On 24/10/14 17:18, Mimi Zohar wrote: > On Fri, 2014-10-24 at 10:07 +0300, Dmitry Kasatkin wrote: >> ima_inode_setxattr() can be called with no value. Function does not >> check the length so that following command can be used to produce >> kernel oops: setfattr -n security.ima FOO. This patch fixes it. >> >> Changes in v2: >> * testing validity of xattr type >> * allow setting hash only in fix or log mode (Mimi) > I only mentioned "fix" mode, not "log" mode (explanation below). >
We need it in log mode as well (explanation bellow) >> [ 261.562522] BUG: unable to handle kernel NULL pointer dereference at >> (null) >> [ 261.564109] IP: [<ffffffff812af272>] ima_inode_setxattr+0x3e/0x5a >> [ 261.564109] PGD 3112f067 PUD 42965067 PMD 0 >> [ 261.564109] Oops: 0000 [#1] SMP >> [ 261.564109] Modules linked in: bridge stp llc evdev serio_raw i2c_piix4 >> button fuse >> [ 261.564109] CPU: 0 PID: 3299 Comm: setxattr Not tainted 3.16.0-kds+ #2924 >> [ 261.564109] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011 >> [ 261.564109] task: ffff8800428c2430 ti: ffff880042be0000 task.ti: >> ffff880042be0000 >> [ 261.564109] RIP: 0010:[<ffffffff812af272>] [<ffffffff812af272>] >> ima_inode_setxattr+0x3e/0x5a >> [ 261.564109] RSP: 0018:ffff880042be3d50 EFLAGS: 00010246 >> [ 261.564109] RAX: 0000000000000001 RBX: 0000000000000000 RCX: >> 0000000000000015 >> [ 261.564109] RDX: 0000001500000000 RSI: 0000000000000000 RDI: >> ffff8800375cc600 >> [ 261.564109] RBP: ffff880042be3d68 R08: 0000000000000000 R09: >> 00000000004d6256 >> [ 261.564109] R10: 0000000000000000 R11: 0000000000000000 R12: >> ffff88002149ba00 >> [ 261.564109] R13: 0000000000000000 R14: 0000000000000000 R15: >> 0000000000000000 >> [ 261.564109] FS: 00007f6c1e219740(0000) GS:ffff88005da00000(0000) >> knlGS:0000000000000000 >> [ 261.564109] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 >> [ 261.564109] CR2: 0000000000000000 CR3: 000000003b35a000 CR4: >> 00000000000006f0 >> [ 261.564109] Stack: >> [ 261.564109] ffff88002149ba00 ffff880042be3df8 0000000000000000 >> ffff880042be3d98 >> [ 261.564109] ffffffff812a101b ffff88002149ba00 ffff880042be3df8 >> 0000000000000000 >> [ 261.564109] 0000000000000000 ffff880042be3de0 ffffffff8116d08a >> ffff880042be3dc8 >> [ 261.564109] Call Trace: >> [ 261.564109] [<ffffffff812a101b>] security_inode_setxattr+0x48/0x6a >> [ 261.564109] [<ffffffff8116d08a>] vfs_setxattr+0x6b/0x9f >> [ 261.564109] [<ffffffff8116d1e0>] setxattr+0x122/0x16c >> [ 261.564109] [<ffffffff811687e8>] ? mnt_want_write+0x21/0x45 >> [ 261.564109] [<ffffffff8114d011>] ? __sb_start_write+0x10f/0x143 >> [ 261.564109] [<ffffffff811687e8>] ? mnt_want_write+0x21/0x45 >> [ 261.564109] [<ffffffff811687c0>] ? __mnt_want_write+0x48/0x4f >> [ 261.564109] [<ffffffff8116d3e6>] SyS_setxattr+0x6e/0xb0 >> [ 261.564109] [<ffffffff81529da9>] system_call_fastpath+0x16/0x1b >> [ 261.564109] Code: 48 89 f7 48 c7 c6 58 36 81 81 53 31 db e8 73 27 04 00 >> 85 c0 75 28 bf 15 00 00 00 e8 8a a5 d9 ff 84 c0 75 05 83 cb ff eb 15 31 f6 >> <41> 80 7d 00 03 49 8b 7c 24 68 40 0f 94 c6 e8 e1 f9 ff ff 89 d8 >> [ 261.564109] RIP [<ffffffff812af272>] ima_inode_setxattr+0x3e/0x5a >> [ 261.564109] RSP <ffff880042be3d50> >> [ 261.564109] CR2: 0000000000000000 >> [ 261.599998] ---[ end trace 39a89a3fc267e652 ]--- >> >> Reported-by: Jan Kara <[email protected]> >> Signed-off-by: Dmitry Kasatkin <[email protected]> >> --- >> security/integrity/ima/ima_appraise.c | 13 +++++++++++-- >> 1 file changed, 11 insertions(+), 2 deletions(-) >> >> diff --git a/security/integrity/ima/ima_appraise.c >> b/security/integrity/ima/ima_appraise.c >> index 9226854..e302cbf 100644 >> --- a/security/integrity/ima/ima_appraise.c >> +++ b/security/integrity/ima/ima_appraise.c >> @@ -378,8 +378,17 @@ int ima_inode_setxattr(struct dentry *dentry, const >> char *xattr_name, >> result = ima_protect_xattr(dentry, xattr_name, xattr_value, >> xattr_value_len); >> if (result == 1) { >> - ima_reset_appraise_flags(dentry->d_inode, >> - (xvalue->type == EVM_IMA_XATTR_DIGSIG) ? 1 : 0); >> + bool digsig; >> + >> + if (!xattr_value_len || >> + (xvalue->type != IMA_XATTR_DIGEST && >> + xvalue->type != IMA_XATTR_DIGEST_NG && >> + xvalue->type != EVM_IMA_XATTR_DIGSIG)) > "xvalue->type" is an enumerated type. Testing each possible value seems > kind of a brittle method for vetting the value. I suggest testing the > existing last value or, better yet, define a last value, so if someone > adds or changes the order, nothing breaks. I was considering to define _LAST value, but we have EVM_XATTR_HMAC in the middle... In fact I was expecting to get some feedback about it, because in reality it is just a sanity check. It does not prevent DoS because it is possible to set correctly formatted but wrong value and force DoS. > >> + return -EINVAL; >> + digsig = (xvalue->type == EVM_IMA_XATTR_DIGSIG); >> + if (!digsig && (ima_appraise & IMA_APPRAISE_ENFORCE)) >> + return -EPERM; > According to the new ima_appraise "log" mode, commit "2faa6ef ima: > provide 'ima_appraise=log' kernel option", "log" mode permits normal > execution without "fixing" anything. Normal execution, here, prevents > writing the extended attribute. 'log' mode is also special mode for system developing and debugging. It is beneficial to be able to 'label' target object with correct value... - Dmitry > Mimi > >> + ima_reset_appraise_flags(dentry->d_inode, digsig); >> result = 0; >> } >> return result; > > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
