RE: [PATCH v4 04/11] ima: Move ima_reset_appraise_flags() call to post hooks
From: Roberto Sassu <roberto.sassu@huawei.com>
Date: 2021-04-28 15:35:37
Also in:
linux-fsdevel, linux-security-module, lkml
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From: Roberto Sassu Sent: Friday, March 5, 2021 4:19 PM ima_inode_setxattr() and ima_inode_removexattr() hooks are called before an operation is performed. Thus, ima_reset_appraise_flags() should not be called there, as flags might be unnecessarily reset if the operation is denied. This patch introduces the post hooks ima_inode_post_setxattr() and ima_inode_post_removexattr(), and adds the call to ima_reset_appraise_flags() in the new functions. Cc: Casey Schaufler <casey@schaufler-ca.com> Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com> --- fs/xattr.c | 2 ++ include/linux/ima.h | 18 ++++++++++++++++++ security/integrity/ima/ima_appraise.c | 25 ++++++++++++++++++++++--- security/security.c | 1 + 4 files changed, 43 insertions(+), 3 deletions(-)diff --git a/fs/xattr.c b/fs/xattr.c index b3444e06cded..81847f132d26 100644 --- a/fs/xattr.c +++ b/fs/xattr.c@@ -16,6 +16,7 @@ #include <linux/namei.h> #include <linux/security.h> #include <linux/evm.h> +#include <linux/ima.h> #include <linux/syscalls.h> #include <linux/export.h> #include <linux/fsnotify.h>@@ -502,6 +503,7 @@ __vfs_removexattr_locked(struct user_namespace*mnt_userns, if (!error) { fsnotify_xattr(dentry); + ima_inode_post_removexattr(dentry, name); evm_inode_post_removexattr(dentry, name); }diff --git a/include/linux/ima.h b/include/linux/ima.h index 61d5723ec303..5e059da43857 100644 --- a/include/linux/ima.h +++ b/include/linux/ima.h@@ -171,7 +171,13 @@ extern void ima_inode_post_setattr(structuser_namespace *mnt_userns, struct dentry *dentry); extern int ima_inode_setxattr(struct dentry *dentry, const char *xattr_name, const void *xattr_value, size_t xattr_value_len); +extern void ima_inode_post_setxattr(struct dentry *dentry, + const char *xattr_name, + const void *xattr_value, + size_t xattr_value_len); extern int ima_inode_removexattr(struct dentry *dentry, const char *xattr_name); +extern void ima_inode_post_removexattr(struct dentry *dentry, + const char *xattr_name); #else static inline bool is_ima_appraise_enabled(void) {@@ -192,11 +198,23 @@ static inline int ima_inode_setxattr(struct dentry*dentry, return 0; } +static inline void ima_inode_post_setxattr(struct dentry *dentry, + const char *xattr_name, + const void *xattr_value, + size_t xattr_value_len) +{ +} + static inline int ima_inode_removexattr(struct dentry *dentry, const char *xattr_name) { return 0; } + +static inline void ima_inode_post_removexattr(struct dentry *dentry, + const char *xattr_name) +{ +} #endif /* CONFIG_IMA_APPRAISE */ #if defined(CONFIG_IMA_APPRAISE) && defined(CONFIG_INTEGRITY_TRUSTED_KEYRING)diff --git a/security/integrity/ima/ima_appraise.cb/security/integrity/ima/ima_appraise.c index 565e33ff19d0..1f029e4c8d7f 100644--- a/security/integrity/ima/ima_appraise.c +++ b/security/integrity/ima/ima_appraise.c@@ -577,21 +577,40 @@ int ima_inode_setxattr(struct dentry *dentry, constchar *xattr_name, if (result == 1) { if (!xattr_value_len || (xvalue->type >= IMA_XATTR_LAST)) return -EINVAL; - ima_reset_appraise_flags(d_backing_inode(dentry), - xvalue->type == EVM_IMA_XATTR_DIGSIG); result = 0; } return result; } +void ima_inode_post_setxattr(struct dentry *dentry, const char *xattr_name, + const void *xattr_value, size_t xattr_value_len) +{ + const struct evm_ima_xattr_data *xvalue = xattr_value; + int result; + + result = ima_protect_xattr(dentry, xattr_name, xattr_value, + xattr_value_len); + if (result == 1) + ima_reset_appraise_flags(d_backing_inode(dentry),
I found an issue in this patch. Moving ima_reset_appraise_flags() to the post hook causes this function to be executed also when __vfs_setxattr_noperm() is called. The problem is that at the end of a write IMA calls ima_collect_measurement() to recalculate the file digest and update security.ima. ima_collect_measurement() sets IMA_COLLECTED. However, after that __vfs_setxattr_noperm() causes IMA_COLLECTED to be reset, and to unnecessarily recalculate the file digest. This wouldn't happen if ima_reset_appraise_flags() is in the pre hook. I solved by replacing: iint->flags &= ~IMA_DONE_MASK; with: iint->flags &= ~(IMA_DONE_MASK & ~IMA_COLLECTED); just when the IMA_CHANGE_XATTR bit is set. It should not be a problem since setting an xattr does not influence the file content. Mimi, what do you think? Thanks Roberto HUAWEI TECHNOLOGIES Duesseldorf GmbH, HRB 56063 Managing Director: Li Peng, Li Jian, Shi Yanli
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+ xvalue->type == EVM_IMA_XATTR_DIGSIG); +} + int ima_inode_removexattr(struct dentry *dentry, const char *xattr_name) { int result; result = ima_protect_xattr(dentry, xattr_name, NULL, 0); if (result == 1) { - ima_reset_appraise_flags(d_backing_inode(dentry), 0); result = 0; } return result; } + +void ima_inode_post_removexattr(struct dentry *dentry, const char *xattr_name) +{ + int result; + + result = ima_protect_xattr(dentry, xattr_name, NULL, 0); + if (result == 1) + ima_reset_appraise_flags(d_backing_inode(dentry), 0); +}diff --git a/security/security.c b/security/security.c index 5ac96b16f8fa..efb1f874dc41 100644 --- a/security/security.c +++ b/security/security.c@@ -1319,6 +1319,7 @@ void security_inode_post_setxattr(struct dentry*dentry, const char *name, if (unlikely(IS_PRIVATE(d_backing_inode(dentry)))) return; call_void_hook(inode_post_setxattr, dentry, name, value, size, flags); + ima_inode_post_setxattr(dentry, name, value, size); evm_inode_post_setxattr(dentry, name, value, size); } -- 2.26.2