Messages in this thread | | | Date | Sat, 10 Jun 2023 09:09:51 +0200 | Subject | Re: [PATCH v11 2/4] smack: Set the SMACK64TRANSMUTE xattr in smack_inode_init_security() | From | Roberto Sassu <> |
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On 6/9/2023 9:35 PM, Mimi Zohar wrote: > Hi Roberto, > > On Sat, 2023-06-03 at 21:15 +0200, Roberto Sassu wrote: >> From: Roberto Sassu <roberto.sassu@huawei.com> >> >> With the newly added ability of LSMs to supply multiple xattrs, set >> SMACK64TRASMUTE in smack_inode_init_security(), instead of d_instantiate(). >> Do it by incrementing SMACK_INODE_INIT_XATTRS to 2 and by calling >> lsm_get_xattr_slot() a second time, if the transmuting conditions are met. >> >> The LSM infrastructure passes all xattrs provided by LSMs to the >> filesystems through the initxattrs() callback, so that filesystems can >> store xattrs in the disk. >> >> After the change, the SMK_INODE_TRANSMUTE inode flag is always set by >> d_instantiate() after fetching SMACK64TRANSMUTE from the disk. Before it >> was done by smack_inode_post_setxattr() as result of the __vfs_setxattr() >> call. >> >> Removing __vfs_setxattr() also prevents invalidating the EVM HMAC, by >> adding a new xattr without checking and updating the existing HMAC. >> >> Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com> > > Just a few comments/nits inline. > >> --- >> security/smack/smack.h | 2 +- >> security/smack/smack_lsm.c | 43 +++++++++++++++++++++++--------------- >> 2 files changed, 27 insertions(+), 18 deletions(-) >> >> diff --git a/security/smack/smack.h b/security/smack/smack.h >> index aa15ff56ed6..041688e5a77 100644 >> --- a/security/smack/smack.h >> +++ b/security/smack/smack.h >> @@ -128,7 +128,7 @@ struct task_smack { >> >> #define SMK_INODE_INSTANT 0x01 /* inode is instantiated */ >> #define SMK_INODE_TRANSMUTE 0x02 /* directory is transmuting */ >> -#define SMK_INODE_CHANGED 0x04 /* smack was transmuted */ >> +#define SMK_INODE_CHANGED 0x04 /* smack was transmuted (unused) */ >> #define SMK_INODE_IMPURE 0x08 /* involved in an impure transaction */ >> >> /* >> diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c >> index a1c30275692..b67d901ee74 100644 >> --- a/security/smack/smack_lsm.c >> +++ b/security/smack/smack_lsm.c >> @@ -52,7 +52,14 @@ >> #define SMK_RECEIVING 1 >> #define SMK_SENDING 2 >> >> -#define SMACK_INODE_INIT_XATTRS 1 >> +/* >> + * Smack uses multiple xattrs. >> + * SMACK64 - for access control, >> + * SMACK64TRANSMUTE - label initialization, >> + * Not saved on files - SMACK64IPIN and SMACK64IPOUT, >> + * Must be set explicitly - SMACK64EXEC and SMACK64MMAP >> + */ >> +#define SMACK_INODE_INIT_XATTRS 2 >> >> #ifdef SMACK_IPV6_PORT_LABELING >> static DEFINE_MUTEX(smack_ipv6_lock); >> @@ -935,7 +942,6 @@ static int smack_inode_init_security(struct inode *inode, struct inode *dir, >> struct xattr *xattrs, int *xattr_count) >> { >> struct task_smack *tsp = smack_cred(current_cred()); >> - struct inode_smack *issp = smack_inode(inode); >> struct smack_known *skp = smk_of_task(tsp); >> struct smack_known *isp = smk_of_inode(inode); >> struct smack_known *dsp = smk_of_inode(dir); >> @@ -963,6 +969,8 @@ static int smack_inode_init_security(struct inode *inode, struct inode *dir, >> if ((tsp->smk_task == tsp->smk_transmuted) || >> (may > 0 && ((may & MAY_TRANSMUTE) != 0) && >> smk_inode_transmutable(dir))) { >> + struct xattr *xattr_transmute; >> + > > Variables should be defined at the beginning of the function.
Casey asked to declare the variable in this block.
> Is there a reason for beginning the function with "if (xattr) {" > instead "if (!xattr) return 0;". This causes unnecessary indenting.
I revisited this part and made few fixes:
https://lore.kernel.org/linux-security-module/20230607123612.2791303-1-roberto.sassu@huaweicloud.com/
Patch 3 should address your concern.
>> /* >> * The caller of smack_dentry_create_files_as() >> * should have overridden the current cred, so the >> @@ -971,7 +979,16 @@ static int smack_inode_init_security(struct inode *inode, struct inode *dir, >> */ >> if (tsp->smk_task != tsp->smk_transmuted) >> isp = dsp; >> - issp->smk_flags |= SMK_INODE_CHANGED; >> + xattr_transmute = lsm_get_xattr_slot(xattrs, xattr_count); >> + if (xattr_transmute) { >> + xattr_transmute->value = kmemdup(TRANS_TRUE, >> + TRANS_TRUE_SIZE, GFP_NOFS); > > script/checkpatch --strict complains here.
Thanks, I didn't know about it.
It seems that they are more stylistic things. Probably, not worth to respin the patch set just for those (unless you prefer I do it).
Thanks
Roberto
>> + if (xattr_transmute->value == NULL) >> + return -ENOMEM; >> + >> + xattr_transmute->value_len = TRANS_TRUE_SIZE; >> + xattr_transmute->name = XATTR_SMACK_TRANSMUTE; >> + } >> } >> >> xattr->value = kstrdup(isp->smk_known, GFP_NOFS); >> @@ -3518,20 +3535,12 @@ static void smack_d_instantiate(struct dentry *opt_dentry, struct inode *inode) >> * If there is a transmute attribute on the >> * directory mark the inode. >> */ >> - if (isp->smk_flags & SMK_INODE_CHANGED) { >> - isp->smk_flags &= ~SMK_INODE_CHANGED; >> - rc = __vfs_setxattr(&nop_mnt_idmap, dp, inode, >> - XATTR_NAME_SMACKTRANSMUTE, >> - TRANS_TRUE, TRANS_TRUE_SIZE, >> - 0); >> - } else { >> - rc = __vfs_getxattr(dp, inode, >> - XATTR_NAME_SMACKTRANSMUTE, trattr, >> - TRANS_TRUE_SIZE); >> - if (rc >= 0 && strncmp(trattr, TRANS_TRUE, >> - TRANS_TRUE_SIZE) != 0) >> - rc = -EINVAL; >> - } >> + rc = __vfs_getxattr(dp, inode, >> + XATTR_NAME_SMACKTRANSMUTE, trattr, >> + TRANS_TRUE_SIZE); >> + if (rc >= 0 && strncmp(trattr, TRANS_TRUE, >> + TRANS_TRUE_SIZE) != 0) >> + rc = -EINVAL; >> if (rc >= 0) >> transflag = SMK_INODE_TRANSMUTE; >> } > >
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