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Subject[PATCH 4.9 268/329] ima: Fallback to the builtin hash algorithm
Date
4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Petr Vorel <pvorel@suse.cz>

[ Upstream commit ab60368ab6a452466885ef4edf0cefd089465132 ]

IMA requires having it's hash algorithm be compiled-in due to it's
early use. The default IMA algorithm is protected by Kconfig to be
compiled-in.

The ima_hash kernel parameter allows to choose the hash algorithm. When
the specified algorithm is not available or available as a module, IMA
initialization fails, which leads to a 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@suse.cz>
Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
security/integrity/ima/ima_crypto.c | 2 ++
security/integrity/ima/ima_main.c | 13 +++++++++++++
2 files changed, 15 insertions(+)

--- a/security/integrity/ima/ima_crypto.c
+++ b/security/integrity/ima/ima_crypto.c
@@ -78,6 +78,8 @@ 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;
}

--- 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>
@@ -426,6 +429,16 @@ static int __init init_ima(void)

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();

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