From: "Tyler Hicks (Microsoft)" <code@xxxxxxxxxxx>
The following commits loosened the permissions of /proc/<PID>/fdinfo/
directory, as well as the files within it, from 0500 to 0555 while also
introducing a PTRACE_MODE_READ check between the current task and
<PID>'s task:
- commit 7bc3fa0172a4 ("procfs: allow reading fdinfo with PTRACE_MODE_READ")
- commit 1927e498aee1 ("procfs: prevent unprivileged processes accessing fdinfo dir")
Before those changes, inode based system calls like inotify_add_watch(2)
would fail when the current task didn't have sufficient read permissions:
[...]
lstat("/proc/1/task/1/fdinfo", {st_mode=S_IFDIR|0500, st_size=0, ...}) = 0
inotify_add_watch(64, "/proc/1/task/1/fdinfo",
IN_MODIFY|IN_ATTRIB|IN_MOVED_FROM|IN_MOVED_TO|IN_CREATE|IN_DELETE|
IN_ONLYDIR|IN_DONT_FOLLOW|IN_EXCL_UNLINK) = -1 EACCES (Permission denied)
[...]
This matches the documented behavior in the inotify_add_watch(2) man
page:
ERRORS
EACCES Read access to the given file is not permitted.
After those changes, inotify_add_watch(2) started succeeding despite the
current task not having PTRACE_MODE_READ privileges on the target task:
[...]
lstat("/proc/1/task/1/fdinfo", {st_mode=S_IFDIR|0555, st_size=0, ...}) = 0
inotify_add_watch(64, "/proc/1/task/1/fdinfo",
IN_MODIFY|IN_ATTRIB|IN_MOVED_FROM|IN_MOVED_TO|IN_CREATE|IN_DELETE|
IN_ONLYDIR|IN_DONT_FOLLOW|IN_EXCL_UNLINK) = 1757
openat(AT_FDCWD, "/proc/1/task/1/fdinfo",
O_RDONLY|O_NONBLOCK|O_CLOEXEC|O_DIRECTORY) = -1 EACCES (Permission denied)
[...]
This change in behavior broke .NET prior to v7. See the github link
below for the v7 commit that inadvertently/quietly (?) fixed .NET after
the kernel changes mentioned above.
Return to the old behavior by moving the PTRACE_MODE_READ check out of
the file .open operation and into the inode .permission operation:
[...]
lstat("/proc/1/task/1/fdinfo", {st_mode=S_IFDIR|0555, st_size=0, ...}) = 0
inotify_add_watch(64, "/proc/1/task/1/fdinfo",
IN_MODIFY|IN_ATTRIB|IN_MOVED_FROM|IN_MOVED_TO|IN_CREATE|IN_DELETE|
IN_ONLYDIR|IN_DONT_FOLLOW|IN_EXCL_UNLINK) = -1 EACCES (Permission denied)
[...]
Reported-by: Kevin Parsons (Microsoft) <parsonskev@xxxxxxxxx>
Link: https://github.com/dotnet/runtime/commit/89e5469ac591b82d38510fe7de98346cce74ad4f
Link: https://stackoverflow.com/questions/75379065/start-self-contained-net6-build-exe-as-service-on-raspbian-system-unauthorizeda
Fixes: 7bc3fa0172a4 ("procfs: allow reading fdinfo with PTRACE_MODE_READ")
Cc: stable@xxxxxxxxxxxxxxx
Cc: Christian Brauner <brauner@xxxxxxxxxx>
Cc: "Christian König" <christian.koenig@xxxxxxx>
Cc: Jann Horn <jannh@xxxxxxxxxx>
Cc: Kalesh Singh <kaleshsingh@xxxxxxxxxx>
Cc: Hardik Garg <hargar@xxxxxxxxxxxxxxxxxxx>
Cc: Allen Pais <apais@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Tyler Hicks (Microsoft) <code@xxxxxxxxxxx>
---
fs/proc/fd.c | 42 ++++++++++++++++++++----------------------
1 file changed, 20 insertions(+), 22 deletions(-)
diff --git a/fs/proc/fd.c b/fs/proc/fd.c
index 6e72e5ad42bc..f4b1c8b42a51 100644
--- a/fs/proc/fd.c
+++ b/fs/proc/fd.c
@@ -74,7 +74,18 @@ static int seq_show(struct seq_file *m, void *v)
return 0;
}
-static int proc_fdinfo_access_allowed(struct inode *inode)
+static int seq_fdinfo_open(struct inode *inode, struct file *file)
+{
+ return single_open(file, seq_show, inode);
+}
+
+/**
+ * Shared /proc/pid/fdinfo and /proc/pid/fdinfo/fd permission helper to ensure
+ * that the current task has PTRACE_MODE_READ in addition to the normal
+ * POSIX-like checks.
+ */
+static int proc_fdinfo_permission(struct mnt_idmap *idmap, struct inode *inode,
+ int mask)
{
bool allowed = false;
struct task_struct *task = get_proc_task(inode);
@@ -88,18 +99,13 @@ static int proc_fdinfo_access_allowed(struct inode *inode)
if (!allowed)
return -EACCES;
- return 0;
+ return generic_permission(idmap, inode, mask);
}
-static int seq_fdinfo_open(struct inode *inode, struct file *file)
-{
- int ret = proc_fdinfo_access_allowed(inode);
-
- if (ret)
- return ret;
-
- return single_open(file, seq_show, inode);
-}
+static const struct inode_operations proc_fdinfo_file_inode_operations = {
+ .permission = proc_fdinfo_permission,
+ .setattr = proc_setattr,
+};
static const struct file_operations proc_fdinfo_file_operations = {
.open = seq_fdinfo_open,
@@ -388,6 +394,8 @@ static struct dentry *proc_fdinfo_instantiate(struct dentry *dentry,
ei = PROC_I(inode);
ei->fd = data->fd;
+ inode->i_op = &proc_fdinfo_file_inode_operations;
+
inode->i_fop = &proc_fdinfo_file_operations;
tid_fd_update_inode(task, inode, 0);
@@ -407,23 +415,13 @@ static int proc_readfdinfo(struct file *file, struct dir_context *ctx)
proc_fdinfo_instantiate);
}
-static int proc_open_fdinfo(struct inode *inode, struct file *file)
-{
- int ret = proc_fdinfo_access_allowed(inode);
-
- if (ret)
- return ret;
-
- return 0;
-}
-
const struct inode_operations proc_fdinfo_inode_operations = {
.lookup = proc_lookupfdinfo,
+ .permission = proc_fdinfo_permission,
.setattr = proc_setattr,
};
const struct file_operations proc_fdinfo_operations = {
- .open = proc_open_fdinfo,
.read = generic_read_dir,
.iterate_shared = proc_readfdinfo,
.llseek = generic_file_llseek,
--
2.34.1
