HUAWEI TECHNOLOGIES Duesseldorf GmbH, HRB 56063 Managing Director: Li Peng, Li Jian, Shi Yanli
-----Original Message----- From: Mimi Zohar [mailto:zohar@linux.ibm.com] Sent: Wednesday, April 22, 2020 10:56 PM To: Roberto Sassu roberto.sassu@huawei.com Cc: linux-integrity@vger.kernel.org; linux-security-module@vger.kernel.org; linux-kernel@vger.kernel.org; Krzysztof Struczynski krzysztof.struczynski@huawei.com; Silviu Vlasceanu Silviu.Vlasceanu@huawei.com; stable@vger.kernel.org Subject: Re: [PATCH 3/5] ima: Fix ima digest hash table key calculation
Hi Roberto, Krsysztof,
On Wed, 2020-03-25 at 17:11 +0100, Roberto Sassu wrote:
From: Krzysztof Struczynski krzysztof.struczynski@huawei.com
Function hash_long() accepts unsigned long, while currently only one byte is passed from ima_hash_key(), which calculates a key for ima_htable.
Use
more bytes to avoid frequent collisions.
Length of the buffer is not explicitly passed as a function parameter, because this function expects a digest whose length is greater than the size of unsigned long.
Somehow I missed the original report of this problem https://lore.kern el.org/patchwork/patch/674684/. This patch is definitely better, but how many unique keys are actually being used? Is it anywhere near IMA_MEASURE_HTABLE_SIZE(512)?
I did a small test (with 1043 measurements):
slots: 250, max depth: 9 (without the patch) slots: 448, max depth: 7 (with the patch)
Then, I increased the number of bits to 10:
slots: 251, max depth: 9 (without the patch) slots: 660, max depth: 4 (with the patch)
Do we need a new securityfs entry to display the number used?
Probably it is useful only if the administrator can decide the number of slots.
Roberto
HUAWEI TECHNOLOGIES Duesseldorf GmbH, HRB 56063 Managing Director: Li Peng, Li Jian, Shi Yanli
Cc: stable@vger.kernel.org Fixes: 3323eec921ef ("integrity: IMA as an integrity service provider") Signed-off-by: Krzysztof Struczynski krzysztof.struczynski@huawei.com
security/integrity/ima/ima.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h index 64317d95363e..cf0022c2bc14 100644 --- a/security/integrity/ima/ima.h +++ b/security/integrity/ima/ima.h @@ -177,7 +177,7 @@ extern struct ima_h_table ima_htable;
static inline unsigned long ima_hash_key(u8 *digest) {
- return hash_long(*digest, IMA_HASH_BITS);
- return hash_long(*((unsigned long *)digest), IMA_HASH_BITS);
}
#define __ima_hooks(hook) \