A simple test-case from Kirill Shutemov
cat /proc/self/maps >/dev/null
chmod +x /proc/self/net/packet
exec /proc/self/net/packet
makes lockdep unhappy, cat/exec take seq_file->lock + cred_guard_mutex in
the opposite order.
It's a false positive and probably we should not allow "chmod +x" on proc
files. Still I think that we should avoid mm_access() and cred_guard_mutex
in sys_read() paths, security checking should happen at open time. Besides,
this doesn't even look right if the task changes its ->mm between m_stop()
and m_start().
Add the new "mm_struct *mm" member into struct proc_maps_private and change
proc_maps_open() to initialize it using proc_mem_open(). Change m_start() to
use priv->mm if atomic_inc_not_zero(mm_users) succeeds or return NULL (eof)
otherwise.
The only complication is that proc_maps_open() users should additionally do
mmdrop() in fop->release(), add the new proc_map_release() helper for that.
Note: this is the user-visible change, if the task execs after open("maps")
the new ->mm won't be visible via this file. I hope this is fine, and this
matches /proc/pid/mem bahaviour.
Reported-by: "Kirill A. Shutemov" <kirill@xxxxxxxxxxxxx>
Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
---
fs/proc/internal.h | 1 +
fs/proc/task_mmu.c | 37 ++++++++++++++++++++++++++++---------
2 files changed, 29 insertions(+), 9 deletions(-)
diff --git a/fs/proc/internal.h b/fs/proc/internal.h
index ba0c1c1..78784cd 100644
--- a/fs/proc/internal.h
+++ b/fs/proc/internal.h
@@ -267,6 +267,7 @@ extern int proc_remount(struct super_block *, int *, char *);
struct proc_maps_private {
struct pid *pid;
struct task_struct *task;
+ struct mm_struct *mm;
#ifdef CONFIG_MMU
struct vm_area_struct *tail_vma;
#endif
diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 794aeb6..7ec8eb5 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -165,9 +165,9 @@ static void *m_start(struct seq_file *m, loff_t *pos)
if (!priv->task)
return ERR_PTR(-ESRCH);
- mm = mm_access(priv->task, PTRACE_MODE_READ);
- if (!mm || IS_ERR(mm))
- return mm;
+ mm = priv->mm;
+ if (!mm || !atomic_inc_not_zero(&mm->mm_users))
+ return NULL;
down_read(&mm->mmap_sem);
tail_vma = get_gate_vma(mm);
@@ -240,9 +240,28 @@ static int proc_maps_open(struct inode *inode, struct file *file,
return -ENOMEM;
priv->pid = proc_pid(inode);
+ priv->mm = proc_mem_open(inode, PTRACE_MODE_READ);
+ if (IS_ERR(priv->mm)) {
+ int err = PTR_ERR(priv->mm);
+ seq_release_private(inode, file);
+ return err;
+ }
+
return 0;
}
+static int proc_map_release(struct inode *inode, struct file *file)
+{
+ struct seq_file *seq = file->private_data;
+ struct proc_maps_private *priv = seq->private;
+
+ if (priv->mm)
+ mmdrop(priv->mm);
+
+ return seq_release_private(inode, file);
+}
+
+
static int do_maps_open(struct inode *inode, struct file *file,
const struct seq_operations *ops)
{
@@ -398,14 +417,14 @@ const struct file_operations proc_pid_maps_operations = {
.open = pid_maps_open,
.read = seq_read,
.llseek = seq_lseek,
- .release = seq_release_private,
+ .release = proc_map_release,
};
const struct file_operations proc_tid_maps_operations = {
.open = tid_maps_open,
.read = seq_read,
.llseek = seq_lseek,
- .release = seq_release_private,
+ .release = proc_map_release,
};
/*
@@ -680,14 +699,14 @@ const struct file_operations proc_pid_smaps_operations = {
.open = pid_smaps_open,
.read = seq_read,
.llseek = seq_lseek,
- .release = seq_release_private,
+ .release = proc_map_release,
};
const struct file_operations proc_tid_smaps_operations = {
.open = tid_smaps_open,
.read = seq_read,
.llseek = seq_lseek,
- .release = seq_release_private,
+ .release = proc_map_release,
};
/*
@@ -1520,13 +1539,13 @@ const struct file_operations proc_pid_numa_maps_operations = {
.open = pid_numa_maps_open,
.read = seq_read,
.llseek = seq_lseek,
- .release = seq_release_private,
+ .release = proc_map_release,
};
const struct file_operations proc_tid_numa_maps_operations = {
.open = tid_numa_maps_open,
.read = seq_read,
.llseek = seq_lseek,
- .release = seq_release_private,
+ .release = proc_map_release,
};
#endif /* CONFIG_NUMA */
--
1.5.5.1
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