <cert> -outform der -out mode.p7s >>>> $ sudo cat mode.p7s \ >>>> > /sys/kernel/security/ima/appraise_mode >>>> >>>> Note that the signing key must be a trust key located in >>>> system trusted keyring. So even the root privilege cannot >>>> simply disable the enforcement. >>> >>> There are major problems with disabling IMA appraisal. This patch set >>> proposes disabling IMA appraisal without even providing the motivation >>> for such support. >>> >>> A lot of effort went into preventing custom IMA policies from >>> disabling appraising the kexec or kernel module signatures. In >>> addition, the "lockdown" patch set was upstreamed permitting IMA >>> signature verification. This patch set would break both of these >>> features. >>> >>> IMA relies on its own keyring for verifying file signatures, not the >>> builtin or secondary trusted kernel keyrings. >>> >>> Two methods already exist - xattr and appended signatures - for >>> verifying file signatures. This patch set assumes creating and >>> signing a file, which is then written to a securityfs file. Like for >>> loading a custom IMA policy, instead of cat'ing the file, write the >>> pathname to the securityfs file. >>> >>> If you must define a new IMA method for verifying file signatures, >>> then it needs to be generic and added to ima_appraise_measurement(). >>> (Refer to the new IMA appended signature support.) >>> >>> Mimi >>> >>>> >>>> Tianjia Zhang (2): >>>> ima: support to read appraise mode >>>> ima: support to tune appraise mode in runtime >>>> >>>> security/integrity/ima/ima_fs.c | 134 +++++++++++++++++++++++++++++++- >>>> 1 file changed, 133 insertions(+), 1 deletion(-) >>>> >> >> Thanks for your suggestion, the way to close the appraise mode here is >> indeed a bit rude, I will reconsider again according to your suggestions. >> >> In addition, [PATCH 1/2] ima: support to read appraise mode, by the way, >> see if this patch is acceptable. > > My comments were not meant as suggestions, but as an explanation as to > how IMA works. More details follow. > > IMA is based on policy. That decision was made a long time ago. It > allowed distros to configure IMA, allowing customers to experiment > with it. You have one opportunity to totally change the boot time > policy rules, by loading a custom policy. After that, rules may only > be added. > > There is no valid reason for "turning off" the policy once it has been > enabled. It breaks existing expectations. > > Mimi > Thank you very much for your explanation. I'm sorry I may not have stated clearly. I didn't have to change the working mode of IMA. I was convinced by you to give up the idea of "turn off" the appraise. However, it should be possible to support appraise mode reading. Right?
Support the read and write operations of ima_appraise by adding a securifyfs file 'appraise_mode'. In order to tune appraise mode in runtime, writing a PKCS#7 signature corresponding the signed content is required. The content should be off, enforce, log or fix. Given a simple way to archive this: $ echo -n off > mode $ openssl smime -sign -nocerts -noattr -binary \ -in mode -inkey <system_trusted_key> \ -signer <cert> -outform der -out mode.p7s $ sudo cat mode.p7s \ > /sys/kernel/security/ima/appraise_mode Note that the signing key must be a trust key located in system trusted keyring. So even the root privilege cannot simply disable the enforcement. Tianjia Zhang (2): ima: support to read appraise mode ima: support to tune appraise mode in runtime security/integrity/ima/ima_fs.c | 134 +++++++++++++++++++++++++++++++- 1 file changed, 133 insertions(+), 1 deletion(-)