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do_last(): don't bother with keeping got_write in FMODE_OPENED case

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it's easier to drop it right after lookup_open() and regain if
needed (i.e. if we will need to truncate).  On the non-FMODE_OPENED
path we do that anyway.  In case of FMODE_CREATED we won't be
needing it.  And it's easier to prove correctness that way,
especially since the initial failure to get write access is not
always fatal; proving that we'll never end up truncating in that
case is rather convoluted.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro 2020-01-26 10:22:24 -05:00
parent 3ad5615a07
commit 59e96e6583
1 changed files with 11 additions and 20 deletions
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31
fs/namei.c
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@ -3191,11 +3191,14 @@ static const char *do_last(struct nameidata *nd,
else
inode_unlock_shared(dir->d_inode);
if (IS_ERR(dentry)) {
error = PTR_ERR(dentry);
goto out;
if (got_write) {
mnt_drop_write(nd->path.mnt);
got_write = false;
}
if (IS_ERR(dentry))
return ERR_CAST(dentry);
if (file->f_mode & FMODE_OPENED) {
if (file->f_mode & FMODE_CREATED) {
open_flag &= ~O_TRUNC;
@ -3220,16 +3223,6 @@ static const char *do_last(struct nameidata *nd,
goto finish_open_created;
}
/*
* If atomic_open() acquired write access it is dropped now due to
* possible mount and symlink following (this might be optimized away if
* necessary...)
*/
if (got_write) {
mnt_drop_write(nd->path.mnt);
got_write = false;
}
finish_lookup:
if (nd->depth)
put_link(nd);
@ -3250,27 +3243,25 @@ static const char *do_last(struct nameidata *nd,
return ERR_PTR(error);
audit_inode(nd->name, nd->path.dentry, 0);
if (open_flag & O_CREAT) {
error = -EISDIR;
if (d_is_dir(nd->path.dentry))
goto out;
return ERR_PTR(-EISDIR);
error = may_create_in_sticky(dir_mode, dir_uid,
d_backing_inode(nd->path.dentry));
if (unlikely(error))
goto out;
return ERR_PTR(error);
}
error = -ENOTDIR;
if ((nd->flags & LOOKUP_DIRECTORY) && !d_can_lookup(nd->path.dentry))
goto out;
return ERR_PTR(-ENOTDIR);
if (!d_is_reg(nd->path.dentry))
will_truncate = false;
finish_open_created:
if (will_truncate) {
error = mnt_want_write(nd->path.mnt);
if (error)
goto out;
return ERR_PTR(error);
got_write = true;
}
finish_open_created:
error = may_open(&nd->path, acc_mode, open_flag);
if (error)
goto out;