[PATCH -next,v2] ima: add cond_resched() in ima_calc_file_hash_tfm loop

[Gaosheng Cui]

When hashing large files, the while loop in ima_calc_file_hash_tfm
processes PAGE_SIZE chunks without any scheduling point, which can
cause soft lockup warnings:
watchdog: BUG: soft lockup - CPU#0 stuck for 50s!
Call Trace:
  _sha256_update+0x12d/0x1a0
  ima_calc_file_hash_tfm+0xfb/0x150
  ima_calc_file_hash+0x6e/0x160
  ima_collect_measurement+0x202/0x340
  process_measurement+0x3a9/0xb30
  ima_file_check+0x56/0xa0
  do_open+0x11b/0x250
  path_openat+0x10b/0x1d0
  do_filp_open+0xa9/0x150
  do_sys_openat2+0x223/0x2a0
  __x64_sys_openat+0x54/0xa0
  do_syscall_64+0x59/0x110
  entry_SYSCALL_64_after_hwframe+0x78/0xe2

Call cond_resched() every 4MB to yield the CPU when needed, rather
than at every loop iteration, to reduce overhead.

Fixes: 3323eec921ef ("integrity: IMA as an integrity service provider")
Signed-off-by: Gaosheng Cui <cuigaoshe...@huawei.com>
---
v2: call cond_resched() every 4MB to yield the CPU when needed
 security/integrity/ima/ima_crypto.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/security/integrity/ima/ima_crypto.c 
b/security/integrity/ima/ima_crypto.c
index 0d72b48249ee..aab2349c0c33 100644
--- a/security/integrity/ima/ima_crypto.c
+++ b/security/integrity/ima/ima_crypto.c
@@ -233,6 +233,9 @@ static int ima_calc_file_hash_tfm(struct file *file,
                rc = crypto_shash_update(shash, rbuf, rbuf_len);
                if (rc)
                        break;
+
+               if (IS_ALIGNED(offset, SZ_4M))
+                       cond_resched();
        }
        kfree(rbuf);
 out:
-- 
2.43.0