Probleam reading fdinfo symlinks after 30a08bf2d31d275c6fc71dd1811342777e95c831

Probleam reading fdinfo symlinks after 30a08bf2d31d275c6fc71dd1811342777e95c831

[Cyrill Gorcunov]

Hi Linus,

just tried 3.5-rc1 out and found that with commit
30a08bf2d31d275c6fc71dd1811342777e95c831 the reading
of fdinfo files returns "Too many levels of symbolic links"
error.

 | [root@neptune~]# cat /proc/`pidof crond`/fdinfo/0
 | cat: /proc/1417/fdinfo/0: Too many levels of symbolic links

so I reverted it manually and now it works as expected

 | [root@neptune ~]# cat /proc/`pidof crond`/fdinfo/0
 | pos:	0
 | flags:	0100002

I suspect this is unintentional behaviour of the commit.

Re: Probleam reading fdinfo symlinks after 30a08bf2d31d275c6fc71dd1811342777e95c831

[Linus Torvalds]

[-- Attachment #1: Type: text/plain, Size: 449 bytes --]

On Mon, Jun 4, 2012 at 8:14 AM, Cyrill Gorcunov <gorcunov@openvz.org> wrote:
>
> just tried 3.5-rc1 out and found that with commit
> 30a08bf2d31d275c6fc71dd1811342777e95c831 the reading
> of fdinfo files returns "Too many levels of symbolic links"
> error.

Ugh. The fdinfo files aren't symlinks at all, and share the revalidate function.

My bad. The fix isn't pretty, but still better than reverting things.
This should fix it.

            Linus

[-- Attachment #2: patch.diff --]
[-- Type: application/octet-stream, Size: 1423 bytes --]

 fs/proc/base.c | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 616f41a7cde6..437195f204e1 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -1803,7 +1803,7 @@ static int tid_fd_revalidate(struct dentry *dentry, struct nameidata *nd)
 			rcu_read_lock();
 			file = fcheck_files(files, fd);
 			if (file) {
-				unsigned i_mode, f_mode = file->f_mode;
+				unsigned f_mode = file->f_mode;
 
 				rcu_read_unlock();
 				put_files_struct(files);
@@ -1819,12 +1819,14 @@ static int tid_fd_revalidate(struct dentry *dentry, struct nameidata *nd)
 					inode->i_gid = GLOBAL_ROOT_GID;
 				}
 
-				i_mode = S_IFLNK;
-				if (f_mode & FMODE_READ)
-					i_mode |= S_IRUSR | S_IXUSR;
-				if (f_mode & FMODE_WRITE)
-					i_mode |= S_IWUSR | S_IXUSR;
-				inode->i_mode = i_mode;
+				if (S_ISLNK(inode->i_mode)) {
+					unsigned i_mode = S_IFLNK;
+					if (f_mode & FMODE_READ)
+						i_mode |= S_IRUSR | S_IXUSR;
+					if (f_mode & FMODE_WRITE)
+						i_mode |= S_IWUSR | S_IXUSR;
+					inode->i_mode = i_mode;
+				}
 
 				security_task_to_inode(task, inode);
 				put_task_struct(task);
@@ -1859,6 +1861,7 @@ static struct dentry *proc_fd_instantiate(struct inode *dir,
 	ei = PROC_I(inode);
 	ei->fd = fd;
 
+	inode->i_mode = S_IFLNK;
 	inode->i_op = &proc_pid_link_inode_operations;
 	inode->i_size = 64;
 	ei->op.proc_get_link = proc_fd_link;

Re: Probleam reading fdinfo symlinks after 30a08bf2d31d275c6fc71dd1811342777e95c831

[Cyrill Gorcunov]

On Mon, Jun 04, 2012 at 10:59:24AM -0700, Linus Torvalds wrote:
> On Mon, Jun 4, 2012 at 8:14 AM, Cyrill Gorcunov <gorcunov@openvz.org> wrote:
> >
> > just tried 3.5-rc1 out and found that with commit
> > 30a08bf2d31d275c6fc71dd1811342777e95c831 the reading
> > of fdinfo files returns "Too many levels of symbolic links"
> > error.
> 
> Ugh. The fdinfo files aren't symlinks at all, and share the revalidate function.
> 
> My bad. The fix isn't pretty, but still better than reverting things.
> This should fix it.

Thanks Linus! This patch fixed it.

Tested-by: Cyrill Gorcunov <gorcunov@openvz.org>