81 lines
2.9 KiB
Diff
81 lines
2.9 KiB
Diff
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From 562eac4226c2cf8718b8d87fc947545ccbb6dd20 Mon Sep 17 00:00:00 2001
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From: Linus Torvalds <torvalds@linux-foundation.org>
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Date: Mon, 4 Jun 2012 11:00:45 -0700
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Subject: [PATCH] vfs: Fix /proc/<tid>/fdinfo/<fd> file handling
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Cyrill Gorcunov reports that I broke the fdinfo files with commit
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30a08bf2d31d ("proc: move fd symlink i_mode calculations into
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tid_fd_revalidate()"), and he's quite right.
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The tid_fd_revalidate() function is not just used for the <tid>/fd
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symlinks, it's also used for the <tid>/fdinfo/<fd> files, and the
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permission model for those are different.
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So do the dynamic symlink permission handling just for symlinks, making
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the fdinfo files once more appear as the proper regular files they are.
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Of course, Al Viro argued (probably correctly) that we shouldn't do the
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symlink permission games at all, and make the symlinks always just be
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the normal 'lrwxrwxrwx'. That would have avoided this issue too, but
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since somebody noticed that the permissions had changed (which was the
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reason for that original commit 30a08bf2d31d in the first place), people
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do apparently use this feature.
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[ Basically, you can use the symlink permission data as a cheap "fdinfo"
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replacement, since you see whether the file is open for reading and/or
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writing by just looking at st_mode of the symlink. So the feature
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does make sense, even if the pain it has caused means we probably
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shouldn't have done it to begin with. ]
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Reported-and-tested-by: Cyrill Gorcunov <gorcunov@openvz.org>
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Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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---
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fs/proc/base.c | 17 ++++++++++-------
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1 file changed, 10 insertions(+), 7 deletions(-)
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diff --git a/fs/proc/base.c b/fs/proc/base.c
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index 2f198dad..c8cb15dc 100644
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--- a/fs/proc/base.c
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+++ b/fs/proc/base.c
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@@ -1838,7 +1838,7 @@ static int tid_fd_revalidate(struct dentry *dentry, struct nameidata *nd)
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rcu_read_lock();
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file = fcheck_files(files, fd);
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if (file) {
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- unsigned i_mode, f_mode = file->f_mode;
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+ unsigned f_mode = file->f_mode;
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rcu_read_unlock();
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put_files_struct(files);
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@@ -1854,12 +1854,14 @@ static int tid_fd_revalidate(struct dentry *dentry, struct nameidata *nd)
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inode->i_gid = 0;
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}
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- i_mode = S_IFLNK;
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- if (f_mode & FMODE_READ)
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- i_mode |= S_IRUSR | S_IXUSR;
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- if (f_mode & FMODE_WRITE)
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- i_mode |= S_IWUSR | S_IXUSR;
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- inode->i_mode = i_mode;
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+ if (S_ISLNK(inode->i_mode)) {
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+ unsigned i_mode = S_IFLNK;
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+ if (f_mode & FMODE_READ)
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+ i_mode |= S_IRUSR | S_IXUSR;
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+ if (f_mode & FMODE_WRITE)
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+ i_mode |= S_IWUSR | S_IXUSR;
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+ inode->i_mode = i_mode;
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+ }
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security_task_to_inode(task, inode);
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put_task_struct(task);
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@@ -1894,6 +1896,7 @@ static struct dentry *proc_fd_instantiate(struct inode *dir,
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ei = PROC_I(inode);
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ei->fd = fd;
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+ inode->i_mode = S_IFLNK;
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inode->i_op = &proc_pid_link_inode_operations;
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inode->i_size = 64;
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ei->op.proc_get_link = proc_fd_link;
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--
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2.17.1
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