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vfs: split out access_override_creds() 

Split out a helper that overrides the credentials in preparation for
actually doing the access check.

This prepares for the next patch that optionally disables the creds
override.

Suggested-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
This commit is contained in:
Miklos Szeredi 2020-05-14 16:44:24 +02:00
parent 9f6c61f96f
commit 9470451505
1 changed files with 24 additions and 10 deletions
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34
fs/open.c
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@ -345,21 +345,14 @@ SYSCALL_DEFINE4(fallocate, int, fd, int, mode, loff_t, offset, loff_t, len)
* We do this by temporarily clearing all FS-related capabilities and
* switching the fsuid/fsgid around to the real ones.
*/
long do_faccessat(int dfd, const char __user *filename, int mode)
static const struct cred *access_override_creds(void)
{
const struct cred *old_cred;
struct cred *override_cred;
struct path path;
struct inode *inode;
int res;
unsigned int lookup_flags = LOOKUP_FOLLOW;
if (mode & ~S_IRWXO) /* where's F_OK, X_OK, W_OK, R_OK? */
return -EINVAL;
override_cred = prepare_creds();
if (!override_cred)
return -ENOMEM;
return NULL;
override_cred->fsuid = override_cred->uid;
override_cred->fsgid = override_cred->gid;
@ -394,6 +387,28 @@ long do_faccessat(int dfd, const char __user *filename, int mode)
override_cred->non_rcu = 1;
old_cred = override_creds(override_cred);
/* override_cred() gets its own ref */
put_cred(override_cred);
return old_cred;
}
long do_faccessat(int dfd, const char __user *filename, int mode)
{
struct path path;
struct inode *inode;
int res;
unsigned int lookup_flags = LOOKUP_FOLLOW;
const struct cred *old_cred;
if (mode & ~S_IRWXO) /* where's F_OK, X_OK, W_OK, R_OK? */
return -EINVAL;
old_cred = access_override_creds();
if (!old_cred)
return -ENOMEM;
retry:
res = user_path_at(dfd, filename, lookup_flags, &path);
if (res)
@ -436,7 +451,6 @@ out_path_release:
}
out:
revert_creds(old_cred);
put_cred(override_cred);
return res;
}