This ensures that VFS implementations don't call ptrace_may_access() from
VFS read or write handlers. In order for file descriptor passing to have
its intended security properties, VFS read/write handlers must not do any
kind of privilege checking.
Signed-off-by: Jann Horn <jann@xxxxxxxxx>
---
fs/aio.c | 2 ++
fs/read_write.c | 12 ++++++++++++
fs/splice.c | 12 ++++++++++--
include/linux/sched.h | 4 ++++
kernel/ptrace.c | 7 +++++++
5 files changed, 35 insertions(+), 2 deletions(-)
diff --git a/fs/aio.c b/fs/aio.c
index fb8e45b..c941885 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -1454,9 +1454,11 @@ rw_common:
if (rw == WRITE)
file_start_write(file);
+ current->in_unprivileged_vfs++;
ret = iter_op(req, &iter);
+ current->in_unprivileged_vfs--;
if (rw == WRITE)
file_end_write(file);
kfree(iovec);
diff --git a/fs/read_write.c b/fs/read_write.c
index 66215a7..deddb93 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -472,7 +472,9 @@ ssize_t vfs_read(struct file *file, char __user *buf, size_t count, loff_t *pos)
if (!ret) {
if (count > MAX_RW_COUNT)
count = MAX_RW_COUNT;
+ current->in_unprivileged_vfs++;
ret = __vfs_read(file, buf, count, pos);
+ current->in_unprivileged_vfs--;
if (ret > 0) {
fsnotify_access(file);
add_rchar(current, ret);
@@ -557,7 +559,9 @@ ssize_t vfs_write(struct file *file, const char __user *buf, size_t count, loff_
if (count > MAX_RW_COUNT)
count = MAX_RW_COUNT;
file_start_write(file);
+ current->in_unprivileged_vfs++;
ret = __vfs_write(file, buf, count, pos);
+ current->in_unprivileged_vfs--;
if (ret > 0) {
fsnotify_modify(file);
add_wchar(current, ret);
@@ -838,12 +842,14 @@ static ssize_t do_readv_writev(int type, struct file *file,
iter_fn = file->f_op->write_iter;
file_start_write(file);
}
+ current->in_unprivileged_vfs++;
if (iter_fn)
ret = do_iter_readv_writev(file, &iter, pos, iter_fn, flags);
else
ret = do_loop_readv_writev(file, &iter, pos, fn, flags);
+ current->in_unprivileged_vfs--;
if (type != READ)
file_end_write(file);
@@ -1063,12 +1069,14 @@ static ssize_t compat_do_readv_writev(int type, struct file *file,
iter_fn = file->f_op->write_iter;
file_start_write(file);
}
+ current->in_unprivileged_vfs++;
if (iter_fn)
ret = do_iter_readv_writev(file, &iter, pos, iter_fn, flags);
else
ret = do_loop_readv_writev(file, &iter, pos, fn, flags);
+ current->in_unprivileged_vfs--;
if (type != READ)
file_end_write(file);
@@ -1369,7 +1377,9 @@ static ssize_t do_sendfile(int out_fd, int in_fd, loff_t *ppos,
fl = SPLICE_F_NONBLOCK;
#endif
file_start_write(out.file);
+ current->in_unprivileged_vfs++;
retval = do_splice_direct(in.file, &pos, out.file, &out_pos, count, fl);
+ current->in_unprivileged_vfs--;
file_end_write(out.file);
if (retval > 0) {
@@ -1512,6 +1522,7 @@ ssize_t vfs_copy_file_range(struct file *file_in, loff_t pos_in,
ret = mnt_want_write_file(file_out);
if (ret)
return ret;
+ current->in_unprivileged_vfs++;
ret = -EOPNOTSUPP;
if (file_out->f_op->copy_file_range)
@@ -1521,6 +1532,7 @@ ssize_t vfs_copy_file_range(struct file *file_in, loff_t pos_in,
ret = do_splice_direct(file_in, &pos_in, file_out, &pos_out,
len > MAX_RW_COUNT ? MAX_RW_COUNT : len, 0);
+ current->in_unprivileged_vfs--;
if (ret > 0) {
fsnotify_access(file_in);
add_rchar(current, ret);
diff --git a/fs/splice.c b/fs/splice.c
index dd9bf7e..5fcad56 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -1134,7 +1134,7 @@ static long do_splice_to(struct file *in, loff_t *ppos,
{
ssize_t (*splice_read)(struct file *, loff_t *,
struct pipe_inode_info *, size_t, unsigned int);
- int ret;
+ long ret;
if (unlikely(!(in->f_mode & FMODE_READ)))
return -EBADF;
@@ -1151,7 +1151,11 @@ static long do_splice_to(struct file *in, loff_t *ppos,
else
splice_read = default_file_splice_read;
- return splice_read(in, ppos, pipe, len, flags);
+ current->in_unprivileged_vfs++;
+ ret = splice_read(in, ppos, pipe, len, flags);
+ current->in_unprivileged_vfs--;
+
+ return ret;
}
/**
@@ -1334,7 +1338,9 @@ long do_splice_direct(struct file *in, loff_t *ppos, struct file *out,
if (unlikely(ret < 0))
return ret;
+ current->in_unprivileged_vfs++;
ret = splice_direct_to_actor(in, &sd, direct_splice_actor);
+ current->in_unprivileged_vfs--;
if (ret > 0)
*ppos = sd.pos;
@@ -1401,7 +1407,9 @@ static long do_splice(struct file *in, loff_t __user *off_in,
return ret;
file_start_write(out);
+ current->in_unprivileged_vfs++;
ret = do_splice_from(ipipe, out, &offset, len, flags);
+ current->in_unprivileged_vfs--;
file_end_write(out);
if (!off_out)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index e4bf894..6094720 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1473,6 +1473,10 @@ struct task_struct {
atomic_t usage;
unsigned int flags; /* per process flags, defined below */
unsigned int ptrace;
+ /* depth of VFS read/write; non-zero values let certain privilege checks
+ * fail with a warning
+ */
+ unsigned int in_unprivileged_vfs;
#ifdef CONFIG_SMP
struct llist_node wake_entry;
diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index b311ca5..d839919 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -302,6 +302,13 @@ ok:
bool ptrace_may_access(struct task_struct *task, unsigned int mode)
{
int err;
+
+ /* If you have to check for ptrace access from a VFS method, use
+ * ptrace_may_access_noncurrent() instead.
+ */
+ if (WARN_ON(current->in_unprivileged_vfs != 0))
+ return false;
+
task_lock(task);
err = __ptrace_may_access(task, mode, current_cred(),
¤t->self_privunit_id);
--
2.1.4
--
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