IMA requires have it's hash algorithm to be compiled-in due it's early
use. Default IMA algorithm is protected by Kconfig to be compiled-in.
ima_hash kernel parameter allows to choose hash algorithm. When
specified algorithm not available or available as module, IMA
initialization fails, which leads to kernel panic (mknodat syscall calls
ima_post_path_mknod()). Therefore as fallback we force IMA to use
the default builtin Kconfig hash algorithm.
Fixed crash:
$ grep CONFIG_CRYPTO_MD4 .config
CONFIG_CRYPTO_MD4=m
[ 0.000000] Command line: BOOT_IMAGE=/boot/vmlinuz-4.12.14-2.3-default root=UUID=74ae8202-9ca7-4e39-813b-22287ec52f7a video=1024x768-16 plymouth.ignore-serial-consoles console=ttyS0 console=tty resume=/dev/disk/by-path/pci-0000:00:07.0-part3 splash=silent showopts ima_hash=md4
...
[ 1.545190] ima: Can not allocate md4 (reason: -2)
...
[ 2.610120] BUG: unable to handle kernel NULL pointer dereference at (null)
[ 2.611903] IP: ima_match_policy+0x23/0x390
[ 2.612967] PGD 0 P4D 0
[ 2.613080] Oops: 0000 [#1] SMP
[ 2.613080] Modules linked in: autofs4
[ 2.613080] Supported: Yes
[ 2.613080] CPU: 0 PID: 1 Comm: systemd Not tainted 4.12.14-2.3-default #1
[ 2.613080] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.0.0-prebuilt.qemu-project.org 04/01/2014
[ 2.613080] task: ffff88003e2d0040 task.stack: ffffc90000190000
[ 2.613080] RIP: 0010:ima_match_policy+0x23/0x390
[ 2.613080] RSP: 0018:ffffc90000193e88 EFLAGS: 00010296
[ 2.613080] RAX: 0000000000000000 RBX: 000000000000000c RCX: 0000000000000004
[ 2.613080] RDX: 0000000000000010 RSI: 0000000000000001 RDI: ffff880037071728
[ 2.613080] RBP: 0000000000008000 R08: 0000000000000000 R09: 0000000000000000
[ 2.613080] R10: 0000000000000008 R11: 61c8864680b583eb R12: 00005580ff10086f
[ 2.613080] R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000008000
[ 2.613080] FS: 00007f5c1da08940(0000) GS:ffff88003fc00000(0000) knlGS:0000000000000000
[ 2.613080] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 2.613080] CR2: 0000000000000000 CR3: 0000000037002000 CR4: 00000000003406f0
[ 2.613080] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 2.613080] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 2.613080] Call Trace:
[ 2.613080] ? shmem_mknod+0xbf/0xd0
[ 2.613080] ima_post_path_mknod+0x1c/0x40
[ 2.613080] SyS_mknod+0x210/0x220
[ 2.613080] entry_SYSCALL_64_fastpath+0x1a/0xa5
[ 2.613080] RIP: 0033:0x7f5c1bfde570
[ 2.613080] RSP: 002b:00007ffde1c90dc8 EFLAGS: 00000246 ORIG_RAX: 0000000000000085
[ 2.613080] RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f5c1bfde570
[ 2.613080] RDX: 0000000000000000 RSI: 0000000000008000 RDI: 00005580ff10086f
[ 2.613080] RBP: 00007ffde1c91040 R08: 00005580ff10086f R09: 0000000000000000
[ 2.613080] R10: 0000000000104000 R11: 0000000000000246 R12: 00005580ffb99660
[ 2.613080] R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000002
[ 2.613080] Code: 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 41 57 41 56 44 8d 14 09 41 55 41 54 55 53 44 89 d3 09 cb 48 83 ec 38 48 8b 05 c5 03 29 01 <4c> 8b 20 4c 39 e0 0f 84 d7 01 00 00 4c 89 44 24 08 89 54 24 20
[ 2.613080] RIP: ima_match_policy+0x23/0x390 RSP: ffffc90000193e88
[ 2.613080] CR2: 0000000000000000
[ 2.613080] ---[ end trace 9a9f0a8a73079f6a ]---
[ 2.673052] Kernel panic - not syncing: Attempted to kill init! exitcode=0x00000009
[ 2.673052]
[ 2.675337] Kernel Offset: disabled
[ 2.676405] ---[ end Kernel panic - not syncing: Attempted to kill init! exitcode=0x00000009
Signed-off-by: Petr Vorel <pvorel@xxxxxxx>
---
Changes v2->v3:
* Return back to v1 variant + log in ima_init_crypto() and in
init_ima().
I choose not to detect and mention in ima_init_crypto() whether
allocated hash is default or not (I don't consider it important enough
if everything work well and don't want to say "default" when some of
working algorithms actually aren't default, e.g. md5).
But I decide to put this info in init_ima() in case we load default
algorithm as fallback.
$ grep -e ^CONFIG_IMA_DEFAULT_HASH -e CONFIG_CRYPTO_MD[45] .config
CONFIG_IMA_DEFAULT_HASH_SHA256=y
CONFIG_IMA_DEFAULT_HASH="sha256"
CONFIG_CRYPTO_MD4=m
CONFIG_CRYPTO_MD5=y
* default (none) or ima_hash=sha256
[ 2.162025] ima: Allocated hash algorithm: sha256
* ima_hash=md4
[ 2.136885] ima: Can not allocate md4 (reason: -2)
[ 2.138364] ima: Allocating md4 failed, going to use default hash algorithm sha256
[ 2.141472] ima: Allocated hash algorithm: sha256
* ima_hash=md5
[ 2.128360] ima: Allocated hash algorithm: md5
---
security/integrity/ima/ima_crypto.c | 2 ++
security/integrity/ima/ima_main.c | 13 +++++++++++++
2 files changed, 15 insertions(+)
diff --git a/security/integrity/ima/ima_crypto.c b/security/integrity/ima/ima_crypto.c
index 205bc69361ea..4e085a17124f 100644
--- a/security/integrity/ima/ima_crypto.c
+++ b/security/integrity/ima/ima_crypto.c
@@ -73,6 +73,8 @@ int __init ima_init_crypto(void)
hash_algo_name[ima_hash_algo], rc);
return rc;
}
+ pr_info("Allocated hash algorithm: %s\n",
+ hash_algo_name[ima_hash_algo]);
return 0;
}
diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
index 5d122daf5c8a..74d0bd7e76d7 100644
--- a/security/integrity/ima/ima_main.c
+++ b/security/integrity/ima/ima_main.c
@@ -16,6 +16,9 @@
* implements the IMA hooks: ima_bprm_check, ima_file_mmap,
* and ima_file_check.
*/
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
#include <linux/module.h>
#include <linux/file.h>
#include <linux/binfmts.h>
@@ -504,6 +507,16 @@ static int __init init_ima(void)
ima_init_template_list();
hash_setup(CONFIG_IMA_DEFAULT_HASH);
error = ima_init();
+
+ if (error && strcmp(hash_algo_name[ima_hash_algo],
+ CONFIG_IMA_DEFAULT_HASH) != 0) {
+ pr_info("Allocating %s failed, going to use default hash algorithm %s\n",
+ hash_algo_name[ima_hash_algo], CONFIG_IMA_DEFAULT_HASH);
+ hash_setup_done = 0;
+ hash_setup(CONFIG_IMA_DEFAULT_HASH);
+ error = ima_init();
+ }
+
if (!error) {
ima_initialized = 1;
ima_update_policy_flag();
--
2.12.3
