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selinux: simplify and clean up inode_has_perm() 

This is a rather hot function that is called with a potentially NULL
"struct common_audit_data" pointer argument.  And in that case it has to
provide and initialize its own dummy common_audit_data structure.

However, all the _common_ cases already pass it a real audit-data
structure, so that uncommon NULL case not only creates a silly run-time
test, more importantly it causes that function to have a big stack frame
for the dummy variable that isn't even used in the common case!

So get rid of that stupid run-time behavior, and make the (few)
functions that currently call with a NULL pointer just call a new helper
function instead (naturally called inode_has_perm_noapd(), since it has
no adp argument).

This makes the run-time test be a static code generation issue instead,
and allows for a much denser stack since none of the common callers need
the dummy structure.  And a denser stack not only means less stack space
usage, it means better cache behavior.  So we have a win-win-win from
this simplification: less code executed, smaller stack footprint, and
better cache behavior.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Linus Torvalds 2011-06-08 15:11:56 -07:00
parent 4c1f683a4a
commit 95f4efb2d7
1 changed files with 15 additions and 10 deletions
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25
security/selinux/hooks.c
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@ -1476,7 +1476,6 @@ static int inode_has_perm(const struct cred *cred,
unsigned flags)
{
struct inode_security_struct *isec;
struct common_audit_data ad;
u32 sid;
validate_creds(cred);
@ -1487,15 +1486,21 @@ static int inode_has_perm(const struct cred *cred,
sid = cred_sid(cred);
isec = inode->i_security;
if (!adp) {
adp = &ad;
COMMON_AUDIT_DATA_INIT(&ad, INODE);
ad.u.inode = inode;
}
return avc_has_perm_flags(sid, isec->sid, isec->sclass, perms, adp, flags);
}
static int inode_has_perm_noadp(const struct cred *cred,
struct inode *inode,
u32 perms,
unsigned flags)
{
struct common_audit_data ad;
COMMON_AUDIT_DATA_INIT(&ad, INODE);
ad.u.inode = inode;
return inode_has_perm(cred, inode, perms, &ad, flags);
}
/* Same as inode_has_perm, but pass explicit audit data containing
the dentry to help the auditing code to more easily generate the
pathname if needed. */
@ -2122,8 +2127,8 @@ static inline void flush_unauthorized_files(const struct cred *cred,
struct tty_file_private, list);
file = file_priv->file;
inode = file->f_path.dentry->d_inode;
if (inode_has_perm(cred, inode,
FILE__READ | FILE__WRITE, NULL, 0)) {
if (inode_has_perm_noadp(cred, inode,
FILE__READ | FILE__WRITE, 0)) {
drop_tty = 1;
}
}
@ -3228,7 +3233,7 @@ static int selinux_dentry_open(struct file *file, const struct cred *cred)
* new inode label or new policy.
* This check is not redundant - do not remove.
*/
return inode_has_perm(cred, inode, open_file_to_av(file), NULL, 0);
return inode_has_perm_noadp(cred, inode, open_file_to_av(file), 0);
}
/* task security operations */