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authorAl Viro <viro@zeniv.linux.org.uk>2020-03-12 14:07:27 -0400
committerAl Viro <viro@zeniv.linux.org.uk>2020-04-02 01:09:31 -0400
commit99a4a90c8e9337e364136393286544e3753673c3 (patch)
treefa8da0e7badc7334154f0d5b400bf604cf1dac25
parentd489cf9a3e88aafc6c9f55c36ff7bbca2c25d54a (diff)
lookup_open(): don't bother with fallbacks to lookup+create
We fall back to lookup+create (instead of atomic_open) in several cases: 1) we don't have write access to filesystem and O_TRUNC is present in the flags. It's not something we want ->atomic_open() to see - it just might go ahead and truncate the file. However, we can pass it the flags sans O_TRUNC - eventually do_open() will call handle_truncate() anyway. 2) we have O_CREAT | O_EXCL and we can't write to parent. That's going to be an error, of course, but we want to know _which_ error should that be - might be EEXIST (if file exists), might be EACCES or EROFS. Simply stripping O_CREAT (and checking if we see ENOENT) would suffice, if not for O_EXCL. However, we used to have ->atomic_open() fully responsible for rejecting O_CREAT | O_EXCL on existing file and just stripping O_CREAT would've disarmed those checks. With nothing downstream to catch the problem - FMODE_OPENED used to be "don't bother with EEXIST checks, ->atomic_open() has done those". Now EEXIST checks downstream are skipped only if FMODE_CREATED is set - FMODE_OPENED alone is not enough. That has eliminated the need to fall back onto lookup+create path in this case. 3) O_WRONLY or O_RDWR when we have no write access to filesystem, with nothing else objectionable. Fallback is (and had always been) pointless. IOW, we don't really need that fallback; all we need in such cases is to trim O_TRUNC and O_CREAT properly. Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
-rw-r--r--fs/namei.c34
1 files changed, 9 insertions, 25 deletions
diff --git a/fs/namei.c b/fs/namei.c
index 1607560f2932..61fdb77a7d58 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2939,9 +2939,6 @@ static struct dentry *atomic_open(struct nameidata *nd, struct dentry *dentry,
struct inode *dir = nd->path.dentry->d_inode;
int error;
- if (!(~open_flag & (O_EXCL | O_CREAT))) /* both O_EXCL and O_CREAT */
- open_flag &= ~O_TRUNC;
-
if (nd->flags & LOOKUP_DIRECTORY)
open_flag |= O_DIRECTORY;
@@ -3038,32 +3035,20 @@ static struct dentry *lookup_open(struct nameidata *nd, struct file *file,
* Another problem is returing the "right" error value (e.g. for an
* O_EXCL open we want to return EEXIST not EROFS).
*/
+ if (unlikely(!got_write))
+ open_flag &= ~O_TRUNC;
if (open_flag & O_CREAT) {
+ if (open_flag & O_EXCL)
+ open_flag &= ~O_TRUNC;
if (!IS_POSIXACL(dir->d_inode))
mode &= ~current_umask();
- if (unlikely(!got_write)) {
- create_error = -EROFS;
- open_flag &= ~O_CREAT;
- if (open_flag & (O_EXCL | O_TRUNC))
- goto no_open;
- /* No side effects, safe to clear O_CREAT */
- } else {
+ if (likely(got_write))
create_error = may_o_create(&nd->path, dentry, mode);
- if (create_error) {
- open_flag &= ~O_CREAT;
- if (open_flag & O_EXCL)
- goto no_open;
- }
- }
- } else if ((open_flag & (O_TRUNC|O_WRONLY|O_RDWR)) &&
- unlikely(!got_write)) {
- /*
- * No O_CREATE -> atomicity not a requirement -> fall
- * back to lookup + open
- */
- goto no_open;
+ else
+ create_error = -EROFS;
}
-
+ if (create_error)
+ open_flag &= ~O_CREAT;
if (dir_inode->i_op->atomic_open) {
dentry = atomic_open(nd, dentry, file, open_flag, mode);
if (unlikely(create_error) && dentry == ERR_PTR(-ENOENT))
@@ -3071,7 +3056,6 @@ static struct dentry *lookup_open(struct nameidata *nd, struct file *file,
return dentry;
}
-no_open:
if (d_in_lookup(dentry)) {
struct dentry *res = dir_inode->i_op->lookup(dir_inode, dentry,
nd->flags);