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Subject[PATCH -V14 10/11] vfs: Support null pathname in faccessat
Date
This enables to use faccessat to get the access check details
from a file descriptor pointing to the file. This can be used
with open_by_handle syscall that returns a file descriptor.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
---
fs/open.c | 27 ++++++++++++++++++++-------
1 files changed, 20 insertions(+), 7 deletions(-)
diff --git a/fs/open.c b/fs/open.c
index 43093af..90fb12f 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -288,7 +288,8 @@ SYSCALL_DEFINE3(faccessat, int, dfd, const char __user *, filename, int, mode)
{
const struct cred *old_cred;
struct cred *override_cred;
- struct path path;
+ struct file *file = NULL;
+ struct path path, *pp;
struct inode *inode;
int res;

@@ -312,12 +313,21 @@ SYSCALL_DEFINE3(faccessat, int, dfd, const char __user *, filename, int, mode)
}

old_cred = override_creds(override_cred);
-
- res = user_path_at(dfd, filename, LOOKUP_FOLLOW, &path);
+ if (filename == NULL && dfd != AT_FDCWD) {
+ file = fget(dfd);
+ if (file) {
+ pp = &file->f_path;
+ res = 0;
+ } else
+ res = -EBADF;
+ } else {
+ res = user_path_at(dfd, filename, LOOKUP_FOLLOW, &path);
+ pp = &path;
+ }
if (res)
goto out;

- inode = path.dentry->d_inode;
+ inode = pp->dentry->d_inode;

if ((mode & MAY_EXEC) && S_ISREG(inode->i_mode)) {
/*
@@ -325,7 +335,7 @@ SYSCALL_DEFINE3(faccessat, int, dfd, const char __user *, filename, int, mode)
* with the "noexec" flag.
*/
res = -EACCES;
- if (path.mnt->mnt_flags & MNT_NOEXEC)
+ if (pp->mnt->mnt_flags & MNT_NOEXEC)
goto out_path_release;
}

@@ -343,11 +353,14 @@ SYSCALL_DEFINE3(faccessat, int, dfd, const char __user *, filename, int, mode)
* inherently racy and know that the fs may change
* state before we even see this result.
*/
- if (__mnt_is_readonly(path.mnt))
+ if (__mnt_is_readonly(pp->mnt))
res = -EROFS;

out_path_release:
- path_put(&path);
+ if (file)
+ fput(file);
+ else
+ path_put(&path);
out:
revert_creds(old_cred);
put_cred(override_cred);
--
1.7.1.331.ga5080


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