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authorGreg Kurz <groug@kaod.org>2020-09-23 22:11:45 +0800
committerDominique Martinet <asmadeus@codewreck.org>2020-11-03 09:29:56 +0100
commit478ba09edc1f2f2ee27180a06150cb2d1a686f9c (patch)
tree84615f1570076f3c5b74790496c62761db7c6662
parent987a64850996db22bbcf2c1d0a051446a343fa2c (diff)
fs/9p: search open fids first
A previous patch fixed the "create-unlink-getattr" idiom: if getattr is called on an unlinked file, we try to find an open fid attached to the corresponding inode. We have a similar issue with file permissions and setattr: open("./test.txt", O_RDWR|O_CREAT, 0666) = 4 chmod("./test.txt", 0) = 0 truncate("./test.txt", 0) = -1 EACCES (Permission denied) ftruncate(4, 0) = -1 EACCES (Permission denied) The failure is expected with truncate() but not with ftruncate(). This happens because the lookup code does find a matching fid in the dentry list. Unfortunately, this is not an open fid and the server will be forced to rely on the path name, rather than on an open file descriptor. This is the case in QEMU: the setattr operation will use truncate() and fail because of bad write permissions. This patch changes the logic in the lookup code, so that we consider open fids first. It gives a chance to the server to match this open fid to an open file descriptor and use ftruncate() instead of truncate(). This does not change the current behaviour for truncate() and other path name based syscalls, since file permissions are checked earlier in the VFS layer. With this patch, we get: open("./test.txt", O_RDWR|O_CREAT, 0666) = 4 chmod("./test.txt", 0) = 0 truncate("./test.txt", 0) = -1 EACCES (Permission denied) ftruncate(4, 0) = 0 Link: http://lkml.kernel.org/r/20200923141146.90046-4-jianyong.wu@arm.com Signed-off-by: Greg Kurz <groug@kaod.org> Signed-off-by: Jianyong Wu <jianyong.wu@arm.com> Signed-off-by: Dominique Martinet <asmadeus@codewreck.org>
-rw-r--r--fs/9p/fid.c9
1 files changed, 5 insertions, 4 deletions
diff --git a/fs/9p/fid.c b/fs/9p/fid.c
index d11dd430590d..0b23b0fe6c51 100644
--- a/fs/9p/fid.c
+++ b/fs/9p/fid.c
@@ -95,8 +95,12 @@ static struct p9_fid *v9fs_fid_find(struct dentry *dentry, kuid_t uid, int any)
dentry, dentry, from_kuid(&init_user_ns, uid),
any);
ret = NULL;
+
+ if (d_inode(dentry))
+ ret = v9fs_fid_find_inode(d_inode(dentry), uid);
+
/* we'll recheck under lock if there's anything to look in */
- if (dentry->d_fsdata) {
+ if (!ret && dentry->d_fsdata) {
struct hlist_head *h = (struct hlist_head *)&dentry->d_fsdata;
spin_lock(&dentry->d_lock);
hlist_for_each_entry(fid, h, dlist) {
@@ -106,9 +110,6 @@ static struct p9_fid *v9fs_fid_find(struct dentry *dentry, kuid_t uid, int any)
}
}
spin_unlock(&dentry->d_lock);
- } else {
- if (dentry->d_inode)
- ret = v9fs_fid_find_inode(dentry->d_inode, uid);
}
return ret;